Changes in observed rainfall and temperature extremes in the Upper Blue Nile Basin of Ethiopia

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Ethiopia, a densely populated country with abundant natural resources, is often hit by climate extreme disasters that cause severe damage to life and property every year in one or the other corner. The frequency and intensity of extreme events have increased in the recent decades due to climate change and variability. This study aimed to analyze the changes in observed rainfall and minimum and maximum temperature extremes in the Upper Blue Nile Basin (UBNB) of Ethiopia from 1980 to 2019 periods. The Mann-Kendall (MK) trend test and Theil-Sen's slope estimator were used to estimate annual and seasonal trends. The rainfall and temperature extremes were analyzed using RClimDex, which is a graphical user interface in R software, by selecting ten rainfall and eleven temperature indices. The results showed a positive trend in annual, dry (March–May) and small rain (October–February) seasons rainfall in more than 54% of the stations and a decreasing trend in the main rain (June–September) season rainfall in 65.4% of the stations. Several extreme rainfall indices showed insignificant positive trends in the basin. Although there is a positive trend in extreme rainfall, the number of consecutive wet days (CWD) and the simple daily intensity index (SDII) show insignificant negative trends in most stations. In addition, a warming trend of the annual and seasonal maximum and minimum temperature extreme indices was noted. Overall, the increase in extreme rainfall and a warming trend in the extreme temperature indices indicate signs of climate change in the UBNB. The findings of this study suggests the need for developing climate change adaptation and mitigation strategies in the UBNB.

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