Synergistic remote sensing of Lake Chad: Variability of basin inundation

During recent decades, drought and anthropogenic influences have led to the diminishment of Lake Chad with adverse effects on both food and water resources. The local population has learned to adapt to the reduced seasonal inundation of the lake basin but are vulnerable to both droughts and excessive inflows. Here synergistic satellite radar altimetry and near-infrared imagery are employed to gain knowledge of the current flooding patterns. Variations in surface level for the inflowing rivers and the permanent and seasonal lake waters are derived for the 1990s using data from the TOPEX/POSEIDON satellite. National Oceanic and Atmospheric Administration's Advanced Very High Resolution Radiometer images provide additional variations of basin inundation from 1995 to 1998, using a simple pixel histogram technique. With accuracy greater than or equal to 10cm rms, the altimetry reveals seasonal water-level variations of the order 0.5-6 m and there is a notable rise in minimum levels, 15-35 cm year(-1) within the lake basin. Peak-level phase lags of 4 to 5 months are also observed between the headwaters of the Chari/Logone rivers and the western lake marshes. Image results reveal that the permanent lake area is similar to 1.385 km(2), and that with an accuracy of similar to 5% the surrounding regions have been additionally flooding by up to similar to 3,600 km(2) year (-1). Despite current basin complexities, the synergistic area/level measurements corroborate the know hydraulic relationship at low water levels. Both measurement sets reflect the poor inundation years of 1993/1994 and 1997/1998, despite the indication of a general recovery in regional precipitation, inundation extent, and surface water level offers these remote sensing techniques as an additional tool for flood/drought forecasting and the availability of future fast delivery data, a mechanism for near-real time monitoring. (C) Elsevier Science Inc., 2000.