Climate change in the Blue Nile Basin Ethiopia: implications for water resources and sediment transport

As much as 66% of the Nile River flow that reaches Egypt originates in the Highlands of the Ethiopian Blue Nile Basin (BNB). This imbalance in water availability poses a threat to water security in the region and could be impacted by climate change. This study coupled a watershed model analysis with bias corrected and downscaled Intergovernmental Panel on Climate Change (IPCC) Coupled Model Intercomparison Project 5 (CMIP5) climate data to assess the potential impact of climate change on water resources and sediment dynamics in two critical headwater basins of the BNB. Climate scenarios analyzed include RCP2.6, RCP4.5, RCP6.0, and RCP8.5 from six climate models, which were used to force watershed models calibrated against historic streamflow for six gauged sub-watersheds in the Tana basin and four gauged sub-watersheds in the Beles basin. We developed distributed watershed model parameter estimates from the gauged sub-watersheds, which were applied to un-gauged portions of the basins using topographically informed parameter transfer functions. We analyzed the impact of climate change for two future time periods (2041-2065 and 2075-2099) by running each of the six downscaled and bias corrected CMIP5 model predicted climate forcings through the watershed models to assess the impact of ensemble model mean and variance in climate change prediction on water availability and sediment transport. Results indicate that the Tana and Beles basins will experience increases both in mean annual flow (22-27%) and sediment concentrations (16-19%). Interestingly, and of significance for water availability and hydropower development, the monsoon in the Tana and Beles basins will lengthen by approximately four (Tana) to six (Beles) weeks. These results highlight both the considerable variance in climate change impacts as well as the potential for beneficial outcomes in the region.