US could face tough tornado season in 2012 - experts

Wed Feb 22, 2012 3:26pm EST

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* Climate change could fuel tornado-making storms

* 2011's disasters caught insurers off guard

By Deborah Zabarenko

WASHINGTON, Feb 22 (Reuters) - One year after a deadly tornado season in the United States caused nearly $30 billion in damage, an above-normal number of twisters could be in store for 2012.

While there is no way to predict that there will be a repeat of 2011's calamitous series of tornadoes, private weather forecaster Accuweather.com said this week there are likely to be more tornadoes than normal across the United States.

Climate change is indirectly related to this forecast because strong thunderstorms create conditions where tornadoes can form, and strong thunderstorms could be fueled by the warmer-than-normal surface waters of the Gulf of Mexico, according to Paul Walker, senior meteorologist at Accuweather.

Tornadoes caused $28.7 billion in damage in the United States in 2011, and killed more than 550 people, the U.S. National Climatic Data Center found.

One reason the loss of life and financial toll were so high last year was because some of the most severe tornadoes hit populated areas, notably Joplin, Missouri, and Birmingham, Alabama, Walker said.

This may have been caused by a strong La Nina pattern, which can shift "Tornado Alley" eastward from its normal span in the plains of Kansas, Oklahoma and Texas.

La Nina starts as a cool patch of water in the equatorial Pacific that can have a global weather impact; El Nino is a warm swathe of water in the same area. There is little sign of a strong La Nina or El Nino this year, Accuweather said.

Total U.S. damage in 2011 from climate and weather disasters, including drought, was $55 billion. Floods along the Mississippi and the upper Midwest cost an estimated $5 billion damage and claimed at least 12 lives, according to the National Climatic Data Center.

If taken as a single event, last year's spring tornado season would have been the fourth-costliest disaster in U.S. history from an insurance perspective, behind hurricanes Katrina and Andrew and the Sept. 11, 2001, attacks on the United States.

A new study suggests climate change could cause more flooding as storm surges - the damaging masses of water propelled inland by hurricanes and other storms - become more frequent.

Floods that have been expected once a century could happen every three to 20 years, researchers from Princeton University and the Massachusetts Institute of Technology reported in the latest issue of Nature Climate Change.

Such sharp changes in climate could force insurers to reconsider the losses they face. If such one-in-100-years storms start occurring every 20 years or less, it may lead insurers to reduce their exposure to certain regions or charge substantially more for coverage. (Additional reporting by Ben Berkowitz; Editing by Vicki Allen)

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