Groundwater quality dynamics and hydrochemical indicators of water insecurity in the semi-arid Sokoto Basin, Northwestern Nigeria

Abstract Groundwater is the surest water source in semi-arid regions, where surface water is seasonal and subject to climatic fluctuations. Growing climatic stress, along with anthropogenic pressures, in the Sokoto Basin of northwestern Nigeria poses a threat to groundwater quality and the region's water security. This paper has explored groundwater hydrochemistry and identified significant hydrochemical predictors of water insecurity across different geological environments in the Western Sokoto Basin. Fifty-four groundwater samples were collected from hand-dug wells and boreholes in the basement complex and sedimentary formations. The analysis of physicochemical and heavy-metal parameters was performed according to the standard APHA (2017) methods, and multivariate (PCA, HCA, correlation) and geostatistical (Ordinary Kriging, variogram modelling) analyses were used to demonstrate spatial patterns, controlling factors, and predictive accuracy. Findings indicate that groundwater quality differs considerably with lithology: basement complex aquifers are more mineralised and enriched in metals (Mn, Cr, Al, Zn, As) than sedimentary rocks, mainly due to extended water-rock interactions, weathering, and climatic concentration processes. Spatial interpolation revealed unique hot spots of contamination, especially in low-lying and high-evaporation areas, suggesting a magnifying effect of climate stress on solute buildup. High predictability (R 2 > 0.9 in most metals) of kriging models and uncertainty zones (as revealed by nRMSE mapping) was observed in areas of hydrochemical instability. Theoretically, the research will enhance geostatistical understanding of groundwater dynamics in data-limited, climate-sensitive basins by integrating climatic, geological, and geochemical factors into a single explanatory model. In practice, the results deliver early-warning hydrochemical indicators to track groundwater insecurity and can be used to enable evidence-based interventions to meet Sustainable Development Goal 6. The research suggests that semi-arid West African areas should sustain groundwater use through continuous spatial surveillance and adaptive management to enable safe, climate-resilient groundwater use.