Analysis of Climate Variability and Anthropogenic Impacts on the Water Balance of Lake Chad Drainage Basin

Sustainable utilization of scarce water resources requires a conceptualization and understanding of both local and regional climate variability. This work deals with an analysis of climate variability and human impacts on the water balance of the Lake Chad drainage basin of northern Africa. Mean annual precipitation and discharge time series from 112 rain gauges and monthly mean SST anomalies were used in this study to determine the influence of climate variability on precipitation and river discharge on Lake Chad. Multivariate statistical techniques were utilized to analyze the datasets. Results showed that three EOFs explain spatial-temporal rainfall variability in the basin, accounting for 71% of the total variability in rainfall. The first EOF captures inter-annual rainfall fluctuations. The second EOF explains inter-decadal or long-term variability in precipitation. The third EOF explains rainfall variability to be driven by orographic configuration in the basin.Lake Chad drainage basin can be divided into three sub-regions of homogenous precipitation variability. Sub-region one depicts rainfall variability in the southernmost parts of the drainage basin and spread from west to east. Variability in rainfall at this sub-region is due mainly to the effect of topography on on-coming moisture bearing southwesterly monsoon winds. Sub-region two is mainly concentrated on the lee side of the Mandara and Adamawa mountain chains, the southwestern portions of the Djebel Mara in Sudan and north of Mongo hills in CAR. The inter-tropical convergence zone (ITCZ) brings summer rainfall in this sub-region. The third sub-region defines the northern Sahel - Saharan zone located between 13oN-24oN of the drainage basin. Rainfall variability is mainly a result of the formation of the African Easterly Jet (AEJ) over West Africa in summer due to strong meridional soil moisture gradients. A component of precipitation variability in the basin owes its origin to SST anomalies in the tropical Atlantic Ocean. The first SVD heterogeneous mode has positive correlations in the far northeastern tropical Atlantic while the corresponding co-varying precipitation mode has positive correlations in the mid-southern portions of the Lake Chad catchment and negatively correlates with the rest of the basin. The second SVD mode has positive correlations in the lower northeastern tropical Atlantic while the corresponding precipitation field has positive correlations in the north-western portions of the Lake Chad catchment and negatively correlates with the rest of the basin. By using precipitation as a predictor to discharge in the basin, a very high positive correlation is found with a strong linear relationship between the two fields during the study period. However, a monotonic trend analysis for discharge and precipitation between 1948 and 1988 showed most stations to have experienced significant negative trends and that precipitation decreased by 19% with the 1965-1988 period accounting 76% of the decrease while discharge decreased by 36% with the 1978-1988 period accounting 86.7% of the decrease. This implies climate variability though is responsible for fluctuating Lake Chad water balance, the amplitude of water resources degradation is exacerbated by other causes which could be of anthropogenic origin, accounting 17% (36% - 19%) of the discrepancy. It is recommended that there should be acquisition of high frequency climate data, recording daily evaporation and evapo-transpiration, an assessment of irrigation dams on major inflow rivers, types of irrigation practices, location of dams as well as their operation technologies