Baseflow sensitivity to historical and potential future drought scenarios in the Delaware River basin

Study region: The upper and middle Delaware River basin (UMDRB), USA Study focus: Baseflow is an important component of human and ecological water supply especially during meteorological drought, when streamflows are controlled by the shallow subsurface hydraulics governing the release of stored groundwater. Although previous studies have examined drought propagation through the landscape, this study integrates a unique high-resolution atmospheric model with coupled groundwater/surface water (GW/SW) modeling to compare the regional baseflow response across historical and potential future drought severities in a managed basin. We developed a GW/SW model for the UMDRB where human and ecological needs compete for drought baseflows. The calibrated model reproduces the landscape and subsurface response to the regional drought of record and was used to predict baseflows under a simulated future recurrence of that drought. New hydrological insights for the region: Results indicate that the magnitude and timing of winter recharge will likely change during a future recurrence of the historical drought resulting in lower water tables that lead to lower baseflow discharge and reduced riparian evapotranspiration. Future baseflows were 25% less than historical baseflows at their respective lowest extremes, suggesting that the historical experience can be an effective upper limit for what may recur. Results also indicate that preferential recharge – a process that requires better basin-wide characterization – could be an important mechanism of sustaining groundwater levels and baseflow.