Observed and Future Climate Variability, Trend and Extremes in Central Highlands of Ethiopia: A Case Study at Arsi Robe, Asasa, Debre Zeit and Kulumsa Areas

摘要

The study was conducted with the aim to analyze the variability of onset, cessation and length of growing season, and trends of daily values of temperature and precipitation extremes. The future climate data are downscaled using Marksim weather generator from the outputs of seventeen climate models (GCMs) for 2050s under RCP4.5 and RCP8.5 scenarios. The onset of the rainy season was highly variable than its cessation in the study area during the base period (1981-2015). In this regard, Asasa has experienced high variability of the onset date (CV=37%) followed by Kulumsa (CV=32.6%) and Debre Zeit (CV=32.4%) areas. The mean end of season in the study area was on 256, 298, 272 and 257 DOY at Asasa, Arsi Robe, Debre Zeit and Kulumsa sites, respectively. Analysis of 27 core set of extreme climate indices, which has been developed by ETCCDI is carried out for baseline and future periods, and the results of eighteen of them is discussed in detail in this work. The increase in lowest minimum temperature (TNn) is greater than that in highest maximum temperature (TXx) which represents the coldest or hottest days in a year, season or month respectively. The annual number of days with daily temperature greater than 25ºC referred to as summer days (SU25) will be increased highly while the frost days, when minimum temperature is less than 0ºC will be decreased in all study sites under both RCPs. Overall, the extreme temperature indices showed that, warm extremes are increasing while cold extremes decreasing in all study sites during mid-century, this series clearly indicate significant warming. From the precipitation extremes, the number of consecutive dry days (CDD) showed decreasing trend under RCP4.5 and increasing under RCP8.5 at Asasa and the reverse trend of this index is observed in Kulumsa area.