Trends in Extreme Climate Events over Three Agroecological Zones of Southern Ethiopia

Abstract

The study aims to assess trends in extremes of surface temperature and precipitation through the application of the World Meteorological Organization’s (WMO) Expert Team on Climate Change Detection and Indices (ETCCDI) on datasets representing three agroecological zones in Southern Ethiopia. The indices are applied to daily temperature and precipitation data. Nonparametric Sen’s slope estimator and Mann–Kendall’s trend tests are used to detect the magnitude and statistical significance of changes in extreme climate, respectively. All agroecological zones (AEZs) have experienced both positive and negative trends of change in temperature extremes. Over three decades, warmest days, warmest nights, and coldest nights have shown significantly increasing trends except in the midland AEZ where warmest days decreased by 0.017°C/year ( $p<0.05$). Temperature extreme’s magnitude of change is higher in the highland AEZ and lower in the midland AEZ. The trend in the daily temperature range shows statistically significant decrease across AEZs ( $p<0.05$). A decreasing trend in the cold spell duration indicator was observed in all AEZs , and the magnitude of change is 0.667 days/year in lowland ( $p<0.001$), 2.259 days/year in midland, and 1 day/year in highland ( $p<0.05$). On the contrary, the number of very wet days revealed a positive trend both in the midland and highland AEZs ( $p<0.05$). Overall, it is observed that warm extremes are increasing while cold extremes are decreasing, suggesting considerable changes in the AEZs.