Blue Nile Runoff Sensitivity to Climate Change

Abstract

This study describes implementation of hydrological climate change impact assessment tool utilising a combi- nation of statistical spatiotemporal downscaling and an operational hydrological model known as the Nile Forecasting System. A spatial rainfall generator was used to produce high-resolution (daily, 20km) gridded rainfall data required by the distributed hydrological model from monthly GCM outputs. The combined system was used to assess the sensitivity of upper Blue Nile flows at Diem flow gauging station to changes in future rainfall during the June-September rainy sea- son based on output from three GCMs. The assessment also incorporated future evapotranspiration changes over the ba- sin. The climate change scenarios derived in this study were broadly in line with other studies, with the majority of scenar- ios indicating wetter conditions in the future. Translating the impacts into runoff in the basin showed increased future mean flows, although these would be offset to some degree by rising evapotranspiration. Impacts on extreme runoff indi- cated the possibility of more severe floods in future. These are likely to be exacerbated by land-use changes including overgrazing, deforestation, and improper farming practices. Blue Nile basin flood managers therefore need to continue to prepare for the possibility of more frequent floods by adopting a range of measures to minimise loss of life and guard against other flood damage.