Journal des sciences de la Terre et du changement climatique

Abstrait

Trend Analysis for Temperature and Precipitation Extreme Events over the Headwater of Upper Blue Nile, Ethiopia

Tesfay Mekonnen Weldegerima, Belay Simane Birhanu, Tadesse Terefe Zeleke

Increased trends in extreme climate events such as prolonged hot or cold days and intensively rainy days or consecutive dry days have greater negative impacts on society. The present study aims to examine the spatial and temporal characteristics of means and extremes of temperature and precipitation events in the Tana-Beles Subbasin (TBSB) for the 1980-2015 periods. 22 daily extreme climate indices are calculated based on the Expert Team on Sector-specific Climate Indices (ET-SCI) definitions. Monthly, seasonal and annual temperatures show mostly increasing trends. The mean annual maximum and minimum temperatures increased slightly, respectively, by 0.047 and 0.014 oC/yr. The analysis of extreme temperatures also reveals decreasing trends of cold temperature events and a marked increasing trend of warm temperature events. The frequency of cold days/nights has reduced by 33/38 days/nights annually; whereas, the frequency of warm days/nights has increased by 91/83 days/nights. On the other hand, the mean monthly, seasonal and annual precipitations also show mostly increasing trends. The mean annual precipitation show an increase of 5.01 mm/yr which is not significant. Similarly, among the selected precipitation indices the number of very heavy rain days (R20mm), Simple Daily Intensity Index (SDII), very wet days exceeding the 95th percentile (R95p), and annual total wet days precipitation (RCPTOT) shows increasing trend; whereas, only the maximum 1-day precipitation (Rx1day), show an insignificant decreasing trend. Precipitation during the study period shows high variability spatially and temporally. Moreover, the trends of precipitation are inconsistent when compared to the temperature counterparts.