Abstract:
The impact of the climate change such as an increase in the temperature, and rainfall seasonal
shift are observable in the world and particularly in Ethiopia. These changes may affect the socio
economic life of the people if it is not assessed and predicted well. Regional Climate Models
(RCMs) are mostly used in local scale assessment of climate change. But due to reflection of the
inherent and methodological uncertainties in climate modeling, the reliability of individual models
needs to be assessed before using their output for impact and climate change assessment. The
objective of this study is to evaluate the performance of RCMs under the project of Coordinated
Regional Climate Down-Scaling Experiment (CORDEX) African domain under Representative
Concentration Pathways (RCP) of 4.5 and 8.5 scenarios. The RACMO22T, CCLM4, RCA4 and,
HIRHAM5 models which were driven by ICHEC-EC-EARTH are evaluated against observed
rainfall and air temperature data for a period of (1986 to 2005) over the Wabi Shebele basin,
Ethiopia. The statistical measures like Bias, RMSE and, r were used for model performance
evaluation. The evaluation is mainly on how best RCMs performed in simulating annual rainfall,
maximum, and minimum air temperature over the study area. All models best simulated in dry
months. In air temperature simulations, all models under simulated the maximum temperature and
overestimated the minimum temperature in most months. Based on statistical result for
performance evaluation, monthly cycle, annual and seasonal variability of the RCMs, RCA4 was
well performed in both simulating rainfall and air temperature. After the models performance was
checked, the best performed model, RCA4 was selected and bias corrected. With the use of Rstudio
software wich is high programming language trend was analysised for time series of annual
rainfall, maximum and minimum air temperature for observed (1986-2005). Further,the best
performed model bias corrected data under both RCP scenarios for a period of 2031-2050 and
2051-2070 years was done. The results of trend analysis indicated that a decrease in annual
rainfall and an increasing trend in average maximum and minimum air temperature for selected
scenarios over the Wabi Shebele basin. In this regard, RCA4 regional climate models have to be
used for any climate change impact study and for local-scale climate projections over the Wabi
Shebele basin
