A new approach combining groundwater storage change (GWSC) derived from Gravity Recovery and Climate Experiment (GRACE) satellite data and baseflow was proposed to estimate groundwater recharge at large spatial scales but a short (monthly) time scale. This method was applied in two typical karst basins of southwest China, the Wujiang River basin (WRB, ∼87,900 km 2 , ∼70% karstification) and Xijiang River Basin (XRB, ∼360,000 km 2 , ∼44% karstification). The 2006-2012 monthly baseflow was first separated from in situ streamflow through multivariate regression analysis. Groundwater recharge was estimated using separated baseflow and GWSC estimated from GRACE data and observation-based groundwater-level data. The comparison between GRACE-and observation-based recharge in the larger XRB shows better consistency, while that in the smaller WRB shows larger discrepancies. Considering the associated uncertainty (60-93 mm/yr), the 2006-2012 mean recharge in two basins, ranging 199-225 mm/yr (17%-19% of precipitation) is comparable to bulletin-reported estimates (∼145 mm/yr). Both the degree of karstification and aquifer water table depth influence recharge and discharge processes in karst areas of southwest China. The more karstic WRB exhibits more rapid infiltration (due to more developed permeable epikarst zone) and higher discharge capability (due to more developed underground drainage systems), particularly during dry periods (2009, 2011, and winter). Baseflow exhibits a shorter time lag to recharge and GWSC in the XRB than WRB owing to more quick flow, lower storage with more rapid infiltration, and shorter mean groundwater residence time. Observation-based monthly recharge reflects different rainfall-infiltration-runoff processes under different rainfall intensities, particularly in the WRB.
Plain Language SummaryGroundwater recharge is a critical water budget component. This study proposed a new method to estimate groundwater recharge at large spatial scales but on a short time scale. This method combines the groundwater storage changes estimated from gravity satellite data and baseflow (i.e., the main groundwater discharge component) separated from in situ streamflow through multiple regression analysis. We applied this method in two karst basins in southwest China, the Wujiang and Xijiang River Basins. We validated groundwater recharge estimates from gravity satellite data against those only from ground observations. At a larger scale in the Xijiang River Basin, the satellite-and ground-based estimates of groundwater recharge showed better agreement. In the Wujiang River Basin, relatively more rainfall infiltrated into the subsurface to form recharge and more groundwater drained out during dry periods because this basin has a larger proportion of karst areas where the underlying rocks were eroded with large voids and spaces to transfer water. In the Xijiang River Basin, the groundwater storage requires less time to drain out to form baseflow because the flow velocity in this basin is faster. Compared to the gravi...