Spatial modeling of groundwater across land use land cover and climate change gradient using SWAT and Logan's method: a case study of Mbagathi sub-catchment

Groundwater forms the base of all freshwater sources. Its use has significantly increased over the past years and is expected to rise in the future due to its high reliability during drought seasons and continuous depletion of surface water. The great shift towards groundwater abstraction by the urban population and in the Arid and Semi-Arid Lands (ASALs) catchments, which highly experience varying climatic patterns results in falling water tables. The study aimed at modeling groundwater change as a result of the change in Land Use Land Cover (LULC) and climate. The Soil Water Assessment Tool (SWAT) approach and Logan's method were used in analyzing the effects of LULC and climate on groundwater. SWAT simulations provided groundwater recharge rates under present and future land use/land cover and climate-change scenarios. The study showed a significant increase in runoff of 6.3% in 2020 and 13.7% in 2030 and a relative decrease in groundwater recharge of 5% and 3% respectively. The increase in runoff was attributed to the continued increase in urbanization of 12% and decreased vegetation of 9% by 2030 under relatively the same climatic conditions. The study concluded that significant changes in groundwater are realized from the changes in LULC. It is therefore important to preserve vegetative lawns in the urbanized areas to support infiltration, percolation processes hence groundwater recharge to the aquifers.