Development of a model to estimate groundwater recharge

Quantifying the spatial and temporal distribution of natural groundwater recharge is essential for effective groundwater modeling and sustainable resource management. This paper presents M-RechargeCal, a user-friendly software tool developed to estimate natural groundwater recharge using two widely adopted approaches: the Water Balance (WB) method and Water Table Fluctuation (WTF) method. In the WB approach, the catchment area is divided into seven land-use categories, each representing distinct recharge characteristics. The tool includes eighteen different reference Evapotranspiration (ET₀) estimation methods, accommodating varying levels of climatic input data availability. Additional required inputs include crop coefficients for major crops and Curve Numbers (CN) for specific land-use types. The WTF approach considers up to three aquifer layers with different specific yields (for unconfined aquifer) or storage coefficient (for confined aquifer). It also takes into account groundwater withdrawal (draft) and lateral water movement within or outside the aquifer system. M-RechargeCal is process-based and does not require calibration. Its performance was evaluated using six datasets from humid-subtropical environments, demonstrating reliable results (R² = 0.867, r = 0.93, RE= 10.6%, PMARE= 9.8, E_NS = 0.93). The model can be applied to defined hydrological or hydrogeological units such as watersheds, aquifers, or catchments, and can be used to assess the impacts of land-use/land-cover changes on hydrological components. However, it has not yet been tested in arid regions. M-RechargeCal provides modelers and planners with a practical, accessible tool for recharge estimation to support groundwater modeling and water resource planning. The software is available free of charge and can be downloaded from the author's institutional website or obtained by contacting the author via email.