Evaluation Of Satellite-Based Rainfall Estimates And Application To Monitor Meteorological Drought In Gibe Basin, South West Ethiopia

Abstract

Drought is a natural hazard and a serious problem which is being revealed in most parts of Ethiopia. Meteorological stations in Ethiopia are not as much adequate to monitor drought mainly because of unevenly distributed. However, it could be able to fill this gap through applying satellite rainfall estimation products. Therefore, this study was attempt to evaluate the performance of satellite rainfall product and monitoring meteorological drought in Omo-Gibe basin, South Western Ethiopia. The major data used for the study were Satellite Rainfall Product (CHRIPS, PERSIANN and TMPA), Earth Observation Satellite (eMODIS) and Weather station data from 2000 to 2019. To evaluate the performance of satellite rainfall products statistical analysis (i.e., Pearson correlation coefficient (r), mean error (ME), root mean square error (RMSE), and Bias) were used to evaluate the satellite rainfall products with the corresponding ground observation data at ten independent weather stations. CHRIPS satellite rainfall product was selected as best performance as compared to other satellite rainfall products with r>0.96 at monthly, seasonally and yearly time-scales. TMPA did well next to CHIRPS whereas PERSIANN presented a poor performance under all the criteria. Consequently, the CHIRPS rainfall product was selected and used to assess the spatial and temporal variability of meteorological drought in this study. The 3 month and 12 months SPI values were measured for each grid and used to evaluate the spatial and temporal patterns of drought. The results from SPI values clearly shows that the occurrence of drought was observed during historic drought years (1987-1988, 1991- 1992, 2000, 2002-2003, 2009-2010, and 2015-2016); particularly severe drought occurred in the year of 2002, 2009 and 2016 in the study area. Spatially, southern and central parts of the basin experiences severe drought than north parts. The validity of the result was computed by Vegetation Condition Index (VCI) and Drought Severity Index (DSI) with R2 value of 0.45 and 0.31 respectively. The expected drought occurrences for 3-month timescales in the next 100 years shows that more drought events are expected at Jimma by about 42 times with 15(moderate), 15 (severe) and 12 (extreme) severity classes. Henceforth, the CHIRPS rainfall product can be used as an alternative source of information in developing the grid-based drought monitoring tools for the basin that could help in developing early warning systems.