ASSESSMENT OF METEOROLOGICAL DROUGHT BY USING THE SPI INDEX: A CASE STUDY IN CENTRAL RIFT VALLEY OF ETHIOPIA

Abstract

Drought is a complex and recurring phenomenon that has impacts on agriculture, water supply, and ecosystems. Even if its characteristics vary significantly from one region to another, and differs from aridity that is a permanent feature of climate restricted to low rainfall areas drought occurs in all climatic zones. Therefore, it is very important to increase the understandings of the concerned body and local community in the continent in general and in Ethiopia in particular for future most likely drought impacts. The objective of this study was to identify the past and projected meteorological drought by using the standardized precipitation index, in case of Central Rift Valley of Ethiopia. For this study 34 years historical precipitation data from (1985-2019) and (2020-2100) years projected climate data were used for analysis. RStudio software was used to calculate SPI at the nine major station to identify historical and future meteorological drought. The Mann-Kendall trend test and Sen’s slope estimate were employed to find the nature of the drought, rainfall and temperature trend and significance level in the study area. Results showed that the study area was under drought condition in (1991-1992), (2015-2016), (2017-2018) and 2019 in historical period and for projected period in near future (2022, 2029 and 2046) in mid future (2058, 2065 and 2061,2068) in far future (2099, 2085 and 2099,2083) which were among the drought years for both RCP4.5 and RCP8.5 respectively. For historical data SPI-3 showed that 325 moderate, 141 severe and 87 extreme droughts events. Again, 3-month standardized precipitation index showed that 392 moderate, 171 severe and 95 extreme droughts events for RCP4.5 and 456 moderate, 142 severe and 80 extreme number of drought events occurred for RCP8.5. Statistical analysis for historical data showed increasing trends of drought at three-month timescale in Langano and Ziway station but decreasing tendencies in Tora, Kulmsa, Koshe, Degaga and Arsi Negele stations at significant level of (p < 0.05). RCP 8.5 shows significantly decreasing trend with the S-test of -158 and with the Z-value is |Z|> 1.96 at near future, (S-test= -122, Z=-2.3) at far future for 95% confidence level. But RCP4.5 shows decreasing trend at mid future (S-test=-106, Z= -1.67). Finally, from the result we conclude historical drought and projections indicated that its intensity, severity and duration is increase under past data as well as for both analyzed RCPs (RCP4.5 and RCP8.5).