Groundwater recharge estimation under changing climate and land use scenarios in a data-scarce Bahi (Manyoni) catchment in Internal Drainage Basin (IDB), Tanzania using Soil and Water Assessment Tool (SWAT)

Abstract

Spatio-temporal studies of groundwater recharge establish a groundwork for comprehending the effects of climate and land use change on groundwater resources, particularly in areas where groundwater is a primary source of water such as the Internal Drainage Basin (IDB), Tanzania. Therefore, quantification of groundwater recharge for years the 2050s and 2080s was executed using the SWAT in Bahi (Manyoni) Catchment (BMC) in IDB. Shared Socioeconomic Pathways (SSPs) climate scenarios particularly SSP245 as medium emission and SSP585 as high emission scenario were used. Monthly calibration and validation of the SWAT model were performed by using streamflow data from a gauged sub-catchment within BMC. Obtained Nash-Sutcliffe Efficiency (NSE) for the calibration period from 1971 to 1982 was 0.79 and for the validation period from 1983 to 1990 was 0.69. Later, performed another validation using actual evapotranspiration in an ungauged BMC achieved NSE of 0.59. The findings from calibrated model depicted, under the impact of climate change alone, it was estimated that there will be a slight increase in overall annual average groundwater recharge of 3.05 mm/y under SSP245 and to 5.12 mm/y under SSP585 in year 2050s whereas under collective impact of climate and LULC change an increase of 2.31 mm/y under SSP245 and of 3.98 mm/y under SSP585 in year 2080s from a baseline of 4.5 mm/y in 1980s. This indicates the impact of LULC alone to be trivial. In the steep slope areas, the catchment with 15% reduced rainfall will experience lower recharge of up to 24% whereas gentle slope areas with a 25% increase in rainfall will experience a recharge of up to 123% compared to the baseline period. Established groundwater recharge zones give imperative information to IDB managers in relation to water management plans to optimize future groundwater recharge.