Land Use/Land Cover Changes and Associated Impacts on Water Yield Availability and Variations in the Mereb-Gash River Basin in the Horn of Africa

Climate variability and drought are increasing in the Horn of Africa. Evaluating land use/land cover (LULC) changes and their impacts on water availability and variation are vital for regional land use planning and water resources management. LULC changes during 2000-2015 were estimated using high-resolution Landsat images and the Google Earth Engine cloud platform, and land use dynamic index (K). The impact of LULC change on water yield was evaluated using the Integrated Valuation of Ecosystem Services and Tradeoff (InVEST) model. The results at a regional scale show that there were rapid decreases in the area of forests and barren lands (-K) while there was a drastic increase in the built-up area (+Kvalues). The transition was found to occur from forested land to low and very low biomass areas with 51.13% and 16.7%, respectively. There were similar LULC changes in the Mereb-Gash River Basin. The mean annual water yield increased for all the catchments during 2000-2015 and with the peak in 2005. The highest annual sum water yield decreased in the forested lands from 43.18 million m(3)in 2000 to 4.1 million m(3)in 2015. There was a strong positive correlation between areal changes (%) and the annual water yield variations (%) for all the LULC types except for water body, and the correlation was significantly positive for forest (p < 0.01). The study demonstrates that the decrease in forested areas and expansion in the built-up areas had large impacts on water yield. The impacts may increase pressure on ecosystem services, exacerbate water scarcity, and food insecurity.