Floods

A flood is an overflow of water that submerges normally dry land. The floods included in this analysis caused personal injury or loss of life, property damage, and/or disruption to commerce or transportation.


Aaron Baker

May 7, 2021 • Updated Mar 17, 2022 • 4 min read

Find floods and other environmental hazards near you here

Flooding is the most widespread of all weather-related natural disasters. Floods are dangerous, cause significant property damage, may reduce property values, and are becoming more frequent in some areas.

Overview#

Flooding occurs when water overflows onto land that is normally dry. It happens during heavy rains, when ocean waves come onshore, when snow melts quickly, and when dams or levees break. Floods are the most common and widespread of all weather-related natural disastersand include river floods, flash floods, and coastal floods. Flooding can occur within a few minutes or over longer periods and can last for weeks or longer.

River floods normally result from excessive rain, rain combined with snowmelt, or an ice jam. In some areas, the soil is unable to absorb heavy rainfall and flash floods develop. Land use practices that remove vegetation and decrease the ability of soil to absorb water can contribute to river floods. For example, in 2019, the Mississippi River remained above flood stage in many locations for over six months as a result of excessive rainfall combined with snowmelt and a history of land management that has reduced the ability of the surrounding landscape to absorb water.

Flash floods are the most dangerous type of flood because they combine the destructive power of a flood with incredible speed and little or no warning. Most flood-related deaths in the US are attributed to flash floods. They are typically raging torrents of water in river beds, city streets, or canyons. Deforestation and urbanization both reduce the ability of soil to absorb water and can contribute to flash floods. Failed levees or dams or a sudden release of water from an ice or debris jam can also cause flash floods.

Coastal flooding occurs as a result of higher than normal high tides and is worsened by rainfall, snowmelt, or onshore winds. Along the Atlantic and Gulf coasts this type of flooding can be common--for example, Savannah, Georgia and Charleston, South Carolina both experience this type of shallow coastal flooding several times a year. The frequency of coastal flooding is increasing--NOAA researchers predict that the number of coastal floods will continue to increase and may double by 2030 and be 5-15 times more common by 2050. Storm surge is water that is pushed towards shore by winds and often occurs during hurricanes. Storm surge combined with a normal high tide can produce water levels 15 feet above a normal high tide and flood as much as 30 miles inland from the coast.

Your Home and Floods#

Health and Safety#

The National Weather Service (NWS) issues a variety of flood-related advisories and warnings. These can be monitored directly through the NWS or your local radio or television stations. The NWS has developed clear guidelines for what to do before, during, and after a flood. These include preparing in advance by assembling an emergency kit, knowing your risk, signing up for NWS notifications of alerts via text message, preparing your family and pets, and charging essential electronics. During a flood stay informed, get to higher ground, obey evacuation orders, practice electrical safety, and avoid floodwaters. After a flood, avoid floodwaters and disaster areas, heed road closed and cautionary signs, and wait for the All Clear by authorities before entering flood-damaged homes or buildings.

Property Values#

Flooding causes an average of $5 billion in damage each year in the US--more than any other severe weather-related event. In general, property values are negatively impacted by a flood zone designation as well as actual flooding. A study in the Fargo-Moorhead Metropolitan area of North Dakota found that home values within a 100-year floodplain typically had a market value of 3.5-12.2% lower than similar homes located outside of the floodplain. Research on property values in Miami-Dade County in Florida estimated that properties at risk of recurrent tidal flooding go down in value over $3 per square foot annually. In addition, a single major flooding event can also reduce property values--following Hurricane Sandy, undamaged properties in designated flood zones in New York City decreased in value by over 8%.

What You Can Do#

Most homeowners insurance does not cover flood damage. If your home is in a high-risk flood zone, then flood insurance is required if you have a mortgage with a government-backed lender and can be purchased at a subsidized rate through FEMA’s National Flood Insurance Program (NFIP). Discounts are also available on flood insurance through NFIP by retrofitting your home to mitigate risk from flooding. Flood insurance is also available regardless of flood zone designation from private carriers outside of the NFIP.

AreaHub’s Knowledge Center is updated regularly and provides information drawing upon scientific studies and sources.

Sources#