Flash Flood Warning

Flash floods are one of the most devastating types of natural hazards. The main threat arises from the speed with which they develop and the depth and power of the resulting flows. Similar risks arise from related phenomena such as debris flows, ice jams and surface water flooding, often called stormwater or pluvial flooding. Perhaps the most comprehensive way to provide early warnings is to install gauges both at and upstream of areas at risk and to use forecasts from ensemble meteorological, hydrological and hydrodynamic models to help to extend warning lead times. However, often this is not feasible so other options include heavy rainfall warnings and flash flood guidance techniques. This chapter provides an introduction to these topics and discusses how the accuracy of warnings and the time available for response can be increased through improvements throughout the monitoring, forecasting and warning chain. Community early warning systems often play an important role in this process. Specialised types of instrumentation and early warning techniques are also discussed for debris flows, ice jams and surface water floods.