What is a "flash flood"?

A flash flood is characterized by a rapid onset of flooding, typically occurring within six hours of heavy rainfall or sudden water runoff, often in low-lying areas. This type of flooding can result from intense rainfall over a short duration, rapid melting of snow, or sudden release of water from dams or reservoirs. Because the flooding can escalate very quickly, it poses a significant risk to life and property, necessitating prompt warnings and responses.

While extended periods of heavy rainfall can contribute to flooding, such conditions generally lead to a slower rise in water levels, which is characteristic of more gradual flooding scenarios rather than the immediate danger that flash floods present. Similarly, slow-rising waters from a river refer to a different phenomenon where water levels increase steadily, providing more time for individuals to prepare. Tidal waves, or tsunamis, involve large ocean waves typically caused by seismic activity and do not relate to the rapid, localized impacts associated with flash flooding. Thus, the emphasis on the rapidity and the specific context of low-lying areas makes the definition of a flash flood distinct and clear.