Hydrological impacts of the changes in simulated rainfall fields on the Nakanbe basin in Burkina Faso

English Abstract:

Changes in rainfall regime during the last five decades over West African Sahel have significantly modified the hydrological regime of many rivers with a significant impact on water resources. In this study, the main hydrological processes on Nakanbe watershed in Burkina Faso are described with two hydrological models: GR2M (lumped and monthly model) and ORCHIDEE (distributed and half hourly model). The two models were calibrated on the watershed from the observed runoff at the outlet of Wayen (an area of about 22 000 km²) over the 1978-1999 period with a Nash-Sutcliffe efficiency criterion of more than 62%. The mean annual hydrological balance on the watershed over 1978-1999 period is composed from both models with 4% of runoff, 10% of groundwater recharge and 86% of actual evapotranspiration. The validated model of ORCHIDEE was then used to assess the hydrological impacts of the changes in the rainfall regime simulated by five regional climate models (CCLM, HadRM3P, RACMO, RCA and REMO) run under the intermediate scenario of A1B. ORCHIDEE simulations show that the hydrological impacts on runoff come mainly from the changes in the rainfall field with regard to the frequency and the intensity of the rain events. The impacts of the decrease in the two characteristics reveal different magnitudes of decrease in water resources. The decrease in the intensity of rainfalls is much more (10% more important) prejudicial to runoff and to groundwater recharge (two times more important) than a decrease in the frequency of rainfalls.