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Climate change blamed for a third of U.S. flood losses in past 3 decades

(Thomson Reuters Foundation) - Climate change has boosted the cost of flood damage caused by heavy rainfall in the United States by $75 billion over the last three decades, accounting for about a third of total losses, Stanford University researchers said on Monday.

With planet-heating emissions still going up, both extreme rainfall and related losses will continue to grow, they said - though strong efforts to curb emissions and adapt to changing conditions could help hold the line.

“The more global warming we get, the more we can expect these damages to increase - and reductions (in emissions) will have value in terms of avoided costs,” said climate scientist Noah Diffenbaugh, co-author of a new study published in the Proceedings of the National Academy of Sciences.

Total U.S. flood costs from heavy rainfall between 1988 and 2017 are estimated at $199 billion, and the losses have surged as climate warming speeds up the planet’s water cycle, driving more extreme precipitation.

Flooding is the most common weather-related disaster threat in the United States.

Researchers, however, have long struggled to determine how much of the rising costs are due to additional housing development to serve a growing population, as well as increases in property values.

The Stanford University team developed a model to analyse changes in these economic indicators and to extract them, in order to clarify the role of climate change.

The model developed could similarly be used to calculate the contribution of climate change to wildfire losses or reductions in crop yields from rising temperatures, if long-term data records are available, Diffenbaugh said.

Evidence that global warming is already driving more than a third of U.S. flood losses from heavy rainfall - the study did not look at flooding related to sea level rise - should push governments to step up emissions reductions and prepare for flood risks, he said.

“Decisions about what to do about climate change, how aggressively to curb greenhouse gas emissions as outlined in the Paris Agreement, or decisions on how to invest in adaptation - those are cost-benefit decisions,” Diffenbaugh said.

Quantifying the fraction of historical costs contributed by climate change provides real numbers to evaluate those cost-benefit decisions, he told the Thomson Reuters Foundation.

Researchers said most of the growing climate-linked losses were not being driven by overall increases in rainfall but by hikes in extreme rainfall events.

“What we find is that, even in states where the long-term mean precipitation hasn’t changed, in most cases the wettest events have intensified,” said Frances Davenport, an Earth system science graduate student and co-author of the study.

That is increasing the financial damages relative to what would have occurred without the precipitation shifts, she said.

Besides curbing global warming, efforts to avoid building new homes on vulnerable floodplains could also limit losses, as the two go hand-in-hand, she added.

Environmental and planning groups last week petitioned the Federal Emergency Management Agency (FEMA) to update its flood maps, set tougher standards for floodplain construction and prepare for climate change.

FEMA rules on floodplain use have not been comprehensively revised since the 1970s, meaning homes are still being built in areas likely to flood as global warming brings higher seas and more extreme rainfall and storms, the groups said.

Reporting by Laurie Goering @lauriegoering; editing by Megan Rowling. Please credit the Thomson Reuters Foundation, the charitable arm of Thomson Reuters. Visit news.trust.org/climate

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