Assessment of water supply and demand in Gilgel Gibe watershed, southwest Ethiopia

Integrated water resource management requires reliable information on the available water resources and demand. This study aims to assess the future water supply and demand under the combined effect of climate change and socio-economic scenarios using the HEC-HMS and WEAP model for the Gilgel Gibe watershed. The required spatial, hydro-metrological, and socio-economic data were directly collected from different organizations. The precipitation and temperature data forecasted by regional climate models under representative concentration pathway 4.5 were used to simulate the stream flow using the HEC-HMS model. The unmet demand from 2019 to 2050 was estimated under socio-economic scenarios. The result shows that the reference scenario increased annually by 206 million cubic meters (MCM). Similarly, the unmet demand under the Irrigation Area Expansion (IAE) scenario increased at an annual rate of 90 MCM, the maximum increment rate among all scenarios. However, the annual unmet demand under the New Irrigation Technology (NIT) scenario shows a reduction of 0. 3MCM. The IAE scenario also showed a power production reduction of the Gilgel Gibe hydropower plant I by 12% compared to the reference scenario. However, the power production capacity increased by 15.27% under the NIT scenario. The result indicates that socio-economic scenarios are more responsible than climate change scenarios for the occurrence of water scarcity. Therefore, efficiency maximization-based water resource planning should be implemented to minimize the water scarcity problems. In this regard, the study has valuable information which can aid water resource planners for wise use of decision-making.