Application of GIS,remote sensing and mathematical modelling for wetland management: A case study of the Inner Niger Delta
Application of GIS,remote sensing and mathematical modelling for wetland management
A case study of the Inner Niger Delta
Introduction:
Environmental problems in the humid tropical regions, where the focus is on the fate and management of the surviving rainforest and climate change, are attracting increasing attention internationally. The distribution of tropical rainfall is highly variable, and in many regions the supply of potable water is inadequate. By the end of the century one-third of the worldâs population will be living in the humid tropics. This book considers all aspects of hydrology in the humid tropics. The first four parts of the book cover the physical basis of hydrology in the humid tropics: climatology, meteorology, process hydrology, sedimentation, water quality and freshwater ecology. This is followed by extensive treatment of the human and societal issues: land-use changes, water resource management, and rural and urban water supply in the tropical regions. The book is a uniquely integrated summary of hydrology in the tropics.
We will study follwing that map :
- Description of the study area
1.a) description of wetlands
1.b) technical definitions
1.c) Ramsar convention definition
1.d) Regional definitions
1.e) Conservation
1.f) Ramsar convention
1.g) Climate
- GIS and remote sensing on wetland
2.a) GIS desciption
2.b) Applications
2.c) History of development
2.d) GIS software
2.e) GIS Techniques and Technology
2.f) Relating information from different sources
2.g) Data representation
2.h) Raster
2.i) Vectors
2.j) Advantages and disadvantages
2.k) Non-spatial data
2.l) data capture
2.m) Raster-to-vector translation
2.n) Projections, coordinate systems and registration
- Spatial analysis with GIS
3.a) data modeling
3.b) topological modeling
3.c) Networks
3.d) automated cartography
4.Geostatistics
4.a) data geocoding
4.b) reverse geocoding
4.c) Data output and cartography
4.d) Graphic display techniques
- GIS developments
5.a) OGC standards
5.b) Global change, climate history program and prediction of its impact
5.c) Adding the dimension of time
5.d) Semantics
5.e) society
- Evapotranspiration
- a) definition
- b) Diverse expressions of the evapotranspiration
Units of measure and orders of height of the ETp
- Inner Nigger delta
- a) location and description
- b) ecology
c)Threats and preservation
- Modelisation
- Conclusion
- Further eading
- Description of the study area
- a) Description of wetlands
A wetland is an area of land whose soil is saturated with moisture either permanently or seasonally. Such areas may also be covered partially or completely by shallow pools of water. Wetlands include swamps, marshes, and bogs, among others. The water found in wetlands can be saltwater, freshwater, or brackish. The world’s largest wetland is the Pantanal which straddles Brazil, Bolivia and Paraguay in South America. Wetlands should be kept safe and from harm of ecological dangers.
Wetlands are considered the most biologically diverse of all ecosystems. Plant life found in wetlands includes mangrove, water lilies, cattails, sedges, tamarack, black spruce, cypress, gum, .and many others. Animal life includes many different amphibians, reptiles, birds, and furbearers.[3]
In many locations, such as the United Kingdom, Iraq, South Africa and the United States, wetlands are the subject of conservation efforts and Biodiversity Action Plans.
The study of wetlands has recently been termed paludology in some publications.
b)Technical definitions
Wetlands have been categorized both as biomes and ecosystems.They are generally distinguished from other water bodies or landforms based on their water level and on the types of plants that thrive within them. Specifically, wetlands are characterized as having a water table that stands at or near the land surface for a long enough season each year to support aquatic plants.Put simply, wetlands are lands made up of hydric soil.
Wetlands have also been described as ecotones, providing a transition between dry land and water bodies.Mitsch and Gosselink write that wetlands exist « …at the interface between truly terrestrial ecosystems and aquatic systems, making them inherently different from each other, yet highly dependent on both. »
c) Ramsar Convention definition
Under the Ramsar international wetland conservation treaty, wetlands are defined as follows:
- Article 1.1: « …wetlands are areas of marsh, fen, peatland or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six metres. »
- Article 2.1: « [Wetlands] may incorporate riparian and coastal zones adjacent to the wetlands, and islands or bodies of marine water deeper than six metres at low tide lying within the wetlands ».
d) Regional definitions
In the United States, wetlands are defined as « those areas that are inundated or saturated by surface or groundwater at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally include swamps, marshes, bogs and similar areas »[9]. Some states, such as Massachusetts and New York, have separate definitions that may differ from United States federal laws.
e) Conservation
Due to their lack of potential financial benefits, wetlands have historically been the victim of large-scale draining efforts for real estate development, or flooding for use as recreational lakes. Wetlands provide a valuable flood control function, but building levees helps replace natural flood controls. Wetlands were very effective at filtering and cleaning water, so to help with the ever increasing challenge of decreasing water pollution (often from agricultural runoff from the farms that replaced the wetlands in the first place), millions of dollars have been invested on water purification plants and expensive remediation measures. The USA came to understand how biologically productive wetlands are, so the USA passed laws limiting wetlands destruction, and created requirements that if a wetland had to be drained, developers at least had to offset the loss by creating artificial wetlands. One example is the project by the U.S. Army Corps of Engineers to control flooding and enhance development by taming the Everglades, a project which has now been reversed to restore much of the wetlands as a natural habitat for plant and animal life, as well as a method of flood control.
By 1993 half the world’s wetlands had been drained. Since the 1970s, more focus has been put on preserving wetlands for their natural function — sometimes also at great expense.
The South African Department of Environmental Affairs and Tourism in conjunction with the departments of Water Affairs and Forestry, and of Agriculture, supports the conservation and rehabilitation of wetlands through the Working for Wetlands program.The aim of this program is to encourage the protection, rehabilitation and sustainable use of South African wetlands through co-operative governance and partnerships. The program is also a poverty relief effort, providing employment in wetland maintenance.
Over 90% of the wetlands in New Zealand have been drained since European settlement, predominantly to create farmland. Wetlands now have a degree of protection under the Resource Management Act.
f) Ramsar Convention
The Convention on Wetlands of International Importance, especially as Waterfowl Habitat, or Ramsar Convention, is an international treaty designed to address global concerns regarding wetland loss and degradation. The primary purposes of the treaty are to list wetlands of international importance and to promote their wise use, with the ultimate goal of preserving the world’s wetlands. Methods include restricting access to the majority portion of wetland areas, as well as educating the public to combat the misconception that wetlands are wastelands.
There are many remote sensing methods that can be used to map wetlands. Remote-sensing technology permits the acquisition of timely digital data on a repetitive basis. This repeat coverage allows wetlands, as well as the adjacent land-cover and land-use types, to be monitored seasonally and/or annually. Using digital data provides a standardized data-collection procedure and an opportunity for data integration within a geographic information system. Traditionally, Landsat 5 Thematic Mapper (TM), Landsat 7 Enhanced Thematic Mapper Plus (ETM + ), and the SPOT 4 and 5 satellite systems have been used for this purpose. More recently, however, multispectral IKONOS and QuickBird data, with spatial resolutions of 4m by 4m and 2.44m by 2.44 m, respectively, have been shown to be excellent sources of data when mapping and monitoring smaller wetland habitats and vegetation communities.
A wide range of remote sensing studies has been undertaken in a variety of wetland environments. Remote sensing technology has permitted the acquisition of timely digital data on a repetitive basis. For example, the wetlands and vegetation within Detroit Lakes Wetland management District has been assessed using remote sensing. In mapping and monitoring large geographic areas, analysis of satellite images is less costly and time-consuming compared to visual interpretation of aerial photographs. Aerial photographs also require experienced interpreters to extract information based on structure and texture while remote sensing only requires the analysis of the spectral characteristics of data.
However, there are a number of limitations associated with image acquisition. Analysis of wetlands has proved difficult because to obtain the data, it has to be linked with practical purposes such as the analysis of land cover or land use. Wetlands, in particular are difficult to monitor, are often difficult to access, especially their inner reaches, and are sometimes home to dangerous wildlife and endemic diseases. Developing a global inventory of wetlands has proven to be a large and difficult undertaking. Current efforts are based on available data, but both classification and spatial resolution may be inadequate for regional or site-specific management decision-making. It is difficult to identify small, long, and narrow wetlands within the landscape. Current efforts using today’s remote sensing satellites may not have sufficient spatial and spectral resolution to monitor wetland conditions, although multispectral IKONOS and QuickBird data may offer improved spatial resolutions of 4m or higher. Majority of the pixels are just mixtures of several plant species or vegetation types and are difficult to isolate. Improved remote sensing information, coupled with good knowledge domain on wetlands will facilitate expanded efforts in wetland monitoring and mapping. This will also be extremely important because we expect to see major shifts in species composition due to both anthropogenic (land use) and natural changes in the environment caused by climate change. Methods to focus the classification on specific classes of interest so that identification can be done with very high accuracies should be looked into. The issue of the cost and expertise involved in remote sensing technology is still a factor hindering further advancements in image acquisition and data processing. Future improvements in wetland vegetation mapping could include the use of more recent and better geospatial data.
g) Climate
Temperature
Temperatures vary greatly depending on the location of the wetland. Many of the world’s wetlands are in temperate zones (midway between the North and South Poles and the equator). In these zones, summers are warm and winters are cold, but temperatures are not extreme. However, wetlands found in the tropic zone, which is around the equator, are always warm. Temperatures in wetlands on the Arabian Peninsula, for example, can reach 50 °C (122 °F). In northeastern Siberia, which has a polar climate, wetland temperatures can be as cold as −50 °C (−58 °F).
Rainfall
The amount of rainfall a wetland receives depends upon its location. Wetlands in Wales, Scotland, and Western Ireland receive about 150 cm (59 in) per year. Those in Southeast Asia, where heavy rains occur, can receive up to 500 cm (200 in). In the northern areas of North America, wetlands exist where as little as 15 cm (6 in) of rain fall each year.
List of wetland types
| · Swamp
· Freshwater swamp forest · Marsh · Salt marsh · Bog · Peat swamp forest · |
· Slough
· Flooded grasslands and savannas · Constructed wetland · Riparian zone |
- GIS and remote sensing on wetland
- a) GIS description :
A Geographic Information System (GIS), or Geographical Information System is any system that captures, stores, analyzes, manages, and presents data that is linked to location. Technically, a GIS is a system that includes mapping software and its application to remote sensing, land surveying, aerial photography, mathematics, photogrammetry, geography, and tools that can be implemented with GIS software. Still, many refer to « Geographic Information System » as « GIS » even though it doesn’t cover all tools connected to topology.
In the strictest sense, the term describes any information system that integrates, stores, edits, analyzes, shares, and displays geographic information. In a more generic sense, GIS applications are tools that allow users to create interactive queries (user-created searches), analyze spatial information, edit data, maps, and present the results of all these operations. Geographic Information Science is the science underlying the geographic concepts, applications and systems, taught in degree and GIS Certificate programs at many universities.
In the simplest terms, GIS is the merging of cartography and database technology. Consumer users would likely be familiar with applications for finding driving directions, like a GPS program on their hand-held device. GPS (Global Positioning System) is the real-time location component that uses satellites to show your current position, « where am I now » on your device. GPS technology is discussed in more detail later in this article.
- b) Applications
GIS technology can be used for scientific investigations, resource management, asset management, archaeology, environmental impact assessment, urban planning, cartography, criminology, geographic history, marketing, logistics, prospectivity mapping, and other purposes. For example, GIS might allow emergency planners to easily calculate emergency response times (i.e. logistics) in the event of a natural disaster, GIS might be used to find wetlands that need protection from pollution, or GIS can be used by a company to site a new business location to take advantage of a previously under-served market.
c) History of development
About 15,500 years ago, on the walls of caves near Lascaux, France, Cro-Magnon hunters drew pictures of the animals they hunted. Associated with the animal drawings are track lines and tallies thought to depict migration routes. While simplistic in comparison to modern technologies, these early records mimic the two-element structure of modern GIS, an image associated with attribute information.
In 1854, John Snow depicted a cholera outbreak in London using points to represent the locations of some individual cases, possibly the earliest use of the geographic method.[4] His study of the distribution of cholera led to the source of the disease, a contaminated water pump (the Broad Street Pump, whose handle he disconnected, thus terminating the outbreak) within the heart of the cholera outbreak.
- W. Gilbert’s version (1958) of John Snow’s 1855 map of the Soho cholera outbreak showing the clusters of cholera cases in the London epidemic of 1854
While the basic elements of topography and theme existed previously in cartography, the John Snow map was unique, using cartographic methods not only to depict but also to analyze clusters of geographically dependent phenomena for the first time.
The early 20th century saw the development of photolithography, by which maps were separated into layers. Computer hardware development spurred by nuclear weapon research would lead to general-purpose computer « mapping » applications by the early 1960s.
The year 1962 saw the development of the world’s first true operational GIS in Ottawa, Ontario, Canada by the federal Department of Forestry and Rural Development. Developed by Dr. Roger Tomlinson, it was called the « Canada Geographic Information System » (CGIS) and was used to store, analyze, and manipulate data collected for the Canada Land Inventory (CLI)—an initiative to determine the land capability for rural Canada by mapping information about soils, agriculture, recreation, wildlife, waterfowl, forestry, and land use at a scale of 1:50,000. A rating classification factor was also added to permit analysis.
CGIS was the world’s first « system » and was an improvement over « mapping » applications as it provided capabilities for overlay, measurement, and digitizing/scanning. It supported a national coordinate system that spanned the continent, coded lines as « arcs » having a true embedded topology, and it stored the attribute and locational information in separate files. As a result of this, Tomlinson has become known as the « father of GIS, » particularly for his use of overlays in promoting the spatial analysis of convergent geographic data. CGIS lasted into the 1990s and built the largest digital land resource database in Canada. It was developed as a mainframe based system in support of federal and provincial resource planning and management. Its strength was continent-wide analysis of complex datasets. The CGIS was never available in a commercial form.
In 1964, Howard T Fisher formed the Laboratory for Computer Graphics and Spatial Analysis at the Harvard Graduate School of Design (LCGSA 1965-1991), where a number of important theoretical concepts in spatial data handling were developed, and which by the 1970s had distributed seminal software code and systems, such as ‘SYMAP’, ‘GRID’, and ‘ODYSSEY’ — which served as literal and inspirational sources for subsequent commercial development—to universities, research centers, and corporations worldwide.
By the early 1980s, M&S Computing (later Intergraph), Environmental Systems Research Institute (ESRI) and CARIS (Computer Aided Resource Information System) emerged as commercial vendors of GIS software, successfully incorporating many of the CGIS features, combining the first generation approach to separation of spatial and attribute information with a second generation approach to organizing attribute data into database structures. In parallel, the development of two public domain systems began in the late 1970s and early 1980s.[8] MOSS, the Map Overlay and Statistical System project started in 1977 in Fort Collins, Colorado under the auspices of the Western Energy and Land Use Team (WELUT) and the US Fish and Wildlife Service. GRASS GIS was begun in 1982 by the U.S. Army Corps of Engineering Research Laboratory (USA-CERL) in Champaign, Illinois, a branch of the U.S. Army Corps of Engineers to meet the need of the United States military for software for land management and environmental planning. The later 1980s and 1990s industry growth were spurred on by the growing use of GIS on Unix workstations and the personal computer. By the end of the 20th century, the rapid growth in various systems had been consolidated and standardized on relatively few platforms and users were beginning to export the concept of viewing GIS data over the Internet, requiring data format and transfer standards. More recently, there are a growing number of free, open source GIS packages which run on a range of operating systems and can be customized to perform specific tasks.
d) GIS software
Main articles: GIS software and List of GIS software
Geographic information can be accessed, transferred, transformed, overlaid, processed and displayed using numerous software applications. Within industry, commercial offerings from companies such as Autodesk, Bentley Systems, ESRI, Intergraph, Manifold System, Mapinfo, Smallworld and ERDAS dominate, offering an entire suite of tools. Government and military departments often use custom software, open source products such as GRASS or uDig, or more specialized products that meet a well defined need. Although free tools exist to view GIS datasets, public access to geographic information is dominated by online resources such as Google Earth and interactive web mapping.
Originally up to the late 1990s, when GIS data was mostly based on large computers and used to maintain internal records, software was a stand-alone product. However with increased access to the internet and networks and demand for distributed geographic data grew, GIS software gradually changed its entire outlook to the delivery of data over a network. GIS software is now usually marketed as combination of various interoperable applications and APIs. It helps to automate many complex processes without worrying about underlying algorithms and processing steps in conventional GIS software.
e) GIS Techniques and Technology
Modern GIS technologies use digital information, for which various digitized data creation methods are used. The most common method of data creation is digitization, where a hard copy map or survey plan is transferred into a digital medium through the use of a computer-aided design (CAD) program, and geo-referencing capabilities. With the wide availability of ortho-rectified imagery (both from satellite and aerial sources), heads-up digitizing is becoming the main avenue through which geographic data is extracted. Heads-up digitizing involves the tracing of geographic data directly on top of the aerial imagery instead of by the traditional method of tracing the geographic form on a separate digitizing tablet (heads-down digitizing).
f) Relating information from different sources
Location may be annotated by x, y, and z coordinates of longitude, latitude, and elevation, or by other geocode systems like ZIP Codes or by highway mile markers. Any variable that can be located spatially can be fed into a GIS. Several computer databases that can be directly entered into a GIS are being produced by government agencies and non-government organizations[citation needed]. Different kinds of data in map form can be entered into a GIS.
A GIS (Geographic Information System) can also convert existing digital information, which may not yet be in map form, into forms it can recognize and use. For example, digital satellite images generated through remote sensing can be analyzed to produce a map-like layer of digital information about vegetative covers. Another fairly recently developed resource for naming GIS objects is the Getty Thesaurus of Geographic Names (GTGN), which is a structured vocabulary containing around 1,000,000 names and other information about places.[9]
Likewise, census or hydrological tabular data can be converted to map-like form, serving as layers of thematic information in a GIS.and map layout
g) Data representation
GIS data represents real world objects (roads, land use, elevation) with digital data. Real world objects can be divided into two abstractions: discrete objects (a house) and continuous fields (rain fall amount or elevation). Traditionally, there are two broad methods used to store data in a GIS for both abstractions: Raster and Vector. A new hybrid method of storing data is point clouds, which combine 3d points with RGB information at each point, returning a « 3d color image ».
h) Raster
A raster data type is, in essence, any type of digital image represented in grids. Anyone who is familiar with digital photography will recognize the pixel as the smallest individual unit of an image. A combination of these pixels will create an image, distinct from the commonly used scalable vector graphics which are the basis of the vector model. While a digital image is concerned with the output as representation of reality, in a photograph or art transferred to computer, the raster data type will reflect an abstraction of reality. Aerial photos are one commonly used form of raster data, with only one purpose, to display a detailed image on a map or for the purposes of digitization. Other raster data sets will contain information regarding elevation, a DEM, or reflectance of a particular wavelength of light, LANDSAT.
Digital elevation model, map (image), and vector data
Raster data type consists of rows and columns of cells, with each cell storing a single value. Raster data can be images (raster images) with each pixel (or cell) containing a color value. Additional values recorded for each cell may be a discrete value, such as land use, a continuous value, such as temperature, or a null value if no data is available. While a raster cell stores a single value, it can be extended by using raster bands to represent RGB (red, green, blue) colors, colormaps (a mapping between a thematic code and RGB value), or an extended attribute table with one row for each unique cell value. The resolution of the raster data set is its cell width in ground units.
Raster data is stored in various formats; from a standard file-based structure of TIF, JPEG, etc. to binary large object (BLOB) data stored directly in a relational database management system (RDBMS) similar to other vector-based feature classes. Database storage, when properly indexed, typically allows for quicker retrieval of the raster data but can require storage of millions of significantly-sized records.
i) Vector
In a GIS, geographical features are often expressed as vectors, by considering those features as geometrical shapes. Different geographical features are expressed by different types of geometry:
- Points
A simple vector map, using each of the vector elements: points for wells, lines for rivers, and a polygon for the lake.
Zero-dimensional points are used for geographical features that can best be expressed by a single point reference; in other words, simple location. For example, the locations of wells, peak elevations, features of interest or trailheads. Points convey the least amount of information of these file types. Points can also be used to represent areas when displayed at a small scale. For example, cities on a map of the world would be represented by points rather than polygons. No measurements are possible with point features.
- Lines or polylines
One-dimensional lines or polylines are used for linear features such as rivers, roads, railroads, trails, and topographic lines. Again, as with point features, linear features displayed at a small scale will be represented as linear features rather than as a polygon. Line features can measure distance.
- Polygons
Two-dimensional polygons are used for geographical features that cover a particular area of the earth’s surface. Such features may include lakes, park boundaries, buildings, city boundaries, or land uses. Polygons convey the most amount of information of the file types. Polygon features can measure perimeter and area.
Each of these geometries is linked to a row in a database that describes their attributes. For example, a database that describes lakes may contain a lake’s depth, water quality, pollution level. This information can be used to make a map to describe a particular attribute of the dataset. For example, lakes could be coloured depending on level of pollution. Different geometries can also be compared. For example, the GIS could be used to identify all wells (point geometry) that are within one kilometre of a lake (polygon geometry) that has a high level of pollution.
Vector features can be made to respect spatial integrity through the application of topology rules such as ‘polygons must not overlap’. Vector data can also be used to represent continuously varying phenomena. Contour lines and triangulated irregular networks (TIN) are used to represent elevation or other continuously changing values. TINs record values at point locations, which are connected by lines to form an irregular mesh of triangles. The face of the triangles represent the terrain surface.
j)Advantages and disadvantages
There are some important advantages and disadvantages to using a raster or vector data model to represent reality:
– Raster datasets record a value for all points in the area covered which may require more storage space than representing data in a vector format that can store data only where needed.
– Raster data allows easy implementation of overlay operations, which are more difficult with vector data.
– Vector data can be displayed as vector graphics used on traditional maps, whereas raster data will appear as an image that may have a blocky appearance for object boundaries. (depending on the resolution of the raster file)
– Vector data can be easier to register, scale, and re-project, which can simplify combining vector layers from different sources.
– Vector data is more compatible with relational database environments, where they can be part of a relational table as a normal column and processed using a multitude of operators.
– Vector file sizes are usually smaller than raster data, which can be 10 to 100 times larger than vector data (depending on resolution).
– Vector data is simpler to update and maintain, whereas a raster image will have to be completely reproduced. (Example: a new road is added).
– Vector data allows much more analysis capability, especially for « networks » such as roads, power, rail, telecommunications, etc. (Examples: Best route, largest port, airfields connected to two-lane highways). Raster data will not have all the characteristics of the features it displays.
k) Non-spatial data
Additional non-spatial data can also be stored along with the spatial data represented by the coordinates of a vector geometry or the position of a raster cell. In vector data, the additional data contains attributes of the feature. For example, a forest inventory polygon may also have an identifier value and information about tree species. In raster data the cell value can store attribute information, but it can also be used as an identifier that can relate to records in another table.
Software is currently being developed to support spatial and non-spatial decision-making, with the solutions to spatial problems being are integrated with solutions to non-spatial problems. The end result with these Flexible Spatial Decision-Making Support Systems (FSDSS)[10] is expected to be that non-experts will be able to use GIS, along with spatial criteria, and simply integrate their non-spatial criteria to view solutions to multi-criteria problems. This system is intended to assist decision-making.
l) Data capture
Data capture—entering information into the system—consumes much of the time of GIS practitioners. There are a variety of methods used to enter data into a GIS where it is stored in a digital format.
Existing data printed on paper or PET film maps can be digitized or scanned to produce digital data. A digitizer produces vector data as an operator traces points, lines, and polygon boundaries from a map. Scanning a map results in raster data that could be further processed to produce vector data.
Survey data can be directly entered into a GIS from digital data collection systems on survey instruments using a technique called Coordinate Geometry (COGO). Positions from a Global Navigation Satellite System (GNSS) like Global Positioning System (GPS), another survey tool, can also be directly entered into a GIS.
Remotely sensed data also plays an important role in data collection and consist of sensors attached to a platform. Sensors include cameras, digital scanners and LIDAR, while platforms usually consist of aircraft and satellites.
The majority of digital data currently comes from photo interpretation of aerial photographs. Soft copy workstations are used to digitize features directly from stereo pairs of digital photographs. These systems allow data to be captured in two and three dimensions, with elevations measured directly from a stereo pair using principles of photogrammetry. Currently, analog aerial photos are scanned before being entered into a soft copy system, but as high quality digital cameras become cheaper this step will be skipped.
Satellite remote sensing provides another important source of spatial data. Here satellites use different sensor packages to passively measure the reflectance from parts of the electromagnetic spectrum or radio waves that were sent out from an active sensor such as radar. Remote sensing collects raster data that can be further processed using different bands to identify objects and classes of interest, such as land cover.
When data is captured, the user should consider if the data should be captured with either a relative accuracy or absolute accuracy, since this could not only influence how information will be interpreted but also the cost of data capture.
In addition to collecting and entering spatial data, attribute data is also entered into a GIS. For vector data, this includes additional information about the objects represented in the system.
After entering data into a GIS, the data usually requires editing, to remove errors, or further processing. For vector data it must be made « topologically correct » before it can be used for some advanced analysis. For example, in a road network, lines must connect with nodes at an intersection. Errors such as undershoots and overshoots must also be removed. For scanned maps, blemishes on the source map may need to be removed from the resulting raster. For example, a fleck of dirt might connect two lines that should not be connected.
m) Raster-to-vector translation
Data restructuring can be performed by a GIS to convert data into different formats. For example, a GIS may be used to convert a satellite image map to a vector structure by generating lines around all cells with the same classification, while determining the cell spatial relationships, such as adjacency or inclusion.
More advanced data processing can occur with image processing, a technique developed in the late 1960s by NASA and the private sector to provide contrast enhancement, false colour rendering and a variety of other techniques including use of two dimensional Fourier transforms.
Since digital data is collected and stored in various ways, the two data sources may not be entirely compatible. So a GIS must be able to convert geographic data from one structure to another.
n) Projections, coordinate systems and registration
A property ownership map and a soils map might show data at different scales. Map information in a GIS must be manipulated so that it registers, or fits, with information gathered from other maps. Before the digital data can be analyzed, they may have to undergo other manipulations—projection and coordinate conversions, for example—that integrate them into a GIS.
The earth can be represented by various models, each of which may provide a different set of coordinates (e.g., latitude, longitude, elevation) for any given point on the Earth’s surface. The simplest model is to assume the earth is a perfect sphere. As more measurements of the earth have accumulated, the models of the earth have become more sophisticated and more accurate. In fact, there are models that apply to different areas of the earth to provide increased accuracy (e.g., North American Datum, 1927 – NAD27 – works well in North America, but not in Europe). See datum (geodesy) for more information.
Projection is a fundamental component of map making. A projection is a mathematical means of transferring information from a model of the Earth, which represents a three-dimensional curved surface, to a two-dimensional medium—paper or a computer screen. Different projections are used for different types of maps because each projection particularly suits specific uses. For example, a projection that accurately represents the shapes of the continents will distort their relative sizes. See Map projection for more information.
Since much of the information in a GIS comes from existing maps, a GIS uses the processing power of the computer to transform digital information, gathered from sources with different projections and/or different coordinate systems, to a common projection and coordinate system. For images, this process is called rectification.
Today, even laypeople are aware of GPS used for locating in terms of latitude, longitude and height. Many people are aware of Google Earth and even GIS. In this scenario, however, majority of us misunderstands latitude and longitude. Authalic coordinates are what generally conceived as latitude and longitude, in which the Earth is assumed as spherical in shape. In day-to-day life, the coordinates we see on maps such as those from GPS are geodetic latitude and longitude. It is also imperative to know the datum of the map in use; and if the datum is changed, any selected location can have different geodetic coordinates.
3. Spatial analysis with GIS
Given the vast range of spatial analysis techniques that have been developed over the past half century, any summary or review can only cover the subject to a limited depth. This is a rapidly changing field, and GIS packages are increasingly including analytical tools as standard built-in facilities or as optional toolsets, add-ins or ‘analysts’. In many instances such facilities are provided by the original software suppliers (commercial vendors or collaborative non commercial development teams), whilst in other cases facilities have been developed and are provided by third parties. Furthermore, many products offer software development kits (SDKs), programming languages and language support, scripting facilities and/or special interfaces for developing one’s own analytical tools or variants. The website Geospatial Analysis and associated book/ebook attempt to provide a reasonably comprehensive guide to the subject.[11] The impact of these myriad paths to perform spatial analysis create a new dimension to business intelligence termed « spatial intelligence » which, when delivered via intranet, democratizes access to operational sorts not usually privy to this type of information.
a) Data modeling
It is difficult to relate wetlands maps to rainfall amounts recorded at different points such as airports, television stations, and high schools. A GIS, however, can be used to depict two- and three-dimensional characteristics of the Earth’s surface, subsurface, and atmosphere from information points. For example, a GIS can quickly generate a map with isopleth or contour lines that indicate differing amounts of rainfall.
Such a map can be thought of as a rainfall contour map. Many sophisticated methods can estimate the characteristics of surfaces from a limited number of point measurements. A two-dimensional contour map created from the surface modeling of rainfall point measurements may be overlaid and analyzed with any other map in a GIS covering the same area.
Additionally, from a series of three-dimensional points, or digital elevation model, isopleth lines representing elevation contours can be generated, along with slope analysis, shaded relief, and other elevation products. Watersheds can be easily defined for any given reach, by computing all of the areas contiguous and uphill from any given point of interest. Similarly, an expected thalweg of where surface water would want to travel in intermittent and permanent streams can be computed from elevation data in the GIS.
b) Topological modeling
Main article: Geospatial topology
A GIS can recognize and analyze the spatial relationships that exist within digitally stored spatial data. These topological relationships allow complex spatial modelling and analysis to be performed. Topological relationships between geometric entities traditionally include adjacency (what adjoins what), containment (what encloses what), and proximity (how close something is to something else).
c) Networks
If all the factories near a wetland were accidentally to release chemicals into the river at the same time, how long would it take for a damaging amount of pollutant to enter the wetland reserve? A GIS can simulate the routing of materials along a linear network. Values such as slope, speed limit, or pipe diameter can be incorporated into network modeling to represent the flow of the phenomenon more accurately. Network modelling is commonly employed in transportation planning, hydrology modeling, and infrastructure modeling.
Cartographic modeling
An example of use of layers in a GIS application. In this example, the forest cover layer (light green) is at the bottom, with the topographic layer over it. Next up is the stream layer, then the boundary layer, then the road layer. The order is very important in order to properly display the final result. Note that the pond layer was located just below the stream layer, so that a stream line can be seen overlying one of the ponds.
The term « cartographic modeling » was (probably) coined by Dana Tomlin in his PhD dissertation and later in his book which has the term in the title. Cartographic modeling refers to a process where several thematic layers of the same area are produced, processed, and analyzed. Tomlin used raster layers, but the overlay method (see below) can be used more generally. Operations on map layers can be combined into algorithms, and eventually into simulation or optimization models.
Map overlay
The combination of several spatial datasets (points, lines or polygons) creates a new output vector dataset, visually similar to stacking several maps of the same region. These overlays are similar to mathematical Venn diagram overlays. A union overlay combines the geographic features and attribute tables of both inputs into a single new output. An intersect overlay defines the area where both inputs overlap and retains a set of attribute fields for each. A symmetric difference overlay defines an output area that includes the total area of both inputs except for the overlapping area.
Data extraction is a GIS process similar to vector overlay, though it can be used in either vector or raster data analysis. Rather than combining the properties and features of both datasets, data extraction involves using a « clip » or « mask » to extract the features of one data set that fall within the spatial extent of another dataset.
In raster data analysis, the overlay of datasets is accomplished through a process known as « local operation on multiple rasters » or « map algebra, » through a function that combines the values of each raster’s matrix. This function may weigh some inputs more than others through use of an « index model » that reflects the influence of various factors upon a geographic phenomenon.
- d) Automated cartography
Digital cartography and GIS both encode spatial relationships in structured formal representations. GIS is used in digital cartography modeling as a (semi)automated process of making maps, so called Automated Cartography. In practice, it can be a subset of a GIS, within which it is equivalent to the stage of visualization, since in most cases not all of the GIS functionality is used. Cartographic products can be either in a digital or in a hardcopy format. Powerful analysis techniques with different data representation can produce high-quality maps within a short time period. The main problem in Automated Cartography is to use a single set of data to produce multiple products at a variety of scales, a technique known as Generalization.
4) Geostatistics
Geostatistics is a point-pattern analysis that produces field predictions from data points. It is a way of looking at the statistical properties of those special data. It is different from general applications of statistics because it employs the use of graph theory and matrix algebra to reduce the number of parameters in the data. Only the second-order properties of the GIS data are analyzed.
When phenomena are measured, the observation methods dictate the accuracy of any subsequent analysis. Due to the nature of the data (e.g. traffic patterns in an urban environment; weather patterns over the Pacific Ocean), a constant or dynamic degree of precision is always lost in the measurement. This loss of precision is determined from the scale and distribution of the data collection.
To determine the statistical relevance of the analysis, an average is determined so that points (gradients) outside of any immediate measurement can be included to determine their predicted behavior. This is due to the limitations of the applied statistic and data collection methods, and interpolation is required to predict the behavior of particles, points, and locations that are not directly measurable.
Hillshade model derived from a Digital Elevation Model (DEM) of the Valestra area in the northern Apennines (Italy)
Interpolation is the process by which a surface is created, usually a raster dataset, through the input of data collected at a number of sample points. There are several forms of interpolation, each which treats the data differently, depending on the properties of the data set. In comparing interpolation methods, the first consideration should be whether or not the source data will change (exact or approximate). Next is whether the method is subjective, a human interpretation, or objective. Then there is the nature of transitions between points: are they abrupt or gradual. Finally, there is whether a method is global (it uses the entire data set to form the model), or local where an algorithm is repeated for a small section of terrain.
Interpolation is a justified measurement because of a Spatial Autocorrelation Principle that recognizes that data collected at any position will have a great similarity to, or influence of those locations within its immediate vicinity.
Digital elevation models (DEM), triangulated irregular networks (TIN), Edge finding algorithms, Theissen Polygons, Fourier analysis, Weighted moving averages, Inverse Distance Weighted, Moving averages, Kriging, Spline, and Trend surface analysis are all mathematical methods to produce interpolative data.
a) Address Geocoding
Geocoding is interpolating spatial locations (X,Y coordinates) from street addresses or any other spatially referenced data such as ZIP Codes, parcel lots and address locations. A reference theme is required to geocode individual addresses, such as a road centerline file with address ranges. The individual address locations have historically been interpolated, or estimated, by examining address ranges along a road segment. These are usually provided in the form of a table or database. The GIS will then place a dot approximately where that address belongs along the segment of centerline. For example, an address point of 500 will be at the midpoint of a line segment that starts with address 1 and ends with address 1000. Geocoding can also be applied against actual parcel data, typically from municipal tax maps. In this case, the result of the geocoding will be an actually positioned space as opposed to an interpolated point. This approach is being increasingly used to provide more precise location information.
It should be noted that there are several (potentially dangerous) caveats that are often overlooked when using interpolation. See the full entry for Geocoding for more information.
Various algorithms are used to help with address matching when the spellings of addresses differ. Address information that a particular entity or organization has data on, such as the post office, may not entirely match the reference theme. There could be variations in street name spelling, community name, etc. Consequently, the user generally has the ability to make matching criteria more stringent, or to relax those parameters so that more addresses will be mapped. Care must be taken to review the results so as not to map addresses incorrectly due to overzealous matching parameters.
b) Reverse geocoding
Reverse geocoding is the process of returning an estimated street address number as it relates to a given coordinate. For example, a user can click on a road centerline theme (thus providing a coordinate) and have information returned that reflects the estimated house number. This house number is interpolated from a range assigned to that road segment. If the user clicks at the midpoint of a segment that starts with address 1 and ends with 100, the returned value will be somewhere near 50. Note that reverse geocoding does not return actual addresses, only estimates of what should be there based on the predetermined range.
c) Data output and cartography
Cartography is the design and production of maps, or visual representations of spatial data. The vast majority of modern cartography is done with the help of computers, usually using a GIS but production quality cartography is also achieved by importing layers into a design program to refine it. Most GIS software gives the user substantial control over the appearance of the data.
Cartographic work serves two major functions:
First, it produces graphics on the screen or on paper that convey the results of analysis to the people who make decisions about resources. Wall maps and other graphics can be generated, allowing the viewer to visualize and thereby understand the results of analyses or simulations of potential events. Web Map Servers facilitate distribution of generated maps through web browsers using various implementations of web-based application programming interfaces (AJAX, Java, Flash, etc).
Second, other database information can be generated for further analysis or use. An example would be a list of all addresses within one mile (1.6 km) of a toxic spill.
d) Graphic display techniques
Traditional maps are abstractions of the real world, a sampling of important elements portrayed on a sheet of paper with symbols to represent physical objects. People who use maps must interpret these symbols. Topographic maps show the shape of land surface with contour lines or with shaded relief.
Today, graphic display techniques such as shading based on altitude in a GIS can make relationships among map elements visible, heightening one’s ability to extract and analyze information. For example, two types of data were combined in a GIS to produce a perspective view of a portion of San Mateo County, California.
- The digital elevation model, consisting of surface elevations recorded on a 30-meter horizontal grid, shows high elevations as white and low elevation as black.
- The accompanying Landsat Thematic Mapper image shows a false-color infrared image looking down at the same area in 30-meter pixels, or picture elements, for the same coordinate points, pixel by pixel, as the elevation information.
A GIS was used to register and combine the two images to render the three-dimensional perspective view looking down the San Andreas Fault, using the Thematic Mapper image pixels, but shaded using the elevation of the landforms. The GIS display depends on the viewing point of the observer and time of day of the display, to properly render the shadows created by the sun’s rays at that latitude, longitude, and time of day.
An archeochrome is a new way of displaying spatial data. It is a thematic on a 3D map that is applied to a specific building or a part of a building. It is suited to the visual display of heat loss data. Spatial ETL
Spatial ETL tools provide the data processing functionality of traditional Extract, Transform, Load (ETL) software, but with a primary focus on the ability to manage spatial data. They provide GIS users with the ability to translate data between different standards and proprietary formats, whilst geometrically transforming the data en-route.
5. GIS Developments
Many disciplines can benefit from GIS technology. An active GIS market has resulted in lower costs and continual improvements in the hardware and software components of GIS. These developments will, in turn, result in a much wider use of the technology[original research?] throughout science, government, business, and industry, with applications including real estate, public health, crime mapping, national defense, sustainable development, natural resources, landscape architecture, archaeology, regional and community planning, transportation and logistics. GIS is also diverging into location-based services (LBS). LBS allows GPS enabled mobile devices to display their location in relation to fixed assets (nearest restaurant, gas station, fire hydrant), mobile assets (friends, children, police car) or to relay their position back to a central server for display or other processing. These services continue to develop with the increased integration of GPS functionality with increasingly powerful mobile electronics (cell phones, PDAs, laptops).
a) OGC standards
Main article: Open Geospatial Consortium
The Open Geospatial Consortium (OGC) is an international industry consortium of 384 companies, government agencies, universities and individuals participating in a consensus process to develop publicly available geoprocessing specifications. Open interfaces and protocols defined by OpenGIS Specifications support interoperable solutions that « geo-enable » the Web, wireless and location-based services, and mainstream IT, and empower technology developers to make complex spatial information and services accessible and useful with all kinds of applications. Open Geospatial Consortium (OGC) protocols include Web Map Service (WMS) and Web Feature Service (WFS).
GIS products are broken down by the OGC into two categories, based on how completely and accurately the software follows the OGC specifications.
OGC standards help GIS tools communicate.
Compliant Products are software products that comply to OGC’s OpenGIS Specifications. When a product has been tested and certified as compliant through the OGC Testing Program, the product is automatically registered as « compliant » on this site.
Implementing Products are software products that implement OpenGIS Specifications but have not yet passed a compliance test. Compliance tests are not available for all specifications. Developers can register their products as implementing draft or approved specifications, though OGC reserves the right to review and verify each entry.
- b) Global change, climate history program and prediction of its impact
Maps have traditionally been used to explore the Earth and to exploit its resources. GIS technology, as an expansion of cartographic science, has enhanced the efficiency and analytic power of traditional mapping. Now, as the scientific community recognizes the environmental consequences of anthropogenic activities influencing climate change, GIS technology is becoming an essential tool to understand the impacts of this change over time. GIS enables combining various sources of data with existing maps map and up-to-date information from earth observation satellites along with the outputs of climate change models. This can help in understanding the effects of climate change on the complex natural systems. One of the classic examples of this is the study of Arctic Ice Melting.
The outputs from a GIS in form of maps combined with satellite imagery allow researchers to view their subjects in ways that literally never have been seen before. The images are also invaluable for conveying the changes due to climate change to non-scientists.
Prediction of the impact of climate change inherently involves many uncertainties stemming from data and models.GIS incorporated with uncertainty theory has been used to model the coastal impact of climate change, including inundation due to sea-level rise and storm erosion.
c) Adding the dimension of time
The condition of the Earth’s surface, atmosphere, and subsurface can be examined by feeding satellite data into a GIS. GIS technology gives researchers the ability to examine the variations in Earth processes over days, months, and years.
As an example, the changes in vegetation vigor through a growing season can be animated to determine when drought was most extensive in a particular region. The resulting graphic, known as a normalized vegetation index, represents a rough measure of plant health. Working with two variables over time would then allow researchers to detect regional differences in the lag between a decline in rainfall and its effect on vegetation.
GIS technology and the availability of digital data on regional and global scales enable such analyses. The satellite sensor output used to generate a vegetation graphic is produced for example by the Advanced Very High Resolution Radiometer (AVHRR). This sensor system detects the amounts of energy reflected from the Earth’s surface across various bands of the spectrum for surface areas of about 1 square kilometer. The satellite sensor produces images of a particular location on the Earth twice a day. AVHRR and more recently the Moderate-Resolution Imaging Spectroradiometer (MODIS) are only two of many sensor systems used for Earth surface analysis. More sensors will follow, generating ever greater amounts of data.
GIS and related technology will help greatly in the management and analysis of these large volumes of data, allowing for better understanding of terrestrial processes and better management of human activities to maintain world economic vitality and environmental quality.
In addition to the integration of time in environmental studies, GIS is also being explored for its ability to track and model the progress of humans throughout their daily routines. A concrete example of progress in this area is the recent release of time-specific population data by the US Census. In this data set, the populations of cities are shown for daytime and evening hours highlighting the pattern of concentration and dispersion generated by North American commuting patterns. The manipulation and generation of data required to produce this data would not have been possible without GIS.
Using models to project the data held by a GIS forward in time have enabled planners to test policy decisions. These systems are known as Spatial Decision Support Systems.
d) Semantics
Tools and technologies emerging from the W3C’s Semantic Web Activity are proving useful for data integration problems in information systems. Correspondingly, such technologies have been proposed as a means to facilitate interoperability and data reuse among GIS applications and also to enable new analysis mechanisms.
Ontologies are a key component of this semantic approach as they allow a formal, machine-readable specification of the concepts and relationships in a given domain. This in turn allows a GIS to focus on the intended meaning of data rather than its syntax or structure. For example, reasoning that a land cover type classified as deciduous needleleaf trees in one dataset is a specialization of land cover type forest in another more roughly classified dataset can help a GIS automatically merge the two datasets under the more general land cover classification. Tentative ontologies have been developed in areas related to GIS applications, for example the hydrology ontology developed by the Ordnance Survey in the United Kingdom and the SWEET ontologies developed by NASA’s Jet Propulsion Laboratory. Also, simpler ontologies and semantic metadata standards are being proposed by the W3C Geo Incubator Group to represent geospatial data on the web.
Recent research results in this area can be seen in the International Conference on Geospatial Semantics and the Terra Cognita — Directions to the Geospatial Semantic Web workshop at the International Semantic Web Conference.
e) Society
With the popularization of GIS in decision making, scholars have begun to scrutinize the social implications of GIS. It has been argued that the production, distribution, utilization, and representation of geographic information are largely related with the social context. Other related topics include discussion on copyright, privacy, and censorship. A more optimistic social approach to GIS adoption is to use it as a tool for public participation.
- The Niger Inner Delta
The Niger Inner Delta forms one of the largest seasonal wetlands in the world, with
a floodplain reaching the size of over 30,000 square kilometers. The delta has great
economic value for local populations, and provides a living for cattle herders,
farmers, and fishermen.
The delta also is of prime importance as a wintering area for several million palearctic
migratory waterbirds, and is especially renowned for the spectacular numbers of
Garganey Anas querquedula and Ruff Philomachus pugnax that can be seen here during
the northern winter period.
In addition, the area is of outstanding importance for both migratory and locally
breeding Afritropical waterbirds.
By contrast with the Senegal Delta, which has been degraded to a catastrophic
degree, the Niger Inner Delta is still largely intact. The only major dam affecting the
area, is the Markala dam near Ségou, which has already been completed in 1947, to
divert Niger water to the rice-growing areas in the Delta Mort, around Niono. The
Markala dam is said (source: ORSTOM) to take only a small percentage of the flood
water, and to have almost no noticeable effect on the height and the length of the
annual flood. In addition the Selingay dam in one of the tributaries in the upper
reaches has a regulating effect on the annual flow, also for a small percentage of the
water only.
The area suffered a considerable amount of degradation during the severe drought
periods in the early seventies and the mid-eighties. These drought periods caused
much damage to natural resources, agriculture, and livestock, which had a serious
impact on the human populations living in the area. Also, several palearctic migrant
birds showed significant population declines. There has been a remarkable recovery
of the resources after a series of copious floods during the nineties.
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6. Evapotranspiration
a) definition
For memory : evapotranspiration is deined by the return of water vapour to the atmosphere by evaporation from land and water surfaces and by the transpiration of vegetation
The evapotranspiration corresponds to the quantity of total water transferred by the ground towards the atmosphere by the evaporation at ground level and by the perspiration of plants. She(it) corresponds to the flow of latent heat in the balance sheet(assessment) of energy:
Rn ( clear(net) brilliance(radiation)) + a Hour (F of sensitive heat) + THE ( ETR) + G (F of heat in the ground) +? CO ² +? Mr. = 0 (delta being very low(weak) towards the other sensors).
The used symbols are American.
The clear(net) brilliance(radiation) is measured by a pyrradiomètre. The flow of heat in the ground is measured by a fluxmètre. The latent and sensitive flows of heat are calculated from differential measures of ambient and wet temperature of placed psychromètres th > AND < / math >.
She can be potential ( ETP), or real ( ETR).
She can be maximum ETM = ETm = ETP x Kc (Kc being a farming coefficient) The ETP is either measured, or calculated from diverse meteo data (wind speed, hygrometry, temperature, etc.).
There are several methods of calculation (Turkish ETP, ETP Penman-Monteith).
The ETR corresponds to the latent flow of heat of the balance sheet(assessment) of energy calculated over a végètal place setting. The devices of calculation of the ETR were the object of the patent(certificate): U.S. Obvious no 4 599 889 [ 1 ]. The devices which were industrialized in France from this patent(certificate) are essentially BEARN and SAMER S Mr. used in HAPEX MOBILHY ( 1986 ) and in the United States the station(resort) AquaSaver. Prize-winner of the Ministry of Research in 2001, Christian de Pescara proposed a new device allowing to answer the questions: how much water (accumulated ETR all 24 h)? When is it necessary to irrigate (temperature of surface)? The knowledge of the ETR is essential because it translates the interaction of the hydric complex: ground-Plante-climat
- b) Diverse expressions of the evapotranspiration
ETp: it is usually defined as the sum of the evaporation by the surface of the ground and the perspiration by the foliage of a culture stomates of which is completely opened, when the ground supplies all the wanted water. It is a theoretical value, calculated by formulae from measures on a meteo park.
This notion of potential consumption in water was introduced by Howard Latimer Penman in 1948. In France the potential evapotranspiration is calculated on a fescue herd of bulls (lawn 7 cms in height), covering completely the ground, fed well with water, with active phase where are realized the meteorological measures. A comparative study of growth and within a big enough plot of land.
THE ETp depends only on a particular culture where are realized the meteorological measures. A comparative study of the various formulae was realized within the F.A.O. (Food and agriculture(farming) organization of the United Nations) by the I.NI.A in Portugal. The calculations realized over several years demonstrate a strong difference.
ETo: reference evapotranspiration. It is a limit of the ETp used for practical reasons. As reference, it is measured and calculated on the considered plant place setting. THE ETo thus corresponds to a potential evaporation in real hydric conditions. Certain climates, less moderated than Great Britain, do not allow to maintain this reference fescue, in particular in California for the network CIMIS
ETM: maximal Evapotranspiration. It is the maximal value of the evapotranspiration of a culture given, at a vegetative stage(stadium), in climatic given conditions, taken into account by the ETp. It is a correction of the ETp according to the plant place setting. ETM = Kc x ETP, Kc being the farming coefficient. To determine the farming coefficient, Christian de Pescara proposes the following method: it is necessary to lead(drive) the culture to the ETM which we can determine by a device calculating over the plot of land the ETR or by a lysimètre. Then we have ETRmax = ETM and we calculate: Kc = ETRmax / ETp. So we can calibrate the culturaux coefficients Kc.
- c) Units of measure and orders of height of the ETp
As for the measure of the precipitation, the unity(unit) is the mm in height of water. 1 mm correpond in 1 liter per square meter or in 10 cubic meters by hectare. THE ETp can reach(affect) 4-6 mm / day in height be in European temperate zone and 6-8 mm / day in Mediterranean zone.
- Inner Nigger delta
The Inner Niger Delta, also known as the Macina or Inland Niger Delta, is a large area of lakes and floodplains in the semi-arid Sahel area of central Mali, just south of the Sahara desert.
An easily flooded plain, it is the site which is a part of what we call wet zones. In Africa, there are about twenty large-scale wet zones, that is consequent enough in ecological, economic and social term so that the state on which she(it) depends and the international reference bodies on it préoccupent*. Some are situated on the coast, it is in particular about lagoons or about mangrove swamps, and the others extend inside lands; they are generally plains flooded by rivers and stream. They are very rich on the ecological plan(shot), – fauna and flora abound-, and are characterized by big biodiversity. From the point of view of the exploitation(operation), we are in the presence of three systems of production: peach(fishing), breeding, agriculture(farming).Very rich also on the human plan(shot), the populations nomads and home-bodies meet there. A continual coming and going of sinners, breeders, farmers according to the height of water, and thus according to the seasons practices then(is then applied). So when the plain is in water, the fishermen invest(surround) places. When the water withdraws, come then to the same places the breeders transhumants, of peule ethnic group for the greater part. Finally, on the islands of earth(ground) or in border of the easily flooded zone, we find some villages installed(settled) by home-bodies.
The internal delta of the river Niger: the floods and the Man
The internal delta of the river Niger establishes(constitutes) a strongly exemplary case. Of a surface of 40 000 hectares in maximal flood it is the vastest wet zone of Africa. All the more private individual as her works still in a very natural way. Let us hear(understand) there that this delta was, until now, little fitted out by the man and that its hydrological functioning is still very natural Indeed, the site does not have – or little – undergone by considerable modifications by the construction of works or by the arrangements(developments), the vocation of which would be to master the height of the river Niger and the surface of flood by the release of artificial floods.
The recent hydrological searches(researches) show however that the site undergoes more strongly that it appeared to it the effects of the dam of Sélingué, situated indeed upstream (approximately in 600 km of the entrance(entry) of the delta). The case is exemplary also for demographic reasons. The delta is a zone enough populated – by the man and by the fauna of the most varied – so that the observer can learn from it on the complex realities of the link man-nature in a region in the middle changing
The organization of the production
According to his characteristics of easily flooded zone, the internal delta of the river Niger saw developing a human activity propped up on the rhythm of the floods. Activity organized around three systems of production: peach(fishing), breeding, agriculture(farming). Peach(fishing) when the water is present, agriculture(farming) and breeding when the water withdraws and gives way to fertile and for a long time wet soils. A change of activity which pulls(entails) a movement of ethnoprofessionnels groups, each specialized in the exploitation(operation) of a resource.
The changes, the adaptation to the changes and the development.
When the environment makes rougher … If the man, contrary to the other waterside zones of the river Niger, little intervened by big arrangements(developments) (as in the zone said about the Service(Office) of Niger, more upstream, in southwest) the environment underwent all the same, these last decades, modifications. We think in a first place, in the climate. With the big drought which raged in all Sahel from 1974 and which settled down in a recurring way in the 80s, the balance which assures(insures) the renewal of the resources saw itself seriously pushed aside(knocked down). We notice that since this time(period), there is less water in the delta. The floods last less for a long time, the water rises less high and withdraws more quickly than before. The flood thus covers a lesser surface of cultivable ground or pâturable. In hydrological and climatological term, this trend(tendency) would look inexorable, even if punctually the river reserves some surprises. Year 1994, for example, knew an exceptionally high level of floods, to the surprise of the inhabitants of the delta. Many floods, and with them, lost harvests, of the bathed cattle, destroyed(annulled) villages, and an epidemic of cholera which killed several hundreds of persons, first of all of children.
The level of the low tide, in dry season, is artificially maintained by releases since the dam of Sélingué, upstream to Bamako, in about six hundred kilometers of the entrance(entry) of the delta, towards Djenné. This dam assures(insures) the supply electricity of the capital, since 1981. Without these releases, the river would very probably have been flat broke several times during the 80s and 90. The vigour of rainy season upstream, in the South of the sahélo-Sudanese zone is doubtless the main reason of these strong floods, which did not have, since of equivalent in the delta.
The men(people) had to adapt themselves and, understand(include) little by little that the balance parking of harmony and well-being is well and truly precarious. Less water less for a long time, it wants to say fewer places of peach(fishing), but also fewer sprayed lands which give good pastures and good grounds to cultivate. To survive without having to leave the delta, both opted for the diversification. The fishermen at the same time begin cultivating, irrigating there where, before, they found some water naturally. The small breeding developed well. Goats(tackles), sheeps(muttons), poultry, assure(insure) of what to enrich the dish(flat) of rice or thousand when the carp, the silurid or better: fat and delicious captain are running out. A good many of villagers or nomads opted for the city and its multiple professions. They go a few months there, between two seasons of peach(fishing). Today, the theme of the diversification is for the agenda of a lot of rustic meetings, which are livened up(led) or not by associations of development aid.
- a) Location and description
The delta consists of the middle course of the Niger River, between the bifurcated Niger and its tributary, the Bani, which from here run north towards the desert. The Niger is the longest river in West Africa. Towns such as the river-port of Mopti, Sévaré and Djenné, with its mud-brick Great Mosque lie in the 400 km-long region.
The Fulani and Dogon inhabit the Macina region and the surrounding area, which has a population of over 500,000. Most of the year the area has a hot and dry climate, with hot winds from the nearby Sahara raising the temperature up to 40° C. During the wet season, which lasts from July to September but lasts longer the further south you go, the swamp floods into a lake and naturally irrigates the land. When the dry season comes, the Macina turns into a network of lakes and channels. Cattle, pearl millet, and rice are its important agricultural products. The Macina inland delta also provides water and fish for the Malians living there and during the wet season is a haven for large numbers of birds.
Due to its proximity to the widening Sahel, there have been concerns that the Macina may be getting less rain every year.
In the early 19th century, Seku Amadu founded a Massina Empire in the region, building a capital at Hamdullahi in 1820. The Massina fell to El Hadj Umar Tall’s Toucouleur Empire in 1862, who in turn fell to the French army. The region became a part of the country of Mali on its independence in 1960.
- b) Ecology
The Niger inland Delta lies in the Sahelian zone, and has an ecosystem that is largely dependent on the amount of flooding it receives.[
Precipitation in the water basins of the upper course of the Bani and Niger rivers makes for rising waterlevels downstream. The rising water floods varying parts of the low-level delta area, with the water rise determined by the amount of rain fallen upstream. This in turn, is influenced by the northward movement of the Intertropical Convergence Zone. A delay exists between the peak amount of precipitation and the maximum water level in the inland delta area. While the wet season lasts three months from July till September, the western and southern edges of the delta area are not flooded until early to mid-October. Consequence is that parts of the delta are flooded while the dry season is well under way. Note that only the lowest patches are flooded annually: higher elevations receive flooding in more intermittent periods due to the changing degrees of waterlevel rises. This division in roughly three zones (flooded, periodically flooded and not-periodically flooded), makes for patches that vary in their nature according to their proximity to a main body water and elevation.
In turn, this strongly affects land use in and around the inland delta, as human impact is driven by agriculture, both irrigated and rainfed, grazing and browsing of herds and flocks and the collection of wood for fuel, all dependent on the availability of water
- Threats and preservation
Three Ramsar sites, a total of 1,620 km2 have been declared in the delta; Lac Horo, Lac Debo, and the Séri floodplain. But the delta is largely unprotected and at the same time fishing and farming in the delta is vital to the livelihoods of the people of Mali. Low water levels in the rivers, lack of rain, increasing human population and a break-up of the traditional tribal arrangements for sharing the resources of the delta are all factors that may contribute to severely damaging the ecosystem. In particular fishing is less regulated (in the past only two tribes were permitted to fish) and fish stocks in the rivers are declining. In a similar way lack of control is also causing over-grazing. Finally the Selingue Dam and other water control projects affect the levels and seasonal behaviour of the rivers.
8) Modelisation
The lakeside basin of Niger, and its internal delta, establishes(constitutes) a particular hydrosystem characterized by its numerous effluents, lakes and plains of flood on one hand and by Sahelian climatic conditions and semi dry on the other hand. The columns(chronicles) of the upstream contributions and the exits(releases) approval of the internal delta show that the annual losses, owed essentially to the evaporation, vary from 40 km3 to 6 km3, that is 47 % of entrances(entries) to wet period and only 32 % in period dry, because of the reduction of the flooded zones. The search(research) for a model of the spatiotemporal extension of the flood in the internal delta leads(drives) to consider that the annual maximum of the flooded surfaces varies 35 000 km2 in wet period in 7 000 km2 in dry period.
NTRODUCTION Vast zone of manuring of the contributions of Niger, the lakeside basin established(constituted) by an easily flooded internal delta and a system gives a complex of lakes in right bank and left bank covers a surface of more than 50.000 km2 following a directed rectangle SW.NE 450 km in length on 125 km in width The hydrological functioning of the lakeside basin of the river Niger is widely dependent:
– exogenous conditions of flow, the main part of water ressources resulting from regions much more sprayed with the upstream and thus the diets(regimes) hydroclinmatiques of the superior ponds of the river Niger and of Bani;
Morphological and climatological conditions appropriate(clean) for the internal delta, governing the flows (dèfluences, floods) and the hydrological balance sheet(assessment) (evaporation, infiltration).
ELEMENTS OF the GOVERNED ME HYDROLOGIC IN THE BASIN LACTUSTRE
From the point of view of the climatic conditions, the station(resort) of Mopti has a representative geographical situation of the South and the center of the lakeside basin; the station(resort) of Timbuktoo characterizes the North of the basin. The taken into account parameters are the temperature and the relative humidity The diet(regime) of the precipitation corresponds for the south part(party) of the central Delta to the Sahelian diet(regime); the North of the basin is subjected to the subdesert diet(regime). The updated averages create on the whole region a decline to the south of the precipitation from 120 to 150 mm with regard to the averages previous to the drought. So the height of interannual haste is crossed(spent) â Mopti from 535 mm to 415 mm
The flows in the lakeside basin get organized around a complex river system of effluents, défluents and lakes which were besides described. We call back(remind) below the main axes of flow (Brunet-Moret and al, on 1986; Gallais, on 1967).
J,) upstream and central Delta downstream to K-Macina for Niger, of Douna for Bani with constitution of two major branches.
- the main arm of Niger which passes in transit of the South in the northeast until Mopti where it receives Bani then joins the Lake Débo.
- the secondary arm of Diaka, effluent of Niger at the level of Diafarabé measured to Kara, his(her,its) annual debit(flow) corresponds to the third(third party) of the debit(flow) of Niger to Ké-Macina. He joins the lake Débo after the crossing of Walado.
Tributaries of lesser importance in left bank of Niger between Tilembeya and Mopti return through the central part(party) of the delta a not insignificant part(party) of the flows towards the Diaka_ En left bank of Bani, the other effluents join Niger through complex Djenné-Kouakourou, what explains the important losses of Bani between Douna and Sofara.
- North basin, of the Lake Débo to Say with three main draining Luxuries · Issa Ber, major branch on the West which assures(insures) the transfer of 80 % 87 %/e exits(releases) of the lake Débo, respectively in wet and dry periods. The reference station(resort) is the one of Akka_ Il feed the lakeside system of left bank (region of Léré and lakes Fati and Horo).
- Bara Issa concerned from 10 % to 12 % of the flows following the low(weak) or strong hydraulicité of Niger. The debits(flows) are measured to Awoye. He joins Issa Ber upstream to Diré.
- Kolikoli, the défluent smallest of the Lake Débo exports from 3 to 10 % exits(releases) of the Lake Débo, towards the Lake Korientzé, before joining Bara Issa to Saraféré, + Bara Issa and Kolikoli feed, in good conditions of hydraulicité, the vast lakeside system of right bank (lakes Korarou on lakes Nangaye, Garou, Hariboma etc.)
- 3) The north extremity of the lakeside basin, to Say to Korioumé ( Timbuktoo) is especially marked by the effluent of the oxbow lake of Goundam feeding the lakeside Télé-Faguibine system. Niger reached(affected) then its ultimate route(course) northward and approach the buckle of Niger with the hydrological control of the threshold of Tossaye. From Ké-Macina to Diré, Niger crossed(went through) approximately 550 km n and lost only 12 m of height, that is an average slope of 2,2 cms by kilometer.
The superficial slope of Niger in high waters is of the order of 2 cms / km between Mopti and Niafounké but grave to 1 cm / km of Niafounké to Diré. Upstream to the Lake Débo, she(it) reaches(affects) 3 cms / km (Lamagat and al, on 1983; Guiguen, on 1985).
These low(weak) slopes pull(entail) maximal speeds of the on-surface current not exceeding(irritating) 0,3 – 0,6 m/s in the main arms. The hydraulic conditions make particularly delicate the measures of debit(flow) and evaluations of the traffic(circulations) of water in the Central Delta, especially at the level of secondary effluents where speeds are often imperceptible.
For three years-type(-chap) (wet, average and dry) the annual average debits(flows) in the main stations(resorts) of Koulikoro, Douna and the Delta. Year 1954 corresponds in a wet year of cinquantennale frequency; .1968 is very nearby the average and 1985 has a frequency cinquantennale dry.
The examination of modules shows that the flows checked(controlled) in the entrance(entry) of Diaka and after the confluence Mopti-Bani have already lost approximately 18 %, 14 % and 6 % of the initial contributions, as we have a strong, average or low(weak) floods. The losses are all the more important as the zones of floods increase, also denied that the secondary effluents transfer more important volumes. With regard to entrances(entries), the modules of Diré lost approximately 47 %, 37 % and 32 %, the strong floods to the low(weak) floods.
It is naturally these losses and their scale that make the hydrological characteristic main of the lakeside basin and, this one, a tremendous machine évaporatoire in western Africa. The column(chronicle) of these annual losses expressed there km3 was compared with that of the entrances(entries) to the basin Iacustre. One of the other important characteristics of the hydrology of the Delta likes in the amortization(depreciation) of the annual floods. L spreading of hydrograms, established from the monthly debits(flows). Amortization(depreciation) in the time(weather) and gap of the maximum towards the approval.
For rather comparable hydraulic sections, the amplitude of the maximal heights of dry and wet ten-year floods is about 100 cms for the stations(resorts) of Ké-Macina, Mopti and Diré, for the corresponding amplitudes of debit(flow) of 1700, 1000 and 700 m3/. The median maximum of floods (Q ~, u\x) was estimated at 5600 m/s. For KéMacina, 1600 m3 / for Diaka to Kara, 3300 m/s for Niger to Mopti and on 2300 nor ‘ for Niger to Diré. Reports(connections) Q, x / module cross(spend) respectively 4,7 in 4, then 2, 9 and 2,3 for these four stations(resorts).
The evolution of the volumes of the annual contributions of the upper pond in billions of m3 ( km3 ) measured on Ké-Macina and Douna and losses corresponding to the approval of the Central Delta ( Diré).
The time(weather) of distribution of the wave of floods is very variable; he(it) is long all the more as the maximum of floods is important but it is not possible to establish of precise relation. The distribution of the maximum of floods is all the slower as the flood and the overflowing become important. Between the minimal and maximal floods, the transfer of the wave of floods can vary from 18 days to 78 days between Ké-Macina and Diré.
On three main sections, KéMacina-Mopti ( Nantaka), Nantaka. – Akka and Akka – Diré, the wave of floods is the slowest on the section Mopti-Akka. Let us specify that we do not have to confuse(merge) speed of the wave of floods and speed of the current. The dates of appearance of the maximum of floods are also very variable: on average ler in October to Ké-Macina, in October 24th to Mopti-Nantaka and in January 4th to Diré. This big variability explains the extreme complexity of a modelling of the flood in the Delta
COMPARISON OF THE HYDROLOGICAL CONDITIONS IN THE DELTA IN WET PERIOD AND IN DRY PERIOD
Two periods of five years were taken into account; the one, from 1962 till 1966, is situated during the wet « cycle » of Niger without expressing the maximal values; other one, from 1982 till 1986 is widely overdrawn and understands(includes) the most overdrawn year of the series ( 1984 ). The comparison is made between the averages of these two periods to bring to light the main lines of the evolution of the hydrological functioning in you Delta
The information was treated(handled) in the step of monthly time(weather) for the whole hydrological information; the volumes are expressed km3 there. At the level of entrances(entries), the most characteristic fact likes in an impoverishment of water ressources much more marked on Bani than on Niger: the modules of Bani are in the report(relationship) of 5,3, against 2,2 for those of Niger. In wet period, the maximum monthly debit(flow) is the one of October for Bani and Niger; in dry period, both streams have their monthly maximum debit(flow) in September, at a level obviously much less high.
This pseudoprecocity of the floods corresponds in fact to a hydrogram of floods truncated in volume and at time(weather) by the effects of the drought. The annual flows of Diré and Tossaye shows between periods wet ( H ) and sandbank (s) of the respective reports(connections) of 2,14 and 2,10, on the whole very nearby of the report(relationship) of Niger to Ké-Macina. The gap between the monthly debits(flows) of floods is more important because he is respectively supposed to be for Diré and Tossaye of December and January (H) in October and November (S)
Hydrograms of the monthly debits(flows) of the upstream contributions (Ké-Macina + Douna) and exits(releases) approval of Diré and Tossaye showing the amortization(depreciation) of the wave of floods in the Delta for wet period, on 1962 – 66 and a dry period, on 1982 – 86 The study of the annual losses shows that we cross(spend) 29 km3 between entrances(entries) and to Say for wet period, in 7 km3 for dry period is a report(relationship) of 4,14. Between Diré and Tossaye, the losses are much more reduced: about 3 km3 in wet period, 1 km3 in dry period (report(relationship) of 3) .1l is important to underline that the report(relationship) of 4 expressing the decrease of the losses in the Delta also translates the decrease of the spatiotemporal extension of the flood.
The balance sheet(assessment) of the « losses » in the step of monthly time(weather) shows a first period of progress of the flood with losses corresponding to the infiltration, to the evaporation and especially to the storage of important volumes in the plains of flood. This first period reaches(affects) its maximum in September and October for wet years (14 km3 in October) and in September for dry years, with a little less than 5 km3 of losses. The trapping of waters decreases quickly in November ( H ) and in October () and then a period of partial return(restoration) of the booby-trapped volumes appears. It is the draining of the plains of flood. In wet years, the months of very strong return(restoration) are the ones of December, January, February with a maximum in January of the order of 3,4 km3. The return(restoration) is more premature but much more low(much weaker) in dry years: around 1 km3 in November and December. This destocking concerns obviously only the zones of flood in contact with the river system; there is gradually cut between certain low zones or puddles and the river, the residual volumes passing in the balance sheet(assessment) évaporatoire of the region. The evolution very contrasted in dry and wet periods of this phase of diminution doubtless establishes(constitutes) the major explanation of the evolution of the halieutic production (Laé, on 1992).
Monthly average variation of the volume of the losses between Ké-Macina-Douna and Diré and between Diré and Tossaye for wet periods (on 1962 – 66) and dry (on 1982 – 86), in billions of m3 ( km3 ). The negative values correspond to a return(restoration) in the river system of volumes stored in the plains of flood. The month 9 of the hydrological year is May
The monthly volume of the losses or the returns(restorations) between entrances(entries) and Diré and the debit(flow) of entrances(entries) to Ké-Macina and Douna indicates allows to follow the evolution of the functioning of the Delta. We indeed observe, for both series of years, the same type(chap) of curve in buckle passing by the phase of return(restoration) but the difference of amplitude of two periods is particularly striking.
The evapotranspiration on free groundwater was estimated(esteemed) from the potential evapotranspirations calculated by the formula of Penman on the stations(resorts) of Mopti and Timbuktoo affected(allocated) respectively by a spatial level-headedness of 0,67 and by 0,33. The difference between wet years ( 1962-66 ) and dry (1982-86) is hardly significant on the scale of year, with 2260 mm mean values and 2360 mm. The evaporations of the months of strong flood are very nearby in particular (Pouyaud, on 1986).
After getting in touch between the monthly average losses observed to Diré ( km3 ) and the debits(flows) entered by Ké-Macina and Douna in wet years ( 1962-1966 ) and dry (1982-1986) (the month 6 is October) For the same periods, the average heights of monthly precipitation were calculated from the statements of nine stations(resorts) of the Basin (Ké-Macina, San, Tenenkou, Sofara, Mopti, Sah, Saraféré, Niafounké, Say). The annual total for considered wet period is 490 mm and 330 mm for dry period. The total monthly magazine of August is the most affected(allocated) for the dry period considered (half of the value of wet period)
ESTIMATE(APPRAISAL) OF SURFACES FLOODED IN THE INTERNAL DELTA
The seasonal follow-up of the losses between the debits(flows) of entrance(entry) to the internal delta and the debit(flow) of exit(release) to Diré put in evidence of the phenomena of storage then return(restoration) of important volumes in the zones of flood; the annual balance sheet(assessment) of the losses is a good indicator(informer) of the extension of the flood, the losses being for the main part consumed by evaporation.
In the hydrological balance sheet(assessment) of the central Delta also intervene the precipitation and the infiltration. Previous studies showed that in the transition of the end of dry season, the losses were unimportant in the balance sheet(assessment), what means that the infiltration – and the food(supply) of aquifers – is mainly made through the flooded surfaces. Only the precipitation received by the system in water participate in the balance sheet(assessment); infiltration and resumed(taken back) by evaporation of the precipitation, absence of significant streaming on zones outside water exclude these of the balance sheet(assessment).
The hydrological balance sheet(assessment) can amount by the following equations in which the various terms are returned to volumes:
PERTES V) =DEBIT UPSTREAM ( Vm) – DEBIT(FLOW) AVAL V) = (EVAPORATION (E) + INFILTRATION I) + STORAGE (flood) (St)) – (PRECIPITATION (P) + the OTHER STREAMED CONTRIBUTIONS (r) + RETURN(RESTORATION) (Rs)) Three main periods:
1 °) rise in the water level positive Losses = E + I + St – P – r – Rs r and unimportant Rs = E+I+St-P If is the main term
2 °) maximum of the floods Losses = E + I + St – slack Rs of the flood St = Rs LOSSES * EVAPORATION
3 °) decreased : Negative losses = E + I – Rs
ANNUAL BALANCE SHEET(ASSESSMENT)
Losses = E + I + dSt – P by hypothesis I = P, except for very wet years, dSt is unimportant where from Losses = E Dans the evaluation proposed here, we shall suppose that the terms infiltration and haste on surfaces in water are the same order of height; the precipitation compensate for the infiltration in the annual balance sheet(assessment) and the total losses can be likened to the balance sheet(assessment) évaporatoire of the flooded zones
Another simplifying hypothesis consists in imagining a homogeneous functioning of the hydrological system between the south and north zones of the delta and in supposing that the curve of the losses shows at the moment. T (that is tmax) characteristic for whom(which) the flood reached(affected) its maximum: there is no more storage and not still return(restoration). We are in situation of slack, the losses correspond to the only evaporation. This characteristic point coincides naturally with the maximum of the floods. The moment t chosen is the one of the maximum observed to Mopti-Nantaka. On the basis of these hypotheses, three years-type(-chap) (wet, average and dry) were studied. The graph of the monthly losses and the date of appearance of the maximum to Mopti allow to determine the monthly loss, centred over the moment tmax, due to the evaporation and to estimate(esteem) the maximal surface of corresponding flood (= V/E).
The estimation of the surfaces of flood of the months framing(supervising) the monthly maximum of flood is obtained from an evaluation by successive estimates of the monthly losses by evaporation, based on the progress of the rise in the water level then the diminution and so that the annual balance sheet(assessment) of the evaporation corresponds to the hydrological losses. Month a month, the surfaces of flood are then deducted from respective values of the monthly evaporation. The model was applied to the whole available column(chronicle) to estimate(esteem) every year the surfaces of the month of maximal flood. After study: the surfaces of maximal flood were correlated in the volumes of entrances(entries), in the annual losses and in the maximal height of the floods to Mopti-Nantaka. The regressions are all good quality, the parameter « entrances »(« entries ») are however the most relevant.In terms of forecasts, the accumulation of the contributions stopped(arrested) in the date of the maximum of the hold establishes(constitutes) a good parameter of estimation of the maximal surface of flood
CRITIC(CRITICISM) OF the MODEL AND THE SPATIOTEMPORAL EXTENSION OF THE FLOOD
The results(profits) show for the years of strong hydraulicité overestimated values if we refer to the estimations made on card(map) of the maximal extension of the flood for the contemporary period, closer to 35 000 than to 40 000 km2 to Diré. The model is thus more adapted for them very high tides. The filling of the remote lakeside systems pulls(entails) important losses of volumes the exhaustion of which by evaporation can ask several years. Besides, the basic hypotheses simplify too much the functioning of the Delta the complexity of which we saw, there is necessarily gap between the upstream part(party) of the delta and the part(party) approval;The notion of slack of the maximum remains very theoretical: the flood still progresses in the margins of the low plains when the diminution is already begun(primed) on the main axes of flow, and it is true all the more as in strong hydraulicité, the stake in water of the lakeside system of right bank appears late. Finally, the estimations of the evaporation remain to verify; although they are the same order of height as on the lake Chad (2200-2300 mm the year ‘), situated in a comparable climatic context; they ask to be specified by measures in situ
That is he(it) of the evapotranspiration of bourgoutières, ricefields and vétiveraies?
Be that as it may, the proposed determinations establish(constitute) an acceptable estimate of the maximal surfaces of flood in the conditions of hydraulicités average and low(weak).
For the studies of halieutic production (Laé, on 1992), we prefer generally, in the maximal extension of the floods, to use a parameter of spatiotemporal extension of these concerning several months. The criteria of definition of such parameters stand out(go out again) from the choice of the operator and from its objectives.We can however propose here a simple method based on the analysis which has just been presented. The graph of the evaporated monthly volumes can be returned to a triangular diagram the height of which corresponds to the 5TH maximal evaporated volume centred on tmax. The basic time(weather) (you) of this diagram is then defined in month by the equation your = 2 ( annual / VE Losses)
We shall deduct easily the duration from it of the flood ti of which the extension If is superior or equal to a proportion chosen the maximal extension of flooded surfaces SM, X; the monthly evaporation varying enough little from August till February – The main part of the period of flood – the reserved report(relationship) (KS = Si / SM2X) can be directly used in the expression ti = (I – Ks) tB
It is necessary to specify that this method does not bring earnings(gain) of information with regard to the use of variables annual Losses and SM. But only a more concrete representation of the spatiotemporal extension of the flood.
So, with a report(relationship) of 0,5 applied to the maximal surfaces of flood for the years-type(-chap) of the initial model, we would have:
- For 1954 If > _ 21 500 km2 during ti = 5,4 months (160 j) – for 1968 Yes? 12 000 km2 during t; = 4,5 months (135 j) – For 1985 If _ > 9 000 km2 during t; = 2,7 months (80 j)
The method also lends itself to the calculation of the minimal surfaces put in water ( Sd) during a definite duration, td:
- With Kt = td / tn we have Sd 3 (1 – Kt) SMax During a duration your of 4 months, we would have had a minimal surface flooded with 27 000 km2 in 1954, with 13 300 km2 in 1968, with 4 700 km2 in 1985.
FORMULAE OF EVAPOTRANSPIRATION
Given the importance which takes the irrigation in the world, he(it) is useful of know the quantities of water to be brought to the cultures. Any calculation of network of irrigation must be based on an estimation of the evapotranspiration by means of climatic data, if only for know, after realization, the losses by infiltration.
Several climatic formulae were tested. After elimination of some (as the formula of Thornthwaite (1), According to the climatic data which we have, we can use(get) the one or the other one. Tables allow easy calculations. We gave our appreciation in some words onto these formulae according to diverse experience(experiment). Tanks Colorado, lysimètres, calculation of the deficits of rivers, measures of humidity in grounds, measure of the quantity of water used for the irrigation, will allow to test the proposed formulae
FORMULAE OF EVAPOTRANSPIRATION I – KNOWING THE SUNSTROKE N
n number of hours of sunstroke measured in the solarigraphe Campbell.
N theoretical number of hours according to the latitude and the time(period) of the year.
(1) Formulae the most used until now, of Thornthwaite and Blaney-Criddle, based especially on 1a air temperature, express very badly the monthly variations of the evapotranspiration. The solar radiation (especially for the evaporation of the free water) or even the deficit of saturation of the air(sight) (evapotranspiration of plants) are the most important climatic elements.
On the other hand, the formula Thorntwaite is generally valid in annual data and can very well be of use to the establishment of a climatic card(map).
- Among these nine formulae, we recommend particularly, when their calculation is possible, the following formulae: Penman, Businger, Walker, Turk and Prescott. Walker and Turk are the easiest to calculate, with a preference for the first one(night) which
- Turk’s formula is / relative Humidity > 50 % (average of the month)
E T mm / 10 days = 0, 13t / (t + 15) (Ig + 50)
- E Tp mm / month = 0, 40t / (t+15) (Ig + 50)
E Tp = potential evapotranspiration in mm
t = temperature averages of the month °C
Ig = real global radiation in small calories by cm2 of horizontal surface and a day, during the considered period.
= IgA (0, 18 + 0, 62 n/N)
IgA is given by tables: it is the theoretical global radiation, without cloud in the considered latitude (see table IgA or RA) (For February, replace 0, 40 by 0, 37)
Relative B B/Humidité < 50 %
E Tp /mm/mois = 0.40 [t / (t+15)] (Ig + 50) (1 + (50 – relative humidity)/70)
(For February, replace 0, 40 by 0, 37)
Notes: this formula is good, but empirical, and does not enough take into account the humidity of the air(sight) in dry region..
- Walker’s formula It is a simplification of the formula of Penman
E = [(1 – u – r) Rl] (1 + d/D)-1
For tank of evaporation, by supposing 7 %, of reflection of the light ( albedo ), we obtain
Eo = 0,
Eo=93 R1 (1 + d/D)-1 to calculate the potential evapotranspiration, by supposing 20 % of reflection for the vegetation ( r ) and 1 % for the photosynthesis ( N ); we obtain
ET = 0, 83 Eo On adopt R1 = RA (0, 20 + 0, 48 N) where from Eo = 0,93 RA (0,20 + 0,48n / N) ( 1+d / D )-1
R1 = the true global radiation RA = theoretical global radiation Eo = evaporation in mm of a tank of water ET » potential evapotranspiration in mm 93 RA is given by a table in equivalent of mm of water d is a psychrométrique constant * 0, 49 D is the slope of the curve of saturation of vapor according to the témpérature (1 + d/D) 1 is given by a table according to the average temperature of the month.
To know n/N and T Note is thus enough: good formula stemming from a theoretical formula after simplification; we can bring in the albedo of plants, to calculate the evapotranspiration of a given culture (to see value of albedo in tables.)
2 – KNOWING THE HUMIDITY OF THE AIR(SIGHT), WITHOUT THE SUNSTROKE
1 °) Prescott Avantages’s formulae : take into account at once(at the same time) the temperature, the humidity of the air(sight) and the considered culture.
2 °) Formula of Haude Ew=11,5x (E-e)
Ew evaporation in mm a month of a free groundwater
E – e = deficit of saturation in mm Hg, but taken at 2 pm and in 2 m of the ground.
Evaporation a day = 0, 37 (E – e)
Note Advantage avoid making calculations of averages d humidity
Inconveniences: less faithful than Prescott, because can be disrupted(perturbed) by local conditions of humidity of the air(sight) at 2 pm.
As for Prescott, the daily factor(mailman) can vary from 0,26 to 0,39 (more low(weaker) in dry climate, ‘ stronger in wet climate).
- KNOWING THE DIFFERENCE ENTER DRY THERMOMETERS AND WET
Olivier’s Formulae
Advantage: easy to calculate, from the common(current) climatic data.
Inconvenience: the evapotranspiration in dry country exagére.
- KNOWING THE TRUE SOLAR RADIATION
1 °) Formula of simple Makkink Formule, but giving a low(weak) evapotranspiration (established for short grass of 2cm of height). A tall grass évapotranspire 10 ‘ furthermore than a short grass according to Bernard.
5 – KNOWING SOLAR RADIATION, WIND SPEED, TEMPERATURE, HUMIDITY OF THE AIR(SIGHT)
Formulates of Penman ( 1 )
It is the best formula but very long to calculate and we do not still possess the necessary elements. She can be applied to periods so short as 5 j bear.
NOTE COMPLEMENTARY(ADDITIONAL)
According to many authors it is false to claim that the potential evapotranspiration is only a function of climatic data: she(it) is also a function of the plant which covers the ground. Certain authors, Blaney-Criddle or Prescott, give coefficients of correction to apply according to the plant or the state of development of the plant.
Really, the potential evapotranspiration is proportional in a coefficient of the roughness of the culture and in a foliaire surface, which facilitates more or less the exchanges of heat with the atmosphere by convection.
The given formulae are valid for a plane surface. It seems that the global energy, thus the evapotranspiration ., for a hillside N or S is boorishly proportional at most of the sine of the angle of beams(shelves)
Conclusion
The future of the delta:
the questions of search(research) and development 40Par many sides, the delta is a land of plenty in the middle of Sahel. By many sides also, he(it) seems fragile and dependent on the fact that the man indeed wants to make it. Because today, the human being has the technical capacity to fit out the site, to modify the movements of the water, the almost magic mechanics of the river. Many of the other sites were so transformed for intensive farming of rice or for electric production.Since the 60s, researchers and technicians put a lot into this region of water, real laboratory for the sciences of the water, the sciences of vegetable and animal life, as well as for the human sciences. Years of search(research) at first by discipline then in a multidisciplinary approach(initiative) which answers the necessity of leading that we call a management integrated(joined) natural resources. The modelling integrated(joined) by the delta and its presentation(display) in the form of IT model (conceived by French IRD-institute of search(research) for the development, in 1999 and 2000) translates a will of synthesis and scientific return(restoration) on behalf of the malian and foreign researchers, but also the consideration of the importance of the search(research) to help decision-makers and users to take the good options of development. Big questions on the future of the delta ask today. These questions are the object for several years of dialogue between public and private, local, national and international bodies.
Is it necessary to fit out him(it), by privileging an extensive but restrictive exploitation(operation) of its resources, some rice in this particular case? Is it necessary to content itself with ecological measures, sites by sites, to rest(support) or restore here and there the natural functionings of this zone of flood? Crucial questioning for the future of the delta. In a more reduced scale(ladder) of time(weather), decision-makers, researchers and developers of the delta are more and more brought to consult to ask the most relevant questions, and try together to answer it. How to observe and to analyze the effective division(sharing) of the resource between the various users? How to manage the low-water mark to assure(insure) the minimum preservation of resource necessary for certain activities? How to regulate the volume of available water?
How to prevent(warn) or to adorn the problems of pollution, quality of water, harmful, of salinisation of the grounds, blocking with sand? Can we prevent(warn) and manage the possible natural disasters and their repercussions on the more and more populated waterside cities? The questions are uncountable and the answers have to take into account multiple and sometimes contradictory interests. But the game(set,play) is worth the candle, because the delta, due to the variety and the complementarity of its resources, can contribute massively to the food autonomy of Mali.
Further reading
- Berry, J.K. (1993) Beyond Mapping: Concepts, Algorithms and Issues in GIS. Fort Collins, CO: GIS World Books.
- Bolstad, P. (2005) GIS Fundamentals: A first text on Geographic Information Systems, Second Edition. White Bear Lake, MN: Eider Press, 543 pp.
- Burrough, P.A. and McDonnell, R.A. (1998) Principles of geographical information systems. Oxford University Press, Oxford, 327 pp.
- Chang, K. (2007) Introduction to Geographic Information System, 4th Edition. McGraw Hill.
- Coulman, Ross (2001–present) Numerous GIS White Papers
- Elangovan,K (2006) »GIS: Fundamentals, Applications and Implementations », New India Publishing Agency, New Delhi »208 pp.
- Harvey, Francis(2008) A Primer of GIS, Fundamental geographic and cartographic concepts. The Guilford Press, 31 pp.
- Heywood, I., Cornelius, S., and Carver, S. (2006) An Introduction to Geographical Information Systems. Prentice Hall. 3rd edition.
- Longley, P.A., Goodchild, M.F., Maguire, D.J. and Rhind, D.W. (2005) Geographic Information Systems and Science. Chichester: Wiley. 2nd edition.
- Maguire, D.J., Goodchild M.F., Rhind D.W. (1997) « Geographic Information Systems: principles, and applications » Longman Scientific and Technical, Harlow.
- Ott, T. and Swiaczny, F. (2001) Time-integrative GIS. Management and analysis of spatio-temporal data, Berlin / Heidelberg / New York: Springer.
- Sajeevan G (2008) Latitude and longitude – A misunderstanding, Current Science: March 2008. Vol 94. No 5. 568 pp. Available online at:
- Sajeevan G (2006) Customise and empower, www.geospatialtoday.com: April 2006. 40 pp.
- Thurston, J., Poiker, T.K. and J. Patrick Moore. (2003) Integrated Geospatial Technologies: A Guide to GPS, GIS, and Data Logging. Hoboken, New Jersey: Wiley.
- Tomlinson, R.F., (2005) Thinking About GIS: Geographic Information System Planning for Managers. ESRI Press. 328 pp.
- Wise, S. (2002) GIS Basics. London: Taylor & Francis.
- Worboys, Michael, and Matt Duckham. (2004) GIS: a computing perspective. Boca Raton: CRC Press.
- Wheatley, David and Gillings, Mark (2002) Spatial Technology and Archaeology. The Archaeological Application of GIS. London, New York, Taylor & Francis.
- La Météo agricole; Jacques Kessler ; Alain Perrier, Christian de Pescara (ISBN 2-908215-00-4)
- Techniques d’étude des facteurs physiques de la biosphère; INRA Publ. 70-4 Dépôt légal 1970 n° d’ordre 9.046. page 425 Méthodes et techniques de détermination des coefficients de transfert et des flux dans l’air.
- Microclimate de Norman J. Rosemberg. (ISBN 0-471-06066-6)
- Limitation to Efficient Water Use in Crop Production. American Society of Agronomy, Inc – Crop Science Society of America, Inc – Soil Science Society of America, Inc (ISBN 0-89118-074-5)
- Turfgrass Management by A.J. Turgeon (ISBN 0-13-933425-4)
- Éléments de Bioclimatologie par H. Chamayou, ingénieur agronome à l’ENSA Montpellier. Collection publiée par l’Agence de Coopération Culturelle et Technique avec la collaboration du Conseil International de la Langue Française. (ISBN 2-85319-237-7)
- Gallais, Jean (1967), Le Delta Intérieur du Niger: étude de géographie régionale (2 Vols.), Dakar: Institut Fondamental d’Afrique Noire (IFAN) .
- Quensière, Jacques, ed. (1994), La pêche dans le delta central du Niger : approche pluridisciplinaire d’un système de production halieutique (2 Vol.), Paris: ORSTOM, Karthala, ISBN 2709912023, http://horizon.documentation.ird.fr/exl-doc/pleins_textes/divers/40722.pdf. Link includes both volumes. Volume 2 includes 8 maps. The L’Institut de recherche pour le développement site also has pdf files containing individual chapters.
- Zwarts, Leo; van Beukering, Pieter; Kone, Bakary et al., eds. (2005), The Niger, a lifeline: Effective water management in the Upper Niger Basin, Veenwouden, the Netherlands: Altenburg & Wymenga, ISBN 90-807150-6-9, http://www.altwym.nl/modules/Bestanden/files/The%20Niger,%20a%20lifeline.pdf. Also published in French with the title « Le Niger: une Artère vitale. Gestion efficace de l’eau dans le bassin du Haut Niger ».
€24.90