Risk for New England Floods Rises with Water Tables

Hydrogeologist David Boutt, an expert in the mechanics and flow paths of subsurface water, with UMass Amherst graduate student Kaitlyn Weider, recently published in the journal Geophysical Research Letters the first instrument-based, long-term compilation and evaluation of the water table at a regional level over the last 60 years in New England. Evidence suggests that climate change is modifying the timing and nature of precipitation and altering the hydrogeologic cycle, the researchers say.

It is widely accepted that rising temperatures and the timing of rain and snowfall in New England are changing the character of the seasons, but there has been little study of how this might affect regional surface and ground water levels, Boutt notes. Variables such as streamflow, lake levels and timing of peak low and high flows are continually changing and could well be affected, he adds.

Using data from wells, stream gauges, precipitation monitors and weather-station temperatures collected between 1940 and 2010, he and Weider compiled the outlook for New England. They also show how researchers in other areas can use such information with statistical modeling and analyses to assess risk in their region.

Boutt and Weider collected ground water data from nearly 100 wells with at least 20 years of continuous monthly records in the Climate Response Network from various geologic and climatic regions of Maine, New Hampshire, Vermont, Massachusetts, Connecticut and Rhode Island. Overall, 78 percent of these sites provided at least 40 years of data.

They used precipitation and temperature data from the National Oceanic and Atmospheric Administration’s National Climatic Data Center and the U.S. Historical Climatology Network, totaling 43 temperature sites and 75 precipitation stations. They took surface water flow information from 67 stream gauges, as well.

Boutt and Weider examined New England 12-month average ground water, streamflow, precipitation and temperature for statistically significant trends and departures. They report that precipitation, streamflow and ground water levels remain relatively stable throughout their records until the last 10 years, when they observe “consistently above normal precipitation, streamflow and ground water levels.”

The analysis suggests that changes in precipitation over timescales greater than a single year can lead to a build-up of water storage in the subsurface. This excess water can be stored for many years in the sub-surface, resulting in essentially what is a memory-effect of previous wet and dry periods.

Overall, results show that all variables are producing significant increasing trends for the New England region, Boutt says. He and Weider summarize that their analysis of New England climate anomalies from 1940–2010 depicts “a strong relationship between climate variables and ground water levels displaying intriguing decadal patterns that reveal information about the sensitivity of aquifers to climate perturbations.”