Water !

Africa boasts several of the world's largest wetlands. Some of these wetlands are located in the Sahel, an otherwise dry and hot area where rainfall is scarce and unpredictable. These flood plains are fed by rivers (Chari, Logone, Niger, etc.) carrying water from the wet South. It takes several months before the surface water flows off and is carried away via the rivers. This means that the maximum water level in the flood plains is only attained in October. By that time, the dry season has already been under way for several months. The plain dries out very gradually, and until the end of February there is still enough soil moisture in places to support lush green vegetation. Both for herdsmen and their animals and for wild animals (elephants, gazelles, antelopes, giraffes, etc.), the flood plain is indispensable to get through the long dry season.

Yet there is a problem: over the past 40 years, the human population in the area has grown substantially, and the demand for agricultural land and irrigation water is increasing. Therefore dams are being built and irrigation networks laid out.

However, these completely disrupt the natural hydrology of the wetlands. At places the plain is completely dried out, with the predictable consequences for livestock and wild animals. Various organisations, such as the WWF (World Wildlife Fund) and the IUCN (International Union for the Conservation of Nature), are trying to combat this. Using refined hydrological models, the effect of each intervention (such as digging canals, cutting dikes, etc.) is forecast. The final result is evaluated with the aid of field observations and satellite images (SPOT-XS, LANDSAT-MSS, radar, etc.). Given that these wetlands are very extensive and dynamic, they can also be studied using images with low spatial and high temporal resolution, such as NOAA-AVHRR and SPOT VEGETATION. With the aid of these images, vegetation maps can be made and change processes (dehydration, etc.) can be monitored.