April 6, 2010

Northeast Rainfall Has Increased Over 60 Years

A new study has found that the Northeast is seeing more frequent "extreme precipitation events" in line with global warming predictions, including storms like the recent ones that have brought floodwaters to neighborhoods and businesses across New England.

The study does not link last week's devastating floods to its research, however it looked at 60 years' worth of National Weather Service rainfall records in nine Northeastern states and discovered that storms that produce an inch or more of rain in a day are occurring more often.

"It's almost like 1 inch of rainfall has become pretty common these days," said Bill Burtis, spokesman for Clean Air-Cool Planet, a global warming education group that released the study Monday along with the University of New Hampshire's Carbon Solutions New England group.

UNH associate professor Cameron Wake said the study's results are consistent with what could be expected in a world warmed by greenhouse gases.  However, he did acknowledge it would take more sophisticated studies to cement a warming link.

"I can't point to these recent storms and say, that is global warming," he told the Associated Press (AP).

Researchers said the potential economic impact is more certain if the 60-year trend continues and requires billions of dollars in infrastructure improvements to things in the region like roads, bridges, sewers and culverts.

The study used precipitation data from 219 Weather Service reporting stations in Connecticut, Maine, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island and Vermont from 1948 to 2007.

The study discovered that in all but 18 of the stations, "extreme precipitation events," defined as storms that produced at least an inch of rain over a 24-hour period or the water equivalent of snow, are occurring at a more frequent rate.

Average annual precipitation increased by nearly three-quarters of an inch per decade over the 60-year period.  That period included a marked drop-off in rainfall during the 1960s, when much of New England experienced drought, and again during a regional drought in 2001.

The study also found that the storms which produced 2 to 4 inches in a 24-hour period occurred more regularly than in the past.

Wake said that as the world warms, there is more energy to evaporate water, creating more water vapor in the air.  He said that as a result, that can increase the number of storms and the amount of precipitation those storms produce.

The March storms seem out of whack even with the findings in the report.  Providence, R.I. and other cities set a monthly record for precipitation, while Boston experienced its second-rainiest month since record keeping began.

"It's consistent, but it's way more than even the trends we've seen," he said. "It's anomalous for sure."

Global warming skeptic Patrick Michaels told AP that it would be unfair to use the recent floods as an example of what's in the study. 

"You can't take an individual event and say it's a product of a certain trend," Michaels said.

Michaels, a senior fellow in environmental studies at the Cato Institute, said previous studies have shown that New England's wettest days of the year are getting wetter over time, but there was no net change nationwide, raising doubt as to whether global warming is the culprit.

Some experts say that whether warming is the cause or not, if rainstorms are getting fiercer, there will be a price to pay.

"If you're spending more on dealing with extreme weather events, what does that take away from?" said Ross Gittell, an economics professor at UNH and executive committee member of Carbon Solutions New England.

"Do you have to tax people more and that has a damper on the overall economy?" he said. "... Or does it take away from investments in education that could lead to more productivity and economic growth over time?"


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