GROUNDWATER RECHARGE RESPONSE TO CLIMATE CHANGE IN A YNALEM-CHELEKOT WATERSHED, TEKEZE BASIN

Abstract

roundwater systems in arid regions are particularly sensitive to climate change owing to the strong dependence of rates of evapotranspiration on temperature, and shifts in the precipitation regime. The physically based WetSpass model coupled to MODFLOW model is used to assess groundwater recharge response to climate change in Aynalem-Chelekot watershed, Tekeze basin. Climate change scenarios from HadCM3 model with A2a and B2a SRES emission scenarios for the future times of 2020s (2011-2040), 2050s (2041-2070) and 2080s (2071-2099) were downscaled to local conditions using SDSM model. The Projected climate change scenarios show an increasing trend for both maximum and minimum temperatures. However, annual precipitation show decreasing trend in 2020s then increase in the remaining future periods. The current spatially distributed annual recharge rate is estimated as 51 . 7mm/year with higher recharge rate during the rainy summer season. The average annual spatial recharge rate to the watershed is projected to decrease by 5.47% for A2a scenario and by 4 . 56 % for B2a scenario in 2020s and annual increase for both A2a and B2a emission scenarios during 2050s and 2080s. Groundwater recharge rate during summer season is expected to decrease in 2020s and increase in 2050s and 2080s for both scenarios . However, during winter season it is expected to decrease in 2020s and 2050s for A2a scenario and increase in all future periods for B2a scenario. Even though projected temperature is expected to increase by considerable amount resulting in increased evapotranspiration, increase in precipitation outweighs the effects of temperature on groundwater recharge rate. The seasonal changes in future groundwater recharge are strongl y pronounced during summer season than winter season responding directly to higher changes in precipitation during the rainy summer season. The predicted decrease in future groundwater recharge might fail to meet water demands of the community within and around the watershed. Adopting water storage structures to store the excess water flowing during summer season and employ other adaptation options is recommended.