ESTIMATION OF CURRENT AND FUTURE SURFACE WATER AVAILABILITY AND WATER ALLOCATION STRATEGIES FOR DEME RIVER CATCHMENT, OMO-GIBE RIVER BASIN, ETHIOPIA.

Abstract

Despite Ethiopia's abundant surface water resources, increasing water demand and variability in hydrometeorological parameters threaten water availability in many river basins. As there are series of highly competitive traditional irrigators and Livestock water demand issues and shortages over the Deme River catchment, it has been worthwhile to estimate surface water availability and demands under current and future scenarios .This research aims to quantify the current water availability and demands as well as projected components under population growth, agricultural expansion, and climate change future scenarios up to 2060. Data on the catchment's demographic, irrigation, and hydro meteorological parameters have been collected from various sources for the period 1989– 2020. The ensemble mean of two climate model results under RCP 4.5 and RCP 8.5, have been applied to generate future water availability in the catchment for the medium term of the 2050s (2031–2060). The GCM-RCM output has been extracted and bias-corrected against observed climate parameters using the CMhyd tool. The HEC-HMS model has been used to estimate the catchment's water availability, while the Water Evaluation and Planning (WEAP) tool has been applied to model sectorial demands and the allocation of available water among different sectors on a monthly basis. The current year's water availability and demand have been figured to be 132.2 MCM and 55.07 MCM, respectively. Future surface water availability under RCP 4.5 and RCP 8.5 scenarios is decreased to 119.35 MCM and 121.07 MCM, respectively, due to decreased-precipitation and increased-temperature. WEAP modelled demands under two future scenarios: population growth and irrigation expansion, resulting in demand-rise from 72.24 MCM and 72.03 MCM to 92.88 MCM and 92.59 MCM, respectively. Except for irrigation and livestock demand, all other demands were fully met in the baseline period. However, all demands are unmet in future periods and scenarios. The outcome shows that all scenarios and time periods, with the exception of RCP 8.5 under population growth scenarios, experience high water stress conditions in the Dame River catchment. The months with the biggest water stress are January through March, followed by February through December. In the Deme River basin, where the availability of water is threatened by increased water demand and changes in hydro meteorological parameters in both the present and future scenarios, roof water harvesting, resource development, and efficient water usages are imperatives.