Study of Water Allocation for Existing and Future Demands under Changing Climate Condition: Case of Upper Awash Sub River Basin

Abstract

The main aim of this study is to study the existing and future water availability under climate change in upper awash sub-basin which contributes significant flow to Koka dam and also on water allocation of the existing and planned water resource projects (irrigation, hydropower, industries, livestock etc.) in the upper awash. HEC-HMS hydrologic model is used to assess the water availability of sub-basin. The future stream flow forecasted in the sub-basin were simulated by the dynamically downscaled A1B scenarios known as RCP 4.5 (Representative Concentration Pathways) has been adopted from CORDEX archive and bias correction were done by using power transformation equation before using in HEC-HMS model. The result of future water availability from 2006 to 2031 in sub-basin was found to be nearly 1001 MMC. The Water Evaluation and Planning System (WEAP) model is used for optimal water allocation for existing and proposed water resource projects using the monthly based data in both the demand side and supply sides and by priority setting situation for demand sites. The reference period used for the simulation ranges from 1981-2009 while the future scenario period ranges from 2006-2031.The monthly water requirement for each crop mainly sugarcane is estimated using Cropwat 8.0 software by adopting Penman Monteith approach and crop coefficient of the crop. The existing irrigation projects were around 95,155 ha while in the future scenario period the irrigable land expected to increase by 21,103 ha. According to reference scenario the downstream irrigation project shows the highest supplied volume about 479.4 MCM annually. According to future scenario period the UV1 and UV3 irrigation projects shows increasing water demand from the refinance period by about 203.5 and 357.5 MCM annually due to expansion of the irrigation projects. The annual water demand and supplied for the reference period found to be 1716.3 MCM while the demand increases to 1953.3 MCM for the future scenario with no unmet demand.

Keywords: Upper Awash, Climate Change, RCP, HEC-HMS; WEAP, Koka Dam, Scenario development, Water requirement.