CLIMATE CHANGE IMPACT ON DROUGHT CONDITIONS, KESEM SUB BASIN, AWASH RIVER BASIN, ETHIOPIA

Abstract

Nowadays the Intergovernmental Panel on Climate Change concluded that climate change is happening with multifaceted effects on humans and the environment thus, this study strives to examine the likely impacts of climate change on drought conditions at Kesem sub basin of Awash River Basin, Ethiopia. The analysis was undertaken using drought indices and estima-tion of dry spell occurrences with aid of Markov chain probability model. The Hydrological and meteorological data were used as an input for the analysis. In addition to the base period (1984-2014), future scenarios (2015-2044) and (2045-2075) projection were made based on the output of ensemble of 17 GCMs with aid of a MarkSim-GCM for two emission scenarios, the medium (RCP4.5) and the high (RCP8.5). In the area based on observed data, average monthly maximum temperature fluctuates in the range of 19.4 to 36.3oC and the average monthly minimum temperature was in the range of 2.7 to 20.4oC. Concerning the temperature change, there is an increment of Tmax of +1.8ºC from base period to RCP 4.5(2020) and +3.2ºC to RCP4.5 (2050), +2.3ºC to RCP 8.5(2020) and +3.3ºC to RCP8.5 (2050). Likely, there is a rise of Tmin of +3.9ºC from base period to RCP 4.5(2020) and +4.3ºC to RCP 8.5(2020), and +5.5ºC to RCP4.5 (2050) and +6ºC to RCP8.5 (2050). Concerning the rainfall change, there is increment of +345.5mm (33.1%) from base period to RCP 4.5(2020) and +95.5mm (12%) to RCP 8.5(2020) and +443.6mm (38.8%) to RCP4.5 (2050) and +93.1mm (11.8%) to RCP 8.5(2050) scenarios. Likely, the PET loss shows increment of +25.9mm (1.6%) from base period to RCP 4.5 (2020) and +26.7mm (1.7%) to RCP 8.5 (2020), and +55mm (3.4%) to RCP4.5 (2050) and +56.8mm (3.5%) to RCP8.5 (2050). The study revealed that, the mean onset and offset of Belg is during 72 and 126 DOY and for Kiremt during 169 and 290 DOY respectively. During Belg season the probability occurrence of dry decade was more than 81% for the decades 4th to 8th and 13th to 15thand probability occurrences of dry decades preceded by dry decades were more than 80% for all decades. In Kiremt season the probability of having a dry decade of more than 50% was during 16th to 18th, and 25th to 27th decades and probability occurrences of dry decades preceded by dry decades were observed to be more than 50% for decades 16 th to 18 th and 23 th to 27 th. Considering the long term drought conditions, in the base period, 49.5% meteorological, 70.9% agricultural, 63.3% hy-drological drought were observed. In the RCP 4.5 (2020) 57.5% meteorological, 43.3% agri-cultural, 80% hydrological and in the RCP 4.5(2050) 41.4% meteorological, 66.7% agricul-tural, 23.3% hydrological drought will be expected. In the RCP 8.5 (2020), 42.8% meteoro-logical, 40% agricultural, 53.3% hydrological and in the RCP 8.5(2050), 49.7% meteorologi-cal, 46.7% agricultural, 60% hydrological drought will be expected. The study found that due to combined effects of projected change in rainfall and temperature there will be increment of PET and then drought so that, future studies must recognize the overall implication of climate change in the sub basin.