Flash floods rapid rises in water levels with high flow velocities can occur in a matter of seconds. Factors such as rainfall intensity and duration, as well as regional topography, can all contribute to a flash flood situation. Urbanization is also an important cause of flash floods. The roofs, sidewalks, and roads of a city create dangerous amounts of runoff water during big storms, and this runoff can easily become a flash flood if an adequate storm sewer system is not in place.

In mountainous regions the rainfall can run down a steep mountain and pick up so much speed that it becomes a dangerous wave moving too fast for people to escape. A similar situation occurred in Rapid City, South Dakota, in 1972 when 237 people were killed.

Even deserts are not immune to flash flooding. Dry riverbeds can channel water long distances and create dangerous flood waves, due to the ground being too dry to quickly absorb the water and the lack of plant life to slow the waters course.

Areas with a high risk of flash floods (such as the land surrounding large dams) often have warning systems in place to help alert the population in advance of a flood. The forecast center for your region calculates flash flood guidance for all the bodies of water in the area. Flash flood guidance is the amount of rainfall for a given duration necessary to produce flash flooding. With these figures readily available, weather services can provide predictions and early warnings to give inhabitants of the region time to move to higher ground.

If you live in a region that is prone to flash floods, make sure you have a map to the quickest region of high ground. Also, make sure you monitor weather service announcements during big storms in case of a flash flood warning.