Hydrological response of a catchment to climate and land use changes in Tropical Africa: case study South Central Ethiopia

A hydrological modelling at a catchment scale has been used to investigate the impact of climatic and land use change on water resources in data scarce Tropical Africa using a distributed precipitation-runoff modelling system. The model divides a catchment into homogeneous hydrological response units, providing the ability to impose changes in climate or land use spatially. Model parameters were either estimated from different existing data or by calibration against measured discharge data available over 11 years (1985–1995). The model simulation-period was divided into calibration (1986–1990) and validation (1991–1995) periods. The model provided relatively good fits between measured and simulated discharge both at a daily and monthly scales. Based on sensitivity analyses, a 10% decrease in rainfall produced a 30% reduction on the simulated hydrologic response of the catchment, while a 1.5 C increase in air temperature would result in a decrease in the simulated discharge of about 15%. Converting the present day dominantly cultivated/grazing land in the studied river basin by woodland would decrease the discharge at the outlet by about 8%. In order to use the results of this kind of model for decision making and water resources management, the model should be tested under different environment and different scenario conditions. Rainfall measurement and stage-discharge rating curves should be given priority to improve model performance.