Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Aerial photographs further Sahel land change observation

04.09.2008
The Sahel region is vulnerable to drought and desertification which has been advancing increasingly rapidly over the past few decades. Scientists have been using satellite images since the 1970s to measure land-use changes in the region

Deforestation in this region is, however, a factor that dates back much further, to the mid 20th Century. To get round the absence of satellite remote sensing images, a team of IRD researchers and their partners turned to aerial photograph archives 2 used in West Africa since the 1950s for detailed mapping of the region.

The study area covered 500 km2 in south-west Niger and was chosen because its rural environment was representative of a rain-fed mode of agriculture practised by farming communities throughout the Sahel. Four time series of photographs taken in 1950, 1960, 1975 and 1992, gave the opportunity to trace highly accurately changes in such factors as deforestation, soil erosion or pond water level. A fifth time series for the study area, obtained this time by the SPOT satellite, was added to complete the date set. Additionally, field surveys conducted in which farmers were asked to recollect their experience of the changes in the Sahel landscape yielded information for comparison and integration with aerial observation data.

The photographs’ good resolution, down to a few metres, made possible quite clear identification of borders of cultivated plots or of the gullies that cut into the landscape. Image analysis revealed that between 1950 and 1992, 80% of the study area was cleared for expansion of millet cultivation and, to a lesser extent, to provide firewood for local communities Advantage was also taken of these shots to measure the intensity of the deforestation according to the type of terrain. Thus, hillslopes showed as the most strongly affected by clearance (87%), followed by the plateaux (59%) and then the valley bottoms (42%) which remained the best conserved environments.

Removal of the vegetation led to loss of soil rainfall infiltration capacity. This indirect consequence of forest cover could be visualized on aerial photographs which, as the time series progressed, depicted an increasingly extended gully network. The process ended with a landscape resembling an oilcloth. Here, strong runoff means that rainwater rushes down to the valley floors where it accumulates to form ponds which act as temporary retention ponds. They eventually empty thereby charging the groundwater. The aerial photographs gave the possibility to track the progress of this phenomenon. Between 1950 and 1992, the research team thus recorded a 2.5-fold multiplication of the drainage capacities of the regions observed.

This situation was manifest by an increase in dimensions of gullies, which now reached several metres in width, and the appearance of new temporary water points. The link between the decrease in forest cover and an observed water table rise, by an average of 4m between 1963 and 2005, was also clearly established. The aquifer storage capacities rose by 15 % during this period.

Not all the regions of the Sahel are equally vulnerable to deforestation. Yet although the processes have practically reached their maximum in most of the countries that occupy this narrow semiarid band, water erosion has not ceased, the landscape erosion has continued and the soils are still losing fertility.

Some areas of the Sahel, like the south-western part of Niger, are particularly susceptible. These areas should therefore be targeted as a priority in desertification control schemes, differently from other, flatter areas, where the degree of concern stemming from woodland-clearance induced erosion remains lower. In this situation, aerial photographs will help the local bodies responsible to spot more clearly the sectors that require priority protection. Erosion control efforts will gain in effectiveness by making farmers aware of the necessity to conserve the valleys that are still relatively spared from deforestation and concentrating efforts for reforestation and protection of useful woody species, such as the acacia Faidherbia albida, on the plateaux areas and the hillslopes already hit by deforestation.

1. These research studies were conducted jointly with scientists from James Cook University, Cairns, Australia.

2. The aerial photographs were provided by Niger’s Institut Géographique National (IGNN)

Grégory Fléchet | alfa
Further information:
http://www.ird.fr/
http://www.ird.fr/fr/actualites/fiches/2008/fas303.pdf

More articles from Earth Sciences:

nachricht Algorithm provides early warning system for tracking groundwater contamination
14.08.2018 | DOE/Lawrence Berkeley National Laboratory

nachricht Artificial Glaciers in Response to Climate Change?
10.08.2018 | Universität Heidelberg

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: New interactive machine learning tool makes car designs more aerodynamic

Scientists develop first tool to use machine learning methods to compute flow around interactively designable 3D objects. Tool will be presented at this year’s prestigious SIGGRAPH conference.

When engineers or designers want to test the aerodynamic properties of the newly designed shape of a car, airplane, or other object, they would normally model...

Im Focus: Robots as 'pump attendants': TU Graz develops robot-controlled rapid charging system for e-vehicles

Researchers from TU Graz and their industry partners have unveiled a world first: the prototype of a robot-controlled, high-speed combined charging system (CCS) for electric vehicles that enables series charging of cars in various parking positions.

Global demand for electric vehicles is forecast to rise sharply: by 2025, the number of new vehicle registrations is expected to reach 25 million per year....

Im Focus: The “TRiC” to folding actin

Proteins must be folded correctly to fulfill their molecular functions in cells. Molecular assistants called chaperones help proteins exploit their inbuilt folding potential and reach the correct three-dimensional structure. Researchers at the Max Planck Institute of Biochemistry (MPIB) have demonstrated that actin, the most abundant protein in higher developed cells, does not have the inbuilt potential to fold and instead requires special assistance to fold into its active state. The chaperone TRiC uses a previously undescribed mechanism to perform actin folding. The study was recently published in the journal Cell.

Actin is the most abundant protein in highly developed cells and has diverse functions in processes like cell stabilization, cell division and muscle...

Im Focus: Lining up surprising behaviors of superconductor with one of the world's strongest magnets

Scientists have discovered that the electrical resistance of a copper-oxide compound depends on the magnetic field in a very unusual way -- a finding that could help direct the search for materials that can perfectly conduct electricity at room temperatur

What happens when really powerful magnets--capable of producing magnetic fields nearly two million times stronger than Earth's--are applied to materials that...

Im Focus: World record: Fastest 3-D tomographic images at BESSY II

The quality of materials often depends on the manufacturing process. In casting and welding, for example, the rate at which melts solidify and the resulting microstructure of the alloy is important. With metallic foams as well, it depends on exactly how the foaming process takes place. To understand these processes fully requires fast sensing capability. The fastest 3D tomographic images to date have now been achieved at the BESSY II X-ray source operated by the Helmholtz-Zentrum Berlin.

Dr. Francisco Garcia-Moreno and his team have designed a turntable that rotates ultra-stably about its axis at a constant rotational speed. This really depends...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Within reach of the Universe

08.08.2018 | Event News

A journey through the history of microscopy – new exhibition opens at the MDC

27.07.2018 | Event News

2018 Work Research Conference

25.07.2018 | Event News

 
Latest News

'Building up' stretchable electronics to be as multipurpose as your smartphone

14.08.2018 | Information Technology

During HIV infection, antibody can block B cells from fighting pathogens

14.08.2018 | Life Sciences

First study on physical properties of giant cancer cells may inform new treatments

14.08.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>