Hydrological response of a catchment to climate change, case study on Upper Beles Sub-Basin, Upper Blue Nile, Ethiopia

Global warming will likely alter the hydrological cycle in a ways that have substantial impacts on water resource availability. Changes in temperature, precipitation amount, patterns and intensities and evapotranspiration will almost directly affect the water balance of the drainage basin and stream flow in rivers. Such changes in the hydrological cycle component will have significant impact on the local and regional hydrological regimes which in turn affects ecological, social and economical systems.Although quantitative estimates of hydrologic effects of climate change are essential for understanding and solving the potential water resource management problems associated with power generation, agriculture and water resource planning and management, the current coarse resolution of general circulation models (GCMs) does not provide reliable estimates of meteorological variables at the appropriate scale required for regional impact assessments.Hence more reliable meteorological variables such as temperature and rainfall corresponding to future climate scenarios can be derived from GCMs outputs using the so called 'downscaling techniques'. In this study Statistical downscaling model (SDSM) and Temporal Neural network were used to downscale the GCM model outputs in particular precipitation and temperature to generate the possible future scenarios in the Upper Beles Sub-Basin, Upper Blue Nile, Ethiopia. The downscaled meteorological variables were subsequently used as input to the HEC-HMS hydrological model to simulate the corresponding stream flow change.Results of the impact assessment over the basin showed projected increase in annual runoff ranged from18 % in 2050s to 11% in 2090s for A2a emission scenario. The Sensitivity analysis based on incremental scenarios showed that a drier and warmer climate change results in reduced runoff. A 20 % decrease in rainfall coupled with a 2 oc increase in temperature would result in a 41 % decrease in annual runoff