Spatio-temporal characterisation of droughts using selected indices in Upper Tana River Watershed, Kenya

Abstract Monitoring and assessment of drought is key to modelling, impact assessment, mitigation and prediction of occurrence. The Upper Tana River watershed hosts two of Kenya's main water towers, Mt. Kenya and Aberdare Ranges, and is increasingly under threat from reduced water levels in the river basins due to unsustainable anthropogenic activities. The occurrence of drought in the region often exacerbates the impact of such activities on the natural resource-base. The study evaluated temporal and spatial characteristics of meteorological drought in Upper Tana Watershed using remotely sensed data from 1981 to 2018. Climate Hazard Group InfraRed Precipitation with Station (CHIRPS) and Modern-Era Retro-Analysis for Research and Applications-Assimilation Model (MERRA) products provided precipitation and temperature data via Google Earth Engine platform. GeoClim was used in the retrieval of Standardized Precipitation Index (SPI), while Standardized Precipitation and Evapotranspiration Index (SPEI) data were downloaded from SPEI Global Drought Monitor. Values for these datasets were plotted against time to facilitate temporal analysis of the drought. Spatially, the most intense meteorological drought period was from 2007 to 2009 in that the years were hit by severe drought for three consecutive years that covered the entire watershed. Temporally, drought incidences were observed in 1982, 1989, 1994, 2000, 2006, and 2011 and 2017. Both SPI and SPEI indices showed similar drought years. Drought mitigation measures should be implemented across the watershed. The findings provide insights that can be used by natural resource management practitioners in; drought forecasting, early warning systems, and in planning and management of water resources within the watershed. We recommend characterisation of the other types of droughts, agricultural and socio-economic droughts, for a holistic understanding of their spatial-temporal manifestations and the impact on the livelihoods of the watershed.