More Than One-Third of U.S. Facing High Risk of Flooding

March 17, 2010

Major flooding has begun and is forecast to continue through spring in parts of the Midwest, according to the National Weather Service. The South and East are also more susceptible to flooding as an El Niño influenced winter has left the area soggier than usual.

Overall, more than a third of the contiguous United States has an above average flood risk –– with the highest threat in the Dakotas, Minnesota and Iowa, including along the Red River Valley where crests could approach the record levels set just last year.

Supporting the forecast of imminent Midwest flooding is a snowpack more extensive than in 2009 and containing in excess of 10 inches of liquid water in some locations. Until early March, consistently cold temperatures limited snow melt and runoff. These conditions exist on top of: above normal streamflows; December precipitation that was up to four times above average; and the ground which is frozen to a depth as much as three feet below the surface.

“It’s a terrible case of déjà vu, but this time the flooding will likely be more widespread. As the spring thaw melts the snowpack, saturated and frozen ground in the Midwest will exacerbate the flooding of the flat terrain and feed rising rivers and streams,” said Jane Lubchenco, Ph.D., under secretary of commerce for oceans and atmosphere and NOAA administrator. “We will continue to refine forecasts to account for additional precipitation and rising temperatures, which affect the rate and severity of flooding.”

In the South and East, where an El Niño-driven winter was very wet and white, spring flooding is “more of a possibility than a certainty and will largely be dependent upon the severity and duration of additional precipitation and how fast existing snow cover melts,” said Jack Hayes, Ph.D., director of the National Weather Service. “Though El Niño is forecast to continue at least through spring, its influence on day-to-day weather should lessen considerably.”

Without a strong El Niño influence, climate forecasting for spring (April through June) is more challenging, but the Climate Prediction Center of the National Oceanic and Atmospheric Administration (NOAA) says odds currently favor wetter-than-average conditions in coastal sections of the Southeast; warmer-than-average temperatures across the western third of the nation and Alaska; and below-average temperatures in the extreme north-central and south-central U.S.

This is national Flood Safety Awareness Week. Floods are the deadliest weather phenomena — claiming an average of 100 lives annually.

Source: NOAA National Weather Service

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