BOULDER -- Societal changes, much more than increased precipitation,spurred a steep rise in flood-damage costs in the United States overmuch of the past century, according to a new study published October15 in the Journal of Climate. U.S. annual flood losses, adjusted forinflation, rose from $1 billion in the 1940s to $5 billion in the1990s.
"Climate plays an important but by no means determining role in thegrowth of damaging floods in the United States in recent decades,"write the authors, Roger Pielke Jr. and Mary Downton, both of theNational Center for Atmospheric Research. NCAR's primary sponsor isthe National Science Foundation.
Pielke and Downton examined ten different measures of precipitation.They found a strong relationship between flood damage and the numberof two-day heavy rainfall events and wet days. They also found asomewhat weaker relationship between flood damage and two-inchrainfall events in most regions. However, these relationships couldnot explain the dramatic growth in flood losses, according to theauthors.
In a series of recent articles, including this one in the Journal ofClimate, Pielke, Downton, and colleagues looked at the role ofincreasing precipitation, population, and national wealth. They foundthat population growth alone accounts for 43% of the rise in flooddamages from 1932 to 1997, with a much smaller effect from increasedprecipitation. "Most of the other 57% increase is due to burgeoningnational wealth," says Pielke. Downton's work suggests that moredetailed disaster reporting also contributes to the trend.
Climate scientists have observed a rise in precipitation in someareas of the United States and elsewhere over the past century. TheIntergovernmental Panel on Climate Change (IPCC) has written that awarmer climate could lead to more heavy-rain events. The Pielke-Downton paper found that flooding increases with precipitation,depending greatly on the time and location of the rain or snowfall.However, "even without an increase in precipitation," they write,"total flood damage will continue to rise with the nation's growingpopulation and wealth unless actions are taken to reducevulnerability."
Pielke, a political scientist, has often stated that his work "isconsistent with the conclusions of the IPCC," whose consensus view isthat the earth's climate is changing at least partly because of humanactivity. "But," he argues, "debate over the science of globalwarming need not stand in the way of effective actions to betteraddress climate impacts."
"We know enough to act now," said Pielke in a recent presentation atNCAR. "We can manage spiraling flood costs without waiting forprecise answers from climate change research. In this sense thedebate over global warming misses the mark." Disaster mitigationpolicies regarding floodplain management are already in place andcan curtail the rising costs, he said.
Globally, between 1970 and 1995 floods killed more than 318,000people and left more than 81 million homeless. During 1991-95 floodrelated damage totaled more than $200 billion worldwide, representingclose to 40% of all economic damage attributed to natural disastersin that period.
NCAR is managed by the University Corporation for AtmosphericResearch, a consortium of more than 60 universities offering Ph.D.sin atmospheric and related sciences.
Materials provided by National Center For Atmospheric Research (NCAR). Note: Content may be edited for style and length.
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