The process by which water moves downward from the surface through the unsaturated zone to replenish an aquifer. It is the primary mechanism for sustaining groundwater resources.
Groundwater recharge is the hydrologic process by which water percolates downward from the land surface through the unsaturated (vadose) zone to reach the water table and replenish aquifer storage. Natural recharge occurs through diffuse infiltration of precipitation, focused recharge from streambeds and lakes, and mountain-front recharge where runoff from highlands enters alluvial aquifers. Recharge rates vary enormously depending on climate, soil type, vegetation, topography, and geology, ranging from less than 1 mm/year in arid regions to over 500 mm/year in humid areas with permeable soils. Estimation methods include water balance approaches, chloride mass balance, water table fluctuation analysis, lysimeter measurements, and numerical modeling. Managed aquifer recharge (MAR) involves intentionally augmenting groundwater supplies through infiltration basins, injection wells, or enhanced streambed infiltration. Understanding recharge is fundamental to sustainable groundwater management because long-term pumping rates should not exceed recharge rates to avoid aquifer depletion. Climate change projections suggest that recharge patterns may shift significantly in many regions due to changes in precipitation intensity, seasonality, and temperature.