The impact of urbanization on groundwater quality and recharge using remote sensing and GIS techniques.

Rapid urbanization has profound impacts on land cover, hydrological processes, and groundwater sustainability, this is a global challenge. This study assessed the influence of urban expansion on groundwater recharge and quality between 2013 and 2024 using an integrated Remote Sensing-Geographical Information System framework in Nnewi, Anambra State, Nigeria. Multi-temporal Landsat imagery, Digital Elevation Models, soil data, rainfall records, and hydrogeological information were processed to derive land-use/land-cover classes and spectral indices including NDVI, NDWI, NBR, and NDBI. Groundwater recharge potential was quantified using a GIS-based multi-criteria evaluation in which land cover, soil permeability, slope, drainage density, and rainfall were standardized and weighted to reflect their relative influence on infiltration. A weighted overlay model generated a recharge index ranging from 0 to 1. Recharge-prone zones cover 27.86% of the study area; however, the mean recharge value of 0.14 and median of 0.00 indicate that most of the landscape has low infiltration capacity, with recharge spatially restricted to limited vegetated and permeable zones. Results revealed substantial environmental changes over two decades. The Normalized Difference Vegetation Index (NDVI) showed a 71.13% decline in vegetation density, while the Normalized Difference Water Index (NDWI) indicated persistently low surface water availability. The Normalized Burn Ratio (NBR) demonstrated increasing land degradation and vegetation loss, whereas the Normalized Difference Built-Up Index (NDBI) confirmed significant urban expansion. Land cover analysis indicated increased impervious surfaces, which now occupy 11.48% of the study area, reducing infiltration capacity. Recharge zones were found to cover 27.86% of the landscape, with a mean recharge potential of 0.14, suggesting limited groundwater replenishment. Urban extent expanded from 51.72% to 57.45%, reflecting an 11.08% growth in built-up areas, strongly correlating with reduced recharge. Water quality analysis revealed spatial variability in physicochemical parameters. Mean concentrations of total dissolved solids, nitrates, and electrical conductivity were higher in densely urbanized zones, and maximum values of some parameters exceeded recommended drinking water limits in localized areas. The Water Quality Index classified parts of the area as good to poor, with poorer quality concentrated near industrial and high-density residential zones. Hence, the findings demonstrate a clear linkage between urban expansion, recharge suppression, and emerging groundwater quality deterioration, providing a basis for sustainable land-use planning and groundwater protection strategies.