WASHINGTON (By Deborah Zabarenko) - Heavy rains, deep snowfalls, monster floods and killing droughts are signs of a "new normal" of extreme U.S. weather events fueled by climate change, scientists and government planners said on Wednesday.

"It's a new normal and I really do think that global weirding is the best way to describe what we're seeing," climate scientist Katharine Hayhoe of Texas Tech University told reporters.

"We are used to certain conditions and there's a lot going on these days that is not what we're used to, that is outside our current frame of reference," Hayhoe said on a conference call with other experts, organized by the non-profit Union of Concerned Scientists.

An upsurge in heavy rainstorms in the United States has coincided with prolonged drought, sometimes in the same location, she said, noting that west Texas has seen a record-length dry period over the last five years, even as there have been two 100-year rain events.

Hayhoe, other scientists, civic planners and a manager at the giant Swiss Re reinsurance firm all cited human-caused climate change as an factor pushing this shift toward more extreme weather.

While none would blame climate change for any specific weather event, Hayhoe said a background of climate change had an impact on every rainstorm, heat wave or cold snap.

"What we're seeing is the new normal is constantly evolving," said Nikhil da Victoria Lobo of Swiss Re's Global Partnerships team. "Globally what we're seeing is more volatility ... there's certainly a lot more integrated risk exposure."

CHICAGO'S SEWERS

In addition to more extreme local weather events, he said, changes in demographics and how materials are supplied make them more vulnerable.

"In a more integrated economic system, a single shock to an isolated area can actually end up having broad-based and material implications," da Victoria Lobo said. For example, if a local storm knocks out transport and communications systems, "someone 1,000 miles away is not receiving their iPad or their car."

Aaron Durnbaugh, deputy commissioner for natural resources and water quality for Chicago, said adapting to climate change is a daunting task.

Citing the down-to-earth example of Chicago's 4,400 miles of sewer mains, which were installed over the last 150 years and will take decades to replace, Durnbaugh said accurate forecasting of future storms and floods is essential.

The city of Chicago's cost of dealing with extreme weather events through the end of this century has been conservatively estimated in a range from $690 million to $2.5 billion, Durnbaugh said, with the cost to homeowners and local businesses expected to be far higher.

Globally, da Victoria Lobo said the annual average economic losses from natural disasters have escalated from $25 billion in the 1980s to $130 billion in the first decade of the 21st century.

(Editing by Eric Walsh)

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