In hydrology, applied to a natural watercourse which responds rapidly to a storm event, hence flash flood; a very sudden, brief, and dramatic flood event—rising and falling limbs are steep, and the period of peak flow is short. Flash floods are major hazards in deserts, for, although rainfall is rare, the hard-baked ground may be impermeable, and there is little or no vegetation to intercept the rainfall or slow the floodwater. For the prediction of flash floods, see Mukhopadhyay et al. (2003) Hydrol. Procs 17, 4 and Foody (2004) J. Hydrol. 292, 1–4. Flash flooding is the major process in the formation of wadis—which, incidentally, should therefore be avoided as camp sites. See Chhopel (2006) Procs Int. Workshop Flash Flood Forecasting on flash floods and glacial lake outbursts, and Chan (1997) Disaster Prevention & Management 6, 2 on urbanization and flash flooding in Kuala Lumpur; see also Gupta in O. Hassan et al., eds (2000).

http://pubs.usgs.gov/fs/fs117-03/ USGS description and depiction of effects of flash flooding precipitation on desert geomorphology during El Niño years.