Understanding Damage and Impacts
Why does flooding cause so many deaths?
Flooding is the most common of all natural hazards. Each year, more deaths are caused by flooding than any other thunderstorm related hazard. We think this is because people tend to underestimate the force and power of water. Six inches of fast-moving water can knock you off your feet. Water 24 inches deep can carry away most automobiles. Nearly half of all flash flood deaths occur in automobiles as they are swept downstream. Most of these deaths take place when people drive into flooded highway dips of low drainage areas. The NWS has a program called "Turn around don't drown!" to educate the public about these dangers.
Though the numbers can vary dramatically from year to year, the 30-year national
average for flood deaths is 127. The 30-year average for lightning is 73 deaths,
compared with 65 for tornadoes, and 16 for hurricanes. We do know that flooding
has caused the deaths of more than 10,000 people since 1900.
Many of the 1300 deaths during Hurricane Katrina in 2005 were a direct result of urban flooding caused by levee failures, and coastal storm surge caused by the massive hurricane itself. Many lives were needlessly lost because people at all levels of government and private citizens underestimated the danger and did not react quickly enough to timely warnings.
What kinds of damage can flash floods do?
Flash floods can roll boulders, tear out trees, destroy buildings, and obliterate bridges. Walls of water can reach heights of 10 to 20 feet and generally are accompanied by a deadly cargo of debris.
What are some economic impacts of flash floods?
Photo by Leif Skoogfors/ FEMA
On average, flooding causes more than $2 billion in damage to property each year. A significant part of the preliminary estimate of over $100 billion in damage/costs resulting from Hurricane Katrina is the damage from flooding in New Orleans.
In another notable flood event, the central U.S. experienced severe, widespread flooding over parts of nine states for three months during the the summer of 1993 due to persistent heavy rains and thunderstorms, costing approximately $21.0 billion and causing 48 deaths.
HOW DOES NSSL CONTRIBUTE?
NSSL is working hard to improve warnings and forecasts of flash floods. By investigating the meteorological causes of flash flooding and working on flash flood and river flood warning decision making tools, we hope to see more lives saved.
Debris Flow – California is particularly susceptible to mudslides and debris flow caused by extreme rainfall. Homes are frequently destroyed and major highways and commuting routes can be washed out. Two NSSL researchers were invited by the NWS to serve on an interagency team to create a debris flow, or mudslide warning system for southern California. The interagency team will provide guidelines for the warning system including developing a research plan for improved QPE over the southern California mountains.