Using baseflow to quantify diffuse groundwater recharge and drought at a regional scale

Abstract

Although diffuse groundwater recharge is difficult to quantify at a regional scale, baseflow discharge can be used in watersheds with gaining streams with negligible effects from pumping. In Iowa, where these conditions are met, we investigated how watershed-scale baseflow calculated from a network of 132 streamflow gages can be used to quantify spatial and temporal patterns of groundwater recharge across a region; and characterize the emergence and expansion of drought conditions in the state. Mean annual groundwater recharge for the 2000–2017 study period estimated by area-weighting annual baseflow was found to be approximately 220 mm but vary widely from 73 to 467 mm based on precipitation inputs. Recharge was found to be particularly concentrated in the months of March to July which accounted for 66% of the average annual recharge. Baseflow discharged from the drought-impacted headwater basins was highly correlated to U.S. Drought Monitor designations in Iowa headwater basins and thresholds varied among landscape regions due to differences in soils and hydrology. Economic losses due to drought were found to substantially increase when annual groundwater recharge was less than approximately 130 mm yr−1. Overall, study results suggest that regional groundwater recharge and drought susceptibility can be reliably assessed using baseflow available from networked stream gages.