The frequency of flooding in New England has substantially increased over the past 70 years, but when flooding has occurred, it has been on average shorter in duration and less intense, concludes a surprising new study published at Geophysical Research Letters.

Between 1940 and 1970, flood events in New England occurred about two times per year. But from 1971 to 2013, that number jumped to about five times per year, a rise in flooding observed nowhere else in the country.

When comparisons are made across other regions of the country, no consistent pattern in flooding can be observed. For example, in the Mississippi Valley and Great Plains, there has been a slight decrease in the frequency of flooding, but a large increase in their duration and intensity.

The differing trends across regions are unexpected, since it has long been assumed that heavier precipitation and warmer temperatures from climate change were not only making floods more likely but also increasing their severity. However, based on the observable historical record, the authors of the recent study conclude that climate change does not yet seem to be influencing U.S. flood patterns in a consistent direction.

Scientists at the U.S. Geological Survey in collaboration with researchers at the Vienna University of Technology in Austria examined shifts in U.S. flood duration, frequency, magnitude and volume for the period 1940 to 2013. They analyzed data collected from 345 stream gages scattered across states and regions.

“Precipitation doesn’t always cause floods, so sometimes it might rain but it won’t cause flooding because there may be not enough, for example,” said Stacey Archfield, a U.S. Geological Survey scientist and leader of the team that wrote the report. “In New England, one hypothesis one might put out [relative to the differential increase in flooding] is that it may be related to snowfall.”

Preparing for the Future

Archfield hesitates to speculate about what might be expected in the future, since their analysis is based entirely on the historical record of flooding.

“We approached this study because there were some regional analyses we wanted to look at from a national level to see if the flooding patterns across the Northeast were widespread or not,” she says. “For good reason, those few regions were picked for intense study because people in those regions noticed changes.”

She adds that the data from their study can be used as a starting point to assess and prepare for future flooding in specific regions such as New England.

“I know in New England, for sure, this is an important issue for them that they need to grapple with. So the question is how do we adjust? When do we make an adjustment? How certain are we of change in the future?” she says. “I think one thing this study shows is that a uniform approach is probably not going to be applicable across the United States, and a nuanced approach is what we should be thinking about.”

–Adam Tismaneanu is a fourth-year student at Northeastern University where he is studying journalism, media & screen studies. He has previously written for TechTarget’s SearchFinancialApplications site and Northeastern Journalism Abroad in Spain. 

See also:

New England tidal marshes are disappearing as sea levels rise, warns new study 

Rising seas could weaken New England septic systems, contaminating well water in coastal areas