IMPACT OF CLIMATE CHANGE ON SURFACE WATER AVAILABILITY AND CROP WATER REQUIREMENT OF WHEAT (Triticumaestivum L) IN KATAR SUB-BASIN, RIFT-VALLEY LAKES BASIN, ETHIOPIA

Abstract

A major effect of climate change is likely to be alterations in hydrologic cycles and changes in water availability. Therefore, this study aims to quantify the impact of climate change on the study area, the likely changes in rainfall and temperatures from the base period by the mid and long term of the century, and the potential implications of those changes on Surface water availability and crop water requirement of wheat in Katar sub-basin, Rift-Valley Lakes Basin, Ethiopia. The Coordinated Regional Climate Downscaling Experiment (CORDEX)-Africa data output of Canadian Earth System Model2 (CanESM2) was selected under representative concentration pathways (RCP 4.5 and RCP 8.5) scenarios for making future climate projections. The projection of future streamflow and crop water requirements of wheat was based on climate scenarios data of the baseline period of 1990-2019. The future projection showed that the maximum temperature will rise by 0.6 0C and 1.2 0C, 1.5 0C and 1.7 0C under RCP4.5 and RCP8.5, and the minimum temperature will rise by 0.8 0C and 1.30C,1.5 0Cand 1.8 0C in the 2050s and 2080s under RCP4.5 and RCP8.5 respectively. According to temperature projections, both future scenarios would see a warmer climate, which could lead to the decrement of rainfall during the Kiremt season by -7.4% and -9.4% under RCP4.5, and -13.8% and -16.6% under RCP8.5 in the 2050s and 2080s respectively. The SWAT (Soil and Water Assessment Tool) model was used to simulate streamflow. The calibrated SWAT model was used for nine years of the baseline period and performed well in the simulation of monthly stream flow. Statistical model performance measure, R2 of 0.79 and ENS of 0.77 for monthly calibration and R2 of 0.78 and ENS of 0.78 for monthly validation respectively, indicated well to very good performance of the model simulation. The climate change parameters used an input to the SWAT model to simulate the future stream flow. The result showed a change in stream flow by 6.2% and 15.2% for RCP4.5, 5.2%, and 13% for RCP8.5 in 2050s and 2080s respectively. Current and future water requirement for the wheat crop was estimated using the CROPWAT model and the output shows that, the total amount of crop water requirement for wheat would be expected to increase by 2% and 5.4 % in 2050 and by 2.8% and 8.1% in 2080 for the RCP 4.5 and RCP 8.5 scenarios, respectively. Therefore, this study may help with the planning and implementation of policies for the development of sustainable water resources and could mitigate the effects of climatic change, especially on locally important crop.