Role of Interannual Climate Oscillations on Coastal Groundwater Conditions in North Carolina

Multi-year climate oscillations such as the El Niño – Southern Oscillation (ENSO) affect precipitation and stream discharge rates in areas of the southeastern United States including North Carolina, a state where decades of rapid population growth has combined with considerable drought in recent years to create serious water supply management problems. While inferences may be drawn between these hydroclimatological relationships and groundwater conditions, little work has been done to explicitly link groundwater conditions to interannual cycles, and none has examined the influence of these signals on groundwater in the southeastern United States. Here we investigate relationships between winter conditions of ENSO, based on the Multivariate ENSO Index (MEI), and lagging baseflow rates in North Carolina. We find strong correlation between winter ENSO and lagged baseflow in the coastal fringes of eastern and southeastern North Carolina. These correlations, and anomalies in mean winter baseflow between the upper and lower quartiles, decrease rapidly with distance inland from the coast. Simulations of groundwater flow and solute transport within a cross-section through Hatteras Island, North Carolina, moreover, indicate that these anomalies extend to coastal groundwater, and may provide an interannual oscillation that influences the morphology of the mixing zone. Our results demonstrate that interannual climate oscillations in the Pacific Ocean have a strong effect on hydrological processes in eastern North America, and that these effects persist despite the filtering provided by the groundwater flow process. These results have implications for water resource availability in many regions where water management is complicated by population growth and climatic uncertainty, demonstrating that in one such region significant variability in groundwater supply may be explained by distant climate phenomena.