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This study was to determine the spatiotemporal characteristics of historical and projected drought events throughout Isiolo County, Kenya, through using self-calibrating Palmer drought severity index (scPDSI). The scPDSI is a complex and robust drought index that applies the water balance model by incorporating the role played by evapotranspiration and soil properties on drought analysis therefore making it appropriate to identify the linkages between meteorological, agricultural and hydrological droughts. The historical scPDSI was computed at a monthly timescale using a 39-year long monthly mean precipitation data from Climate Hazard Group Infrared Precipitation with Station (CHIRPS) and monthly average temperature data from the Climate Research Unit (CRU). The climatological (1950-1996) available water holding capacity (AWHC) of the soil was obtained from Oak Ridge National Laboratory Distributed Active Archive Center (ORNL DAAC) for biochemical dynamics at a spatial resolution of 1o x 1o. The projected scPDSI under Representative Concentration Pathways (RCPs) was computed using bias corrected monthly temperature and precipitation model output data from Coordinated Regional Climate Downscaling Experiment (CORDEX). The datasets were extracted for ten grid points in the County. The scPDSI was used to assess the historical and projected duration, severity, and intensity of droughts. The major significant historical and projected drought events and their characteristics were clearly identified using the run theory. ScPDSI runs have shown that more severe drought events dominated the period between 1980 and 2000. ScPDSI had the longest dry event duration of 61 months and a severity of 126.412 with adverse effects on the eastern locations. The projected drought events identified Mar 2046 –Mar 2048 under RCP4.5 to be the most severe drought lasting for 25 months with severity of 59.292 while under RCP8.5 run Nov 2042 – Nov 2046 is identified as the most severe, 114.362 with the duration of water stress anticipated to last for 49 months. To examine the spatial variability of the drought events in the County, the Empirical Orthogonal Analysis (EOF) was applied to the historical and projected scPDSI time series. The EOF results indicated that the two leading eigen vectors accounted for over 85% of the spatial variability for both historical and projected droughts under the RCPs. Subsequently, the Mann-Kendall (MK) test was applied to the projected scPDSI, temperature and precipitation timeseries in order to determine the local expected drought trends. The MK test of the identified significant increase in trend for temperatures under RCP8.5 and precipitation under RCP4.5 towards the end of the last decade under the study period considered. Both scenarios showed a decline in trends of drought events in Isiolo County from 2020-2050. |
