Biomass Burning and Its Relationship with Water Cycle Dynamics of the Chari-Logone Catchment of Lake Chad Basin

Abstract

The present study investigates the effect of biomass burning on the water cycle dynamics of the Chari-Logone catchment, which is the primary water source of Lake Chad, in central sub-Saharn Africa, providing approximately 95% of surface water inflow to the lake. A significant challenge in calculating water balance for this region is the lack of meteorological station data and the low temporal frequency of sampling by the few existing stations. WetSpass-M, a monthly water balance model, was chosen for this study due to its ability to calculate water balance without the large amount of data that many other models require. Satellite observations from TRMM, MODIS, and SRTM, and other earth science missions provide well distributed data at reasonable spatial scales. For a more comprehensive look at the effects of burning, i.e. albedo change, which has been shown to have a significant impact on a number of environmental factors, was considered when calculating potential evapotranspiration as a model input. Two water balance simulations, one considering burning and one without, were compared from the years 2003 to 2011. A groundwater model was also built using Processing MODFLOW, using actual evapotranspiration from both burning and non-burning water balance outputs. The resulting calculated runoff from the model agreed well with ground observations, with a Nashe-Sutcliffe Efficiency of 0.57. Seasonal analysis shows a correlation between water-cycle parameters and burning, and is affected by the region's seasonal variability, where burning increases during the dry season and decreases during the wet season. The groundwater model performed well for dry season months when there was less rainfall. However, when wet season evapotranspiration (ET) was used, the model over exaggerated the groundwater levels. This was most likely due to the way the groundwater and evapotranspiration parameters are handled in WetSpass-M. When the primary land cover types were studied (grass, savanna, and cropland); all three land cover types showed a significant reduction in ET. This is shown by average wet season ET decreasing -5.E+13 m³per month and a decrease 7.E+13 m³for the dry season months. This lends support to the hypothesis that with increased burning, there is a decrease in certain hydrologic parameters including precipitation.