Role of Climate Variability in Groundwater-Surface Water Interactions over the Southeast United States

Groundwater-surface water interaction is a complex process that is controlled by several hydroclimatic attributes and basin characteristics. The complexity of this interaction originates from the temporal and spatial variability of hydrogeologic system and from the external forces such as climatic variations. This research seeks to understand the role of climate in modulating groundwater-surface water interactions and to better utilize this relationship in predicting seasonal to interannual streamflow and groundwater availability. To investigate this, we selected 20 basins with limited anthropogenic influences within the Southeast United States to represent the broad climate, surface and subsurface hydroclimatic over the selected region.;The study performs a detailed dependency analysis among basin-level precipitation, temperature, streamflow and groundwater to identify recharge and discharge periods that influence the seasonal streamflow and groundwater interaction. Based on this analysis, the most dominant variable for each season is identified using singular spectrum analysis (SSA) on the recharging months of precipitation, and discharging months of streamflow along with groundwater and temperature. Findings from SSA clearly indicate that groundwater and streamflow are the two critical variables influencing the basin hydroclimatic variability in comparison to precipitation and temperature. Relating the eigenvalues with baseflow index shows that significant groundwater discharges are associated with larger eigenvalues which indicate the role of groundwater as a spatial integrator of hydroclimatic process. Further, basins with higher Baseflow Index (BFI) show higher eigenvalues, which indicate that groundwater is a spatial integrator of hydroclimatic processes. On the other hand, relating groundwater levels to El Nino Southern Oscillation (ENSO) index, Nino3.4, shows that the interannual variability in winter groundwater levels can be partially explained by the ENSO conditions. Associating precipitation forecasts from ECHAM4.5 General Circulation Model with winter groundwater levels indicates that forecasted precipitation and ENSO conditions can be used to quantify groundwater availability during the winter season over the Southeast U.S.;To evaluate the potential in predicting groundwater and streamflow using precipitation forecast at seasonal and monthly time scales, we consider Flint River Basin, Georgia. For this purpose, we developed statistical and physical prediction models to examine the potential in using precipitation forecasts as a primary predictor in predicting streamflow and groundwater. Results show that incorporating precipitation forecasts can significantly improve the skill of the developed prediction models at seasonal and monthly time scales. Collectively, this research summarizes the relationship between climate and groundwater over the Southeast U.S. and demonstrates the utilization of precipitation forecasts in predicting seasonal groundwater.