SEASONAL GROUNDWATER LEVELS PROVIDE EVIDENCE OF RECENT CLIMATE CHANGE IN THE NORTHEASTERN US

Groundwater levels in unconfined aquifers provide an analog of regional climate by reacting to temperature, precipitation and snowmelt. The combination of these elements produces a sinusoidal annual cycle with predictable highs and lows. This study examines the seasonal groundwater and precipitation cycles for unconfined aquifers at Ft. Kent, ME and Haverhill, MA. Regional climate warming is already disrupting the historic seasonality of the region by causing spring to occur earlier (Schwartz, 2006) and decreasing the snow/rain ratio (Huntington et al., 2004). Groundwater levels record these changes as a forward shift in the annual cycle. At Ft. Kent, where there have been great changes in precipitation patterns since the late 1970's, the groundwater cycle shift is already obvious, and is easily distinguishable from a simple increase in annually averaged levels. The change corresponds well with the coupled precipitation record from the site. There is a declining snow/rain ratio at Ft. Kent in addition to a strongly linear increase in annual precipitation. Both of these trends have been observed at other northern New England locations. Haverhill, while showing a similar, but weaker increase in annual groundwater levels does not show the same pronounced cycle shift, indicating a minimal change in seasonality. The site has a weakly correlated increase in precipitation, and no noticeable decrease in the snow-to-rain ratio. Current model projections for the northeast call for average temperature increases of 2.7C -5.7C by the end of the century in addition to dramatic increases in precipitation (Hayhoe et al., 2007). This study provides a scale for the shift in seasonality associated with the temperature and precipitation increases. The use of groundwater levels to track climate change driven seasonality changes may be extremely useful in areas with long groundwater records.

References:

Hayhoe, K., Wake, C. P., Huntington, T. G., Luo, L., Schwartz, M. D., Sheffield, J., et al. (2007). Past and future changes in climate and hydrological indicators in the US northeast. Climate Dynamics, 28(4), 381-407.

Huntington, T. G., Hodgkins, G. A., Keim, B. D., & Dudley, R. W. Changes in the proportion of precipitation occurring as snow in new england (2004). Journal of Climate, 17(13), 2626-2636.

Schwartz, M. D., Ahas, R., & Aasa, A. (2006). Onset of spring starting earlier across the northern hemisphere. Global Change Biology, 12(2), 343-351.