Assessment of spatiotemporal variations of groundwater recharge in the Upper Lerma River basin using a process-based hydrological model

Water resources are under high stress worldwide due to multiple factors. There is a general need to develop better and more efficient management practices. Understanding groundwater and surface water as one source is crucial for this determination. A clear comprehension of groundwater and surface water interactions as an integrated system requires a good knowledge of topography, geology, and climate. This research analyzes the spatiotemporal variation and availability of surface water resources and groundwater recharge in a highland basin using a comprehensive hydrological model. The hydrological model is based on the Soil and Water Assessment Tool (SWAT), allowing spatially distributed assessment using sub-basin and hydrological response units. The case study is the Upper Lerma River basin located in the central part of Mexico. Its location and topography (highland) have made its aquifer the second most source to satisfy the water demand of Mexico City since 1940. As a result, groundwater levels have declined, and springs in the surrounding mountainous regions have progressively disappeared over time. Although few studies attempted to estimate recharge and variability, a lot is unknown to analyze the declining water resources in the basin. This research contributes to understanding the basin water resources using the modeling approach, which integrates topography, land use, soil, and climate data to calculate different water cycle components in space and time. The analysis period is 1985-2017. Statistics of model calibration show a good correlation between the computed and measured discharges from 1995 to 2003 with a Nash-Sutcliffe Efficiency (NSE) value of 0.77, an R² value of 0.79, and a PBIAS of -1%. The preliminary results show that the foothills and alluvial fans are the most extensive recharge areas, which agree with the piezometric data. Detailed analysis on recharge and surface runoff is ongoing.