EL NIÑO – SOUTHERN OSCILLATION AND ITS CORRELATION TO RECHARGE IN COASTAL NORTH CAROLINA

Several studies in the literature demonstrate that climate oscillations such as the El Niño – Southern Oscillation (ENSO) affect precipitation rates in the southeastern United States. Depending on their seasonal timing, they may also affect recharge rates to surficial aquifers in these areas. We analyze the effect of ENSO on precipitation patterns in coastal North Carolina by comparing the Multivariate ENSO Index (MEI) and precipitation rates at several weather stations throughout coastal North Carolina. After categorizing the MEI variations as weak (La Niña), strong (El Niño), and neutral, we then average these values seasonally, normalizing them with seasonal precipitation means.

The timing of these precipitation variations is important in the recharge of coastal aquifers, which receive a majority of their water in winter and early spring. A comparison of the average winter MEI and precipitation power spectra demonstrates a correlation between ENSO and winter precipitation variability in coastal North Carolina. Precipitation and water-level data from a site on Hatteras Island, North Carolina, also suggest that a winter El Niño condition results in higher precipitation rates, thereby causing higher recharge rates and water-table elevations. Our data show an increase in average winter precipitation of approximately 22% during El Niño conditions. Conversely, a winter La Niña condition reduces precipitation rates, thereby decreasing recharge and water-table elevations. Our data show a decrease in average winter precipitation of approximately 20% during La Niña conditions. This 42% variation in winter precipitation based on the winter ENSO condition demonstrates that climate oscillations may ultimately affect the amount of water in the surficial aquifer heading into summer months, when water-table elevations decrease in response to higher evapotranspiration and greater water consumption.