Study: Climate change means more heavy rain

by Doyle Rice, USA TODAY, August 21, 2009

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Record rainfall led to disastrous flooding across much of Iowa in 2008, including the town of Cedar Rapids. Scientists say climate change will lead to an increase in heavy rainfall events for most of the world. By David Greedy, Getty Images

Climate change will lead to an increase in heavy rainfall events across most of the world, according to a study published this week in the peer-reviewed journal Proceedings of the National Academy of Sciences by researchers at the Massachusetts Institute of Technology and Caltech.

The computer models used in the study predict that areas such as North America can expect a significant increase in heavy rain.

How much rain? The study suggests that precipitation in extreme events will increase by about 6% for every 1.8 degree rise in global temperature. A global temperature increase of anywhere from 2 to 11 degrees is expected by 2100, according to the Intergovernmental Panel on Climate Change.

Overall, while the pattern is clear and consistent outside of the tropics, climate models give conflicting results within the tropics so more research will be needed to determine the outcomes in those regions.

The primary reason for the precipitation increase is that warmer air can retain more water vapor than cooler air. So as the climate heats up, "there will be more vapor in the atmosphere, which will lead to an increase in precipitation extremes," says study co-author Paul O'Gorman of MIT.

Some of the most notable dangers of the additional rainfall include flooding and soil erosion.

This study follows on the heels of another one I reported on in the summer of 2008 about increased rainfall being a likely outcome of global warming. That research, published in the peer-reviewed journal Science, found that extreme precipitation events are already increasing as the globe warms and was the first actual, observed evidence of the link between climate change and more powerful rainstorms.

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Meanwhile, the Climate Prediction Center has come out with its fall forecast for the USA. (That includes the months of September, October and November, which climatologists refer to as fall.) As seen in the map to the left, the Southwest, Northeast, and Alaska have the highest chances of seeing a warmer-than average autumn. No U.S. regions are expected to be cooler-than-average.

As for precipitation, the areas likely to see a wet fall are along the Gulf Coast and Florida, in the central Plains, and the south coast of Alaska. The only region where a dry fall is likely is in the Pacific Northwest.

Link: http://www.usatoday.com/weather/climate/2009-08-21-climate-change-rain_N.htm