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    ASSESSMENT OF METEOROLOGICAL DROUGHT BY USING THE SPI INDEX: A CASE STUDY IN CENTRAL RIFT VALLEY OF ETHIOPIA
    (Hawassa University, 2022-04-28) BEREKET DESELEGN ASHEBO
    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).
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    METEOROLOGICAL DROUGHT ANALYSIS: THE CASE OF ABAYA- CHAMO SUB-BASIN
    (Hawassa University, 2019-03-22) TESHOME AFIRA DULECHA
    Meteorological drought is the deficit in precipitation over a region for a period of time which in turn results in the reduction of moisture condition of the soil and then the crop yield. It has severe socio-economic and environmental impacts which require to careful monitoring of drought conditions using a suitable index. The objective of this research was to analyze meteorological drought frequency, severity and duration in the Abaya-Chamo Sub-basin using the application of SPI for monthly rainfall records. After checking the data quality and fitting the Gamma statistical distribution for each selected station as a requirement of the SPI, the analysis was done for the past 30 years of record from 1988 to 2017 for five selected stations based on monthly precipitation records using the index at 1-, 3-, 6-, 9- and 12-month timescales. The results show that, no correlation exists between successive observations, and thus, the data are independent, and there was no persistence in the time series. The inter-site correlation was less than one (R2<1) for all the statios and hence all the stations in the sub basin were consistent. For both convectional Cv and L-Cv based homogeneity tests the coefficient of correlation (CC) values were less than 0.3 showing the homogeneity of the stations. Gamma probability distribution was determined as the best fit statistical distribution for the data set since the typical alpha level was greater than 0.05 at 95% of confidence interval as checked using Kolmogorov Smirnov and Shapiro Wilk’s test using SPSS. All of the studied meteorological stations experienced drought episodes in 1988, 1989/1990, 1992/1993, 1999,2000/2001, 2003/2004 and 2007/2008 which were among the worst drought years in the history of Ethiopia, and moderate drought events ranging from the SPI values of -1.49 to -1 were pronounced with greater frequency than other dry events. Severely dry events were occurred at values between -1.99 and -1.50. The maximum SPI value of extreme dry event was -2.69. The year 1999 was the most drastic and distinct-wide extreme drought episode in all studied stations. The findings of this study have implications for drought management, early warning system, preparedness and contingency planning and climate change adaptation
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    ANALYSIS AND PRIDICTION OF METEOROLOGICAL DROUGHT USING STANDARDIZED PRECIPITATION INDEX: CASE STUDY OF EASTERN OROMIA
    (Hawassa University, 2019-02-14)
    Ethiopia is one of the most drought affected country in Africa and suffered from acute drought many time in recent years. The objective of this study is to understand the rainfall variation and conduct an in-depth analysis and prediction of drought for to Eastern Oromia. Standardized precipitation index (SPI) was selected to characterize drought condition in the region. Drought characteristics at a time scale of 2-month, 3-month, 6month and 12-month were computed separately for 22 selected rain gauge station. The most maximum drought characteristics at 2-month, 3-month, 6-month and 12-month time scales have been found in Hararegie over last 36 years (1979-2015). The spacial extent of drought and rainfall variation were determined from SPI and CV values computed separately for each rainfall have been interpolated between station in Arc view GIS environment. The rainfall variation shows that the rainfall over the study area is highly variable and increases from Arsi to East Harargie and in the recent last decade (2005-2015) the map of SIP-3 (Belg) shows that a spacial extent drought over study area was irregular and there were no period in recent decades (2005-2015) without drought at least mild drought and this shows that the area is vulnerable to drought. The maximum intensity of (5.33) was recorded at Fedis Station for SPI-3 (kiremt season) in a year 1996, maximum intensity of (4.04) was recorded at Kobo Station in a year 1985 for SPI-3 (Belg season), maximum intensity of (4.77 and 4.5) were recorded at Ticho Station for SPI-6 (both seasons) and SPI-12 (annual) respectively. The drought prediction was made until 2043, using the Representative Concentration Path way (RCP) 8.5 Scenario.on the basis of the drought index measured by SPI. From the analysis of the drought index through the RCP 8.5 Scenario, extreme drought intensity will be more likely to occur. The long-term forecast (12-month period unit) showed that extreme drought would occur severely at station Diksis Sude, Hirna and Adelle from 2035 to 2040 and need more attention for this area
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    ANALYSIS AND CHARACTERIZATION OF HYDROLOGICAL DROUGHT UNDER CLIMATE CHANGE IN HAMASSA WATERSHED, RIFT VALLEY BASIN
    (Hawassa University, 2024-07-20) REDIAT LEGESE SIME
    Hydrological drought occurs when there is an extended period of significantly reduced water availability, leading to depleted water sources and severe impacts on ecosystem and communities. Water scarcity caused by prolonged periods of reduced rainfall due to climate change can lead to the natural disaster of drought. However, little has been done so far on hydrological drought under climate change in Hamassa watershed. This study aimed to analyze and characterize hydrological drought under climate change in the Hamassa watershed, Rift Valley Basin, Ethiopia. Hydrological data (1992-2015), meteorological data (1992-2022), future climate data 2030-2090), spatial data, DEM, land use land cover, and soil were collected. CMhyd software package was used for bias correction of the climate data. The hydrological model soil and water assessment tool (SWAT) was used for hydrological analysis. The simulation result was calibrated and validated using the SWAT calibration uncertainty procedure (SWAT-CUP). Standard precipitation index (SPI) and stream flow drought index (SDI) are used to decide drought conditions in a watershed and to identify drought-prone areas in the watershed. Temperature projections for both the near and long term indicate an increase compared to the current period under both RCP2.6 and RCP8.5 scenarios. Meanwhile, precipitation projections suggest a decrease for the periods 2040-2060 and 2061-2072 under both RCP2.6 and RCP8.5 scenarios. The standard precipitation index (SPI) and stream flow drought index (SDI) results showed that the watershed experiences mild (-0.5- -0.999), moderate (-1- -1.49), severe (-1.5- -1.99), and extreme (≤ - 2) drought events. Droughts are projected to occur in the periods 2040-2060 and 2061-2072 under both RCP2.6 and RCP8.5 scenarios. Sub-watersheds 7, 8, 9, 10, and 11 showed high vulnerability to severe and extreme drought. Drought-mitigating structures are needed to mitigate drought in the watershed