Hydrological Modelling of Surface Runoff and Groundwater Recharge in Semi-Arid Agricultural Watersheds in Katsina State

This study applies hydrological modelling to quantify surface runoff generation and groundwater recharge in semi-arid agricultural watersheds in Katsina State, North West Nigeria, contributing improved water balance estimates essential for sustainable irrigation planning. Semi-arid watersheds in northern Nigeria are characterised by highly variable rainfall, high evapotranspiration demand, and relatively low permeability soils that generate significant surface runoff, yet simultaneously experience declining shallow groundwater tables. Quantitative understanding of water balance components at watershed scale is limited by sparse monitoring networks and inadequate model calibration data. This study applies the SWAT hydrological model to three agricultural sub-watersheds in Daura, Funtua, and Mashi local government areas, covering a combined area of 1,200 square kilometres. Model parameterisation uses soil surveys, digital elevation models from SRTM, land use maps from Sentinel-2 classification, and 25-year daily rainfall records. Calibration and validation use available river flow and groundwater level data. Findings reveal that annual surface runoff averages 18 percent of rainfall, with strong seasonal and inter-annual variability. Groundwater recharge averages 6 percent of rainfall, occurring primarily during high-intensity storms. Climate change scenario analysis projects 15 to 22 percent reductions in groundwater recharge under medium emission scenarios by 2050. The study contributes calibrated SWAT watershed models for the Katsina semi-arid zone and recommends water harvesting infrastructure investments targeted at high runoff generation areas identified by the model.

Keywords: hydrological modelling, SWAT, surface runoff, groundwater recharge, Katsina State.