Atmospheric effects on variability and seasonality of groundwater levels in the Eastern U.S.

Abstract:

Natural variations in water resources are often thought of as reflecting seasonal and interannual forcings in atmospheric water fluxes. Such variations are readily observed in streamflows in response to precipitation and lags due to basin water storage. These forcings also result in time-varying infiltration into the subsurface and variable aquifer recharge. Low-pass filtering in the subsurface, which can retain seasonal and interannual variability in hydrologic inputs but remove high-frequency variability, can modify responses of groundwater systems to precipitation forcings. Because of the filtering, we hypothesize that groundwater relations to seasonal and interannual precipitation forcing may possibly have greater statistical significance than relations between streamflow and precipitation. To quantify the relations, we correlate monthly time series of groundwater and streamflow in the eastern United States (US) to precipitation and climate indices. We focus on interannual differences in seasonal groundwater level highs and lows in wells to evaluate how precipitation affects groundwater extreme conditions in any year. To quantify differences in climatic and hydrogeologic settings, we correlate the spatial and temporal patterns from empirical orthogonal function analysis of the seasonal groundwater anomalies to precipitation and climate indices. Results indicate a north-south gradient in significant relations (95% confidence) between seasonal high anomalies to the El Nino/Southern Oscillation as indicated by the Multivariate ENSO Index (MEI), with stronger relations in the southern and northern parts of the eastern US. Preliminary results indicate that relations between groundwater and MEI are more significant than previously thought. Additional analysis will examine, through statistical analysis and modeling, if the low-pass filtering of high-frequency variability of hydrologic inputs in the subsurface allows for clearer teleconnection between groundwater and climatic modes.