| Flash floods - rapid rises in water levels | | | | quickly absorb the water and the lack of |
| with high flow velocities - can occur in a | | | | plant life to slow the water's course. |
| matter of seconds. Factors such as rainfall | | | | |
| intensity and duration, as well as regional | | | | Areas with a high risk of flash floods (such |
| topography, can all contribute to a flash | | | | as the land surrounding large dams) often |
| flood situation. Urbanization is also an | | | | have warning systems in place to help alert |
| important cause of flash floods. The roofs, | | | | the population in advance of a flood. The |
| sidewalks, and roads of a city create | | | | forecast center for your region calculates |
| dangerous amounts of runoff water during big | | | | flash flood guidance for all the bodies of |
| storms, and this runoff can easily become a | | | | water in the area. Flash flood guidance is |
| flash flood if an adequate storm sewer system | | | | the amount of rainfall for a given duration |
| is not in place. | | | | necessary to produce flash flooding. With |
| | | | these figures readily available, weather |
| In mountainous regions the rainfall can run | | | | services can provide predictions and early |
| down a steep mountain and pick up so much | | | | warnings to give inhabitants of the region |
| speed that it becomes a dangerous wave moving | | | | time to move to higher ground. |
| too fast for people to escape. A similar | | | | |
| situation occurred in Rapid City, South | | | | If you live in a region that is prone to |
| Dakota, in 1972 when 237 people were killed. | | | | flash floods, make sure you have a map to the |
| | | | quickest region of high ground. Also, make |
| Even deserts are not immune to flash | | | | sure you monitor weather service |
| flooding. Dry riverbeds can channel water | | | | announcements during big storms in case of a |
| long distances and create dangerous flood | | | | flash flood warning. |
| waves, due to the ground being too dry to | | | | |