Assessing groundwater recharge of a shallow aquifer in an urbanized area

Groundwater, which accounts for the majority of the world’s accessible freshwater, is vital for global water security, integral to the hydrological cycle, and supports various human activities. Its sustainable management is increasingly crucial. In urban environments, factors such as vegetation suppression, soil impermeabilization, and drainage systems often limit groundwater recharge and infiltration capacity. To quantify groundwater recharge in these areas, we developed and tested a simplified and intuitive methodology that integrates a spatially explicit groundwater recharge index with transient numerical simulations. The recharge index delineates groundwater recharge zones based on a hierarchical combination of surface coverage (imperviousness), topographic slope, and soil characteristics. Subsequently, we employed a transient numerical groundwater flow model to calibrate recharge values assigned to each defined zone, ensuring consistency with observed water table fluctuations measured in the field. This approach provides a practical balance between methodological simplicity and spatial accuracy, facilitating application even in data-limited regions. This approach identified four distinct groundwater recharge zones in a small urban area of Rio Claro, southeastern Brazil. The model, calibrated with time-varying hydraulic head data from 29 monitoring wells, indicated that groundwater recharge represents an average of 7.7% of local precipitation, with a recharge rate of approximately 119 mm/year. Importantly, groundwater withdrawals from a supply well in the area accounted for only 3.5% of the total recharge, suggesting that, despite substantial reductions in recharge due to soil impermeabilization, the current groundwater extraction volume remains sustainable.