Groundwater Recharge in Northern New England: Meteorological Drivers and Impacts on Low Streamflows

Groundwater recharge is an important component of water availability for drinking water, irrigation, and aquatic habitat. Though northern New England and upstate New York receive relatively consistent precipitation throughout the year, droughts that advance beyond normally occurring low groundwater levels are not an uncommon phenomenon. Meteorological drivers of groundwater recharge for spring (February–June), fall (October–January), and recharge-year (October–June) recharge seasons were evaluated for Northern New England and upstate New York from 1989 to 2018. Net monthly groundwater recharge was computed as the difference between month-end groundwater levels at 21 wells and aggregated by season. Precipitation, temperature, sea-level pressure, 500-mb geopotential heights, and various teleconnection indices were tested against seasonal groundwater recharge using random forest machine learning models. Precipitation within recharge seasons was positively correlated with groundwater recharge for most wells in all seasons. Sea-level pressure and 500-mb heights were typically inversely correlated with groundwater recharge during the recharge-year and fall recharge seasons, when higher values are usually associated with clearer skies and less precipitation. The North Atlantic Oscillation, Pacific-North American pattern and Pacific Decadal Oscillation teleconnections impact groundwater recharge differently by well and season. The influence of groundwater recharge on minimum streamflows at gages close to the study wells, during the subsequent summer/fall, was also analyzed. Summer precipitation was the most important explanatory variable for low streamflows and recharge-year recharge was important for many gages close to the study wells. Summer air temperature was not found to be an important explanatory variable, despite its influence on minimum streamflows through the process of evapotranspiration.