Severe storms becoming more frequent

December 05, 2007|By Frank D. Roylance | Frank D. Roylance,Sun reporter

Extreme rain and snow storms across the continental United States have become significantly more frequent over the past 60 years, according to a new study that fits in neatly with global warming theory and a decade of work by climate scientists.

A report released yesterday by two environmental action groups found a 24 percent increase in the frequency of days with extreme precipitation between 1948 and 2006, based on a review of weather data from 3,000 observation stations in 48 states.

The authors found the increases were statistically significant in 40 states - but not in six others, including Maryland and New Jersey.

"Scientists tell us that the trend toward more intense precipitation is only beginning," said Tommy Landers, a Maryland organizer for the Environment America Research and Policy Center. The organization published the study with Frontier Group, another public policy research organization.

"If we continue to release greater amounts of global warming pollution each year," Landers said, "we can expect a growing number of extreme storms in the future."

Floods have caused more death and damage in the 20th century than any other natural disaster, experts say. And heavy rain or snow does not always make more water available for human use. In fact, global warming theorists predict more frequent heavy storms, but also more widespread drought.

The study's release yesterday was the latest in a series of reports by environmental groups seeking to influence public debate over global warming. This includes a possible vote in the Senate this week on proposed global warming legislation contained in the Lieberman Warner Climate Security Act.

Global warming theorists and climate modelers say warming oceans will mean more evaporation, and that a warmer atmosphere will hold more of that moisture. But when weather conditions are right, those clouds will be more likely to unload their extra moisture as heavy rain or snow.

With technical guidance from the U.S. Climatic Data Center and the Illinois State Water Survey, the study's authors started by identifying the severity of a rainfall or snowfall that would be reached only once a year, on average, at a given location.

Then they analyzed how often that magnitude of rain or snow storm, or larger ones, actually occurred between 1948 and 2006.

They found that the frequency of such storms has risen, on average, across the country. Only Oregon, Florida and Arkansas saw declines in the frequency of such storms. Of those, only Oregon's decline was deemed statistically significant.

The steepest increases - in excess of 50 percent - were recorded in New York and New England. As a region, New England experienced an increase of 61 percent in such storms, followed by the Mid-Atlantic region (defined here as New York, New Jersey and Pennsylvania) at 42 percent.

Maryland was grouped with the South Atlantic states, which collectively saw a 15 percent increase in the frequency of these extreme storms.

The report's findings are not entirely new and are also consistent with the conclusions of the Intergovernmental Panel on Climate Change, said David R. Easterling of the National Climatic Data Center.

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