FLASH FLOODS - The #1 Weather Related Killer in the United States!
Courtesy of National Weather Service Phoenix
How do flash floods occur?
Several factors contribute to flash flooding. The two key elements are rainfall intensity and duration. Intensity is the rate of rainfall, and duration is how long the rain lasts. Topography, soil conditions, and ground cover also play important roles.
Flash floods occur within a few minutes or hours of excessive rainfall, a dam or levee failure, or a sudden release of water held by an ice jam. Flash floods can roll boulders, tear out trees, destroy buildings and bridges, and scour out new channels. Rapidly rising water can reach heights of 30 feet or more. Furthermore, flash-flood producing rains can trigger catastrophic mud slides. You will not always have a warning that these deadly, sudden floods are coming.
Most flood deaths are due to FLASH FLOODS.
FLASH FLOODS / FLOODS:
- Are the #1 cause of deaths associated with thunderstorms...more than 140 fatalities each year
- Most flash flood deaths occur at night...and most victims are trapped in cars
- Six inches of fast-moving water can knock you off your feet - a depth of two feet will cause most vehicles to float!
- * photo by Warren Faidley, Weatherstock
Look out for WATER RISING RAPIDLY!
Nearly HALF of all flash flood deaths are auto-related
In your car, look out for...
- flooding at highway dips, bridges and low areas
- many flash floods occur at night...be prepared to take quick action!
FLASH FLOODING TAKES MULTIPLE FORMS
- URBAN FLOOD - As land is converted from fields, woodlands or deserts to roads and parking lots, it loses its ability to absorb rainfall. Urbanization increases runoff 2 to 6 times over what would occur on natural terrain. During periods of urban flooding, streets can become swiftly moving rivers, while basements can become death traps as they fill with water.
- FLASH FLOODING IN ARROYOS/WASHES - An arroyo is a water-carved gully or normally dry creek bed. Arroyos can fill with fast-moving water very quickly. Flash flooding at some arroyos can take less than one minute to develop!
- ICE JAM - Floating ice can accumulate at a natural or man-made obstruction and stop the flow of water. When the obstruction is quickly released, flash flooding can occur.
Stay informed about the storm by listening to NOAA Weather Radio, commercial radio and television for the latest flash flood watches, warnings and advisories! NOAA Weather Radio is the best means to receive warnings from the National Weather Service.
WHAT TO LISTEN FOR...
- FLASH FLOOD WATCH: Flash flooding is possible within the designated watch area - BE ALERT!
- FLASH FLOOD WARNING: Flash flooding has been reported or is imminent - take necessary precatuions at once.
- URBAN AND SMALL STREAM FLOOD ADVISORY: Flooding of small streams, streets, and low-lying areas such as railroad underpasses and urban storm drains, is occurring.
- FLOOD STATEMENT: Follow up information regarding a flash flood event.
FLASH FLOOD SAFETY RULES
- When a flash flood WATCH is issued...be alert to signs of flash flooding and be prepared to evacuate on a moment's notice
- When a flash flood WARNING is issued for your area, or the moment you realize that a flash flood is imminent, act quickly to save yourself. YOU MAY HAVE ONLY SECONDS!
- GO TO HIGHER GROUND - CLIMB TO SAFETY
- Get out of areas subject to flooding. This includes dips, low spots, canyons, washes, etc.
- Avoid already flooded and high velocity flow areas. Do NOT attempt to cross flowing streams.
- If driving, be aware that the road bed may not be intact under flood waters. Turn around and go another way. DO NOT drive through flooded roadways! The road bed may be washed out under the water and you could be stranded or trapped.
- If the vehicle stalls, leave it immediately and seek higher ground. Rapidly rising water may engulf the vehicle and its occupants and sweep them away. Remember, it's better to be WET than DEAD!
- Be especially cautious at night when it is harder to recognize flood dangers.
- Do not camp or park your vehicle along streams and washes, particularly during threatening weather conditions.
- Children should NEVER play around high water, storm drains, viaducts or arroyos.
• If you come upon a flowing stream where the water is above your ankles, STOP! Turn around and go another way. If water is moving swiftly, even water six inches deep can knock you off your feet.