Testing CORDEX GCMs for Projecting Rainfall in Amhara, Ethiopia

Abstract

Five CORDEX Global Circulation Models (GCMs): ICHEC-EC-EARTH, MIROC5, HadGEM2-ES, MPI-ESM-LR, and NorESM1-M were tested and validated for projecting rainfall in the Amhara regional state of Ethiopia. The GCMs were evaluated in terms of their performance during the historical period 1981-2020 and of the near-term, mid-term, and long-term future periods in three Representative Concentration Pathway (RCP) scenarios, RCP2.6, RCP4.5, and RCP8.5, across 71 grid points. Monthly observed rainfall data was used to compare the GCMs' performance and correct their biases using three non-parametric quartile mapping methods: robust empirical quartiles, empirical quartiles, and smoothing splines. The results show that HadGEM2-ES and MPI-ESM-LR had the best performance in the study area. The test and validation results for these two GCMs have come up with r = 0.8, NSE = 0.5-0.6, and RMSE = 64-70 mm/month. As there was a large discrepancy in historical and projected CORDEX rainfall data, bias correction was necessary, and the robust empirical quartiles method was found the best for the Amhara region. Compared to the historical, there will be a decrease in the monthly rainfall amount for the months of March, May, June, July, and October and an increase for the rest in all projected scenarios. The result concluded that using an ensemble of HadGEM2-ES & MPI-ESM-LR GCMs would better simulate the rainfall in the Amhara region