Monitoring climate extremes using standardized evapotranspiration index and future projection of rainfall and temperature in the wettest parts of southwest Ethiopia

Abstract

Ethiopia is categorized as one of the most vulnerable countries to climate extremes. A better understanding of climate extremes at short and long timescales is therefore crucial to minimize the potential impacts of these extremes. The present study aimed to characterize the frequency and severity of agricultural and hydrological drought in southwestern parts of Ethiopia over the period 1971 to 2020. Satellite blended/gridded and historical observed monthly rainfall, maximum temperature and minimum temperature data of nine stations (Arjo, Bako Tibe, Bedele, Didessa Dildey, Gedo, Gimbi, Sekoru, Serbo and Nekemte) were obtained from Ethiopia National Meteorological Agency. We used standardized evapotranspiration index (SPEI) to calculate the dry and wet condition at 3-, 6-, and 12-months timescales. Besides, past climate change analysis, future rainfall and temperature were projected under four representative concentration pathways (RCPs) of CMIP5 for the near and mid-term (2041-2060) and end of the twenty-first century (2081-2100). Our results showed that the frequency of drought in the short timescales is much higher than that of the longer timescales. In the present study, a total of 108 and 111 drought months were observed at Bedele and Nekemte, respectively at SPEI 3 and both stations recorded a total of 101 at SPEI 6. An increase in projected mean minimum and maximum temperature by 1.2°C was observed by the end of 21st century comparative to the reference time (1986-2005) under a high emission scenario (RCP8.5). Projected changes in rainfall showed a slight increase over the periods 2041-2060 and 2081-2100 under RCP4.5, RCP6.0 and RCP8.5, while projected trends under RCP2.6 indicated a slight decrease. The results of this study will be useful to design effective climate resilience agriculture in the study area. Moreover, it provides evidences for policy makers towards climate change adaptation and mitigation in the southwestern parts of the country.