Study Details Links Between Climate, Groundwater Availability – Will Help Water Managers Prepare For Drought

Everyone knows that climate affects our water supply, but new research from North Carolina State University gives scientists and water-resource managers an unprecedented level of detail on how climate and precipitation influence groundwater and surface water levels in the Southeast.

Researchers found that the groundwater, primarily from unconfined aquifers, available in any given month is directly influenced by the amount of precipitation that fell in that watershed three months earlier. For example, groundwater levels in April are affected by precipitation that fell in January.

Similarly, streamflow – the amount of water in rivers, streams and other surface waters – is influenced by overall groundwater levels over the previous three months combined. So  streamflow in April is influenced by groundwater levels in January, February and March.

“This is the first time we’ve had this specific understanding of how climate and precipitation influence groundwater and streamflow in the Southeast,” says Dr. Sankar Arumugam, co-author of a paper describing the study and an associate professor of civil, construction and environmental engineering at NC State. The researchers looked at the Southeast region of the United States, stretching from Virginia to Florida and westward to include Alabama.

“Our findings give water-resource managers significantly more information they can use to make planning and policy decisions to better prepare for water shortages or drought by developing management plans that account for both streamflow and groundwater,” Arumugam says.

The researchers evaluated 20 to 30 years of data from 20 watersheds throughout the Southeast, as well as climate data from the El Nino Southern Oscillation – which denotes hot (El Nino) or cold (La Nina) sea-surface temperature conditions in the tropical Pacific.

The paper, “Role of Climate Variability in Modulating the Surface Water and Groundwater interaction over the Southeast United States,” is available online from the Journal of Hydrologic Engineering. The paper was co-authored by Dr. Naser Almanaseer, a former Ph.D. student at NC State who is now on faculty at Al Balqa Applied University in Jordan. The research was funded by an early career grant from North Carolina Sea Grant, NC State’s Water Resources Research Institute, and by a National Science Foundation CAREER grant.

NC State’s Department of Civil, Construction and Environmental Engineering is part of the university’s College of Engineering.

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Note to editors: The study abstract follows.

“Role of Climate Variability in Modulating the Surface Water and Groundwater interaction over the Southeast United States”

Authors: Naser Almanaseer, A. Sankarasubramanian, North Carolina State University

Published: online, Journal of Hydrologic Engineering

Abstract: We investigate the role of climatic variability on interannual groundwater and streamflow variability in the Southeast U.S. For this purpose, streamflow and associated groundwater levels are analyzed for 20 basins that are minimally affected by reservoirs and groundwater pumping. Using the spatially-averaged monthly precipitation time series obtained from the Precipitation Regressions on Independent Slope Model (PRISM), we identify the recharge and discharge periods that influence the groundwater levels during the winter (January-February-March, JFM) and summer (July-August-September, JAS) seasons. Recharge-discharge dependency analyses indicate that precipitation during the previous three months influences the groundwater level in a given month. Streamflow in any given month depends on the groundwater level during the previous three months. Principal component analysis (PCA) on the precipitation, temperature, streamflow and groundwater data indicate that groundwater levels and streamflow are the two dominant variables influencing the basin hydroclimatology. Further, relating the percentage variance explained from the PCA to baseflow index (BFI) clearly shows that basins with high BFI have higher eigenvalues, indicating that groundwater is a spatial integrator of hydroclimatic processes. Relating the groundwater levels with El Nino Southern Oscillation (ENSO) index, Nino3.4, shows that interannual variability in JFM groundwater levels could be partially explained by the ENSO conditions, but the relation between JAS groundwater levels and JAS Nino3.4 is not statistically significant. Precipitation forecasts from ECHAM4.5 General Circulation Model indicate that it is possible to quantify groundwater availability during the winter season based on the forecasted precipitation and ENSO conditions.