8/6/2019 48725-Common Causes of Flooding Fact Sheet

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FACT SHEET

February 2011

Flooding Our Nations Most Frequent and Costly Natural Disaster

HISTORY AND CAUSES

FLOOD SAFETY AWARENESS

FEMA and the National Flood Insurance Program

(NFIP) are proud to partner with the National

Oceanic and Atmospheric Administration (NOAA)and National Weather Service (NWS) to demonstrate

flood risks across the country and provide important

information about steps you can take to protectyourself and your family.

HISTORY OF FLOODING

FLOODING is the most frequent severe weatherthreat and the costliest natural disaster facing thenation. Ninety percent of all natural disasters in theU.S. involve flooding. And high-risk flood areas arenot the only ones at risk: more than 20% of all floodinsurance claims come from policies in moderate-to low-risk areas.

CAUSES OF FLOODING

SPRING THAW

During the spring, frozen land prevents meltingsnow or rainfall from seeping into the ground.When the snow does melt, it can overflow streams,rivers and lakes. Add spring storms, and the result isoften severe spring flooding. In spring 2009, Alaskaexperienced record-breaking flooding after warmer-than-normal temperatures caused snowmelt and icejams along Alaskan rivers. The resulting damage tohomes, roads and airports was estimated at morethan $7.2 million.

HURRICANES

Hurricanes can bring strong winds, heavy rains andstorm surge in coastal areas. As hurricanes and

tropical storms move inland, torrential rains andhigh winds can cause damage hundreds of milesfrom the coast. Hurricane Ike in 2008 was the thirdmost destructive hurricane ever to hit the UnitedStates. In Texas, Ikes 100 mph winds, 13-foot highstorm surge and 16 inches of rain destroyedthousands of homes and properties. Figures fromNOAAs National Climatic Data Center reports putslosses from the storm at $27 billion.

TROPICAL STORMS

Wind speeds dont tell the entire story when itcomes to tropical storms. Intense rainfall, notdirectly related to the wind speed of a tropicalstorm, often causes the most damage. In November2009, remnants of Tropical Storm Ida redevelopedinto a strong coastal storm (noreaster) thatgenerated up to 18 inches of rain in many areas andcaused major flooding along the Atlantic Coast. The

storm caused an estimated $70 million in damage inVirginia alone.

HEAVY RAINS

All areas of the country are at heightened risk forflooding due to heavy rains. This excessive rainfallcan happen during any season, putting property atrisk year round. In April and May 2010, heavy rainand severe storms battered many Southern states,including Tennessee, Arkansas, Alabama,Kentucky, Mississippi, and Georgia. Western andmid-Tennessee were hardest hit with local rainfallamounts of 18-20 inches to the south and west ofthe Nashville metropolitan area. Flooding in theNashville, Tennessee area alone caused more than$1 billion in damages.

8/6/2019 48725-Common Causes of Flooding Fact Sheet

2/2

FACT SHEET

February 2011

Flooding Our Nations Most Frequent and Costly Natural Disaster

HISTORY AND CAUSES

WEST COAST THREATS

The West Coast rainy season usually lasts fromNovember to April, bringing the majority of yearlyprecipitation to states in the Pacific Northwest. InJanuary 2009, Washington experienced some of theworst flooding on record. A combination of heavyrains and snowmelt caused extensive flooding andmudslides, with an estimated $125 million in flooddamage to roads, buildings and other government

structures

LEVEES & DAMS

The U.S. has thousands of miles of levees and damsthat are designed to protect against a certain level offlooding. These structures can erode and weakenover time, and they can also be overtoppedoreven failduring large flood events. Heavy rains inJuly caused the Lake Delhi dam in Iowa to burst,emptying a nine mile lake and leading to

catastrophic flooding.

FLASH FLOODS

Flash flooding is the #1 weather-related killer in theU.S. A flash flood is a phenomenon such as athunderstorm, collapse of a man-made structure oran ice break that occurs within six hours of an eventand generates significant flood waters. In March2010, flash floods occurred throughout Virginia andWest Virginia as a result of snowmelt compiledwith moderate to heavy rain. This event was

categorized as the most high-impact flash flood toaffect the Blacksburg area in the past five yearswith preliminary damages estimated at least $6million.

To learn what you can do to prepare for floods, visitwww.ready.gov/floodawareness .

Visit www.floodsmart.gov to learn more about floodcauses, safety precautions, flood risks, and floodinsurance policy options.

http://www.ready.gov/floodawarenesshttp://www.floodsmart.gov/http://www.floodsmart.gov/http://www.ready.gov/floodawareness