ALBERT

Description: Because groundwater is an essential resource for people and ecosystems, a better understanding is needed of the fundamental controls on recharge and its interactions with vegetation change. We analyzed 〉600 estimates of groundwater recharge to obtain the first global analysis of recharge and vegetation types. Globally, croplands had the highest proportion of water input (WI = precipitation + irrigation) that become recharge, followed by grasslands, woodlands, and scrublands (average proportional recharge: 0.11, 0.08, 0.06, and 0.05, respectively; P 〈 0.0001). A stepwise regression model revealed that WI had the strongest association with recharge overall, followed by vegetation type, potential evapotranspiration (PET), saturated hydraulic conductivity based on soil texture (Ks), and seasonality of rainfall (R2 = 0.29, 0.16, 0.12, 0.06, and 0.01, respectively; P 〈 0.0001). Recharge increased with increasing WI, Ks, and seasonality of rainfall and decreased with increasing PET. Relative differences in recharge among vegetation types were larger in drier climates and clayey soils, indicating greater biological control on soil water fluxes under these conditions. To further test the relationship between recharge and vegetation, we compared global synthesis data to our parallel field estimates of recharge in paired grasslands, croplands, and woodlands across the Argentinean Pampas and the southwestern United States. Our field estimates of recharge were similar to, and followed the same pattern of, recharge under vegetation types in the synthesis data, suggesting that land-use changes will continue to alter recharge dynamics and vadose zone processes globally. The results of this study highlight the implications of land-use management for sustainable groundwater use and should also help test and improve recharge estimates in large-scale water balance and climate models.