Evaluation of Climate Change Impacts on Irrigation Water Requirement (A Case Study of Metehara Sugar Estate, Ethiopia)

Abstract

Climate change is the main source of fluctuation in global food production, particularly in the tropical countries of the developing world. Water resources are under pressure, with an increasing deficit between available supplies and water demand and climate change is further exacerbating the water scarcity through rising temperatures which likely increase the quantity of evaporation combined with unevenly distribution of rainfall are adversely affecting irrigation water availability in the Metehara Sugarcane Estate. In this study, therefore, climate change which triggers changes in temperature and precipitation and its effect on current and future sugarcane irrigation water requirement have been studied considering Metehara Sugar Estate in Ethiopia as a case study. The climate change impacts on temperature and precipitation characteristics within the watershed have been studied using CanESM2 climate model for RCP8.5, RCP4.5, and RCP2.6 scenarios from coupled model inter-comparison project 5 (CMIP5) experiments which have been downscaled by statistical downscaling model (SDSM). Long term climate change and its effects on sugarcane irrigation water requirement for current and future time period under three RCP scenarios with three thirty year time slices (2020s, 2050s, and 2080s) were estimated by FAO CROPWAT software program. The change in mean annual maximum temperature from the base period has indicated increment by 0.32, 0.33, and 0.2 °C in the RCP2.6,0.33 ,0.41, and 0.44 °C in the RCP4.5, and 0.37,0.42, and 0.5°C in the RCP8.5 for the 2020s, 2050s, and 2080s, respectively while in case of mean annual minimum temperature an increment by 0.05,0.025, and 0.074°C in the RCP2.6, 0.064, 0.067, and 0.09°C in the RCP4.5, and 0.1,0.12 and 0.2 °C in the RCP8.5 for the 2020s, 2050s and 2080s, respectively. In case of precipitation, increment of mean annual percentage change from the base period was detected by 1, 4.4, and 2.97% in the RCP2.6, 3, 4.94, and 6.74 in the RCP4.5, and 3.1, 5.05, and 8.7% in the RCP8.5 for the 2020s, 2050s, and 2080s, respectively. The result of annual future sugarcane irrigation water requirement showed an increase by 5.15 mm (0.8%) and 1.9 mm (0.3%) in 2020s and 2080s respectively; however it decreased by 9 mm (1.36%) in 2050s under RCP2.6. The future sugarcane irrigation water requirement was increased by 1.73mm (0.26%) in the 2020s while it was decreased by 2.78 mm (0.4%) and 7.8 mm (1.2%) in the 2050s and 2080s respectively under RCP4.5. Under RCP8.5, the future sugarcane irrigation water requirement was increased by 0.6 mm (0.08%) and 5.2 mm (0.78%) in 2020s and 2050s respectively; however in the 2080s, it showed decline by 3.33 mm (0.5%) in relative to baseline scenario. It’s clearly observed from the results that there is considerable temporal variations of sugarcane irrigation water requirement under three RCP scenarios in all the future time periods which implied that climate change is putting significant impact on irrigation water requirement