Still, you can take steps to prepare for these types of emergencies. A flash flood watch is issued when flash flooding is possible within the designated watch area - be alert. A flash flood warning is issued when a flash flood has been reported or is imminent - take necessary precautions. On small streams, especially near the headwaters of river basins, water levels may rise quickly in heavy rainstorms, and flash floods can begin before the rain stops falling. There is little time between detection of flood conditions and the arrival of the flood crest.
Swift action is essential to protect life and property.
Flash floods also occur in or near mountainous area where torrential thunderstorm rains can quickly change a dry water curse or trickling little brook into raging treacherous torrents of water. Desert washes, particularly near mountains, can go from dry to flood stage within minutes as a result of thundershowers many miles away and out of sight or hearing of the flash flood site. Urban flooding can occur in any terrain and is particularly aggravated by urbanization where natural cover has been removed by the construction of buildings, roads and parking lots. Heavy rains can result in flash flooding, inundating cars and causing considerable damage to residential and industrial properties located along the stream channels. Flash Floods Flash flood waves, moving at incredible speeds, can roll boulders, tear out trees, destroy buildings and bridges, and scour out new channels.