Oct. 20, 2000 BOULDER -- Societal changes, much more than increased precipitation, spurred a steep rise in flood-damage costs in the United States over much of the past century, according to a new study published October 15 in the Journal of Climate. U.S. annual flood losses, adjusted for inflation, rose from $1 billion in the 1940s to $5 billion in the 1990s.
"Climate plays an important but by no means determining role in the growth of damaging floods in the United States in recent decades," write the authors, Roger Pielke Jr. and Mary Downton, both of the National Center for Atmospheric Research. NCAR's primary sponsor is the National Science Foundation.
Pielke and Downton examined ten different measures of precipitation. They found a strong relationship between flood damage and the number of two-day heavy rainfall events and wet days. They also found a somewhat weaker relationship between flood damage and two-inch rainfall events in most regions. However, these relationships could not explain the dramatic growth in flood losses, according to the authors.
In a series of recent articles, including this one in the Journal of Climate, Pielke, Downton, and colleagues looked at the role of increasing precipitation, population, and national wealth. They found that population growth alone accounts for 43% of the rise in flood damages from 1932 to 1997, with a much smaller effect from increased precipitation. "Most of the other 57% increase is due to burgeoning national wealth," says Pielke. Downton's work suggests that more detailed disaster reporting also contributes to the trend.
Climate scientists have observed a rise in precipitation in some areas of the United States and elsewhere over the past century. The Intergovernmental Panel on Climate Change (IPCC) has written that a warmer 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 growing population and wealth unless actions are taken to reduce vulnerability."
Pielke, a political scientist, has often stated that his work "is consistent with the conclusions of the IPCC," whose consensus view is that the earth's climate is changing at least partly because of human activity. "But," he argues, "debate over the science of global warming need not stand in the way of effective actions to better address climate impacts."
"We know enough to act now," said Pielke in a recent presentation at NCAR. "We can manage spiraling flood costs without waiting for precise answers from climate change research. In this sense the debate over global warming misses the mark." Disaster mitigation policies regarding floodplain management are already in place and can curtail the rising costs, he said.
Globally, between 1970 and 1995 floods killed more than 318,000 people and left more than 81 million homeless. During 1991-95 flood related damage totaled more than $200 billion worldwide, representing close to 40% of all economic damage attributed to natural disasters in that period.
NCAR is managed by the University Corporation for Atmospheric Research, a consortium of more than 60 universities offering Ph.D.s in atmospheric and related sciences.
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