In the USA, there are two main types of flooding: flash floods and river floods. Flash floods generally cause loss of life, and river floods generally cause loss of property.
- Flash flood occurs when runoff from excessive rainfall causes a rapid rise in the water height (stage) of a stream or normally-dry channel. Flash floods are more common in areas with a dry climate and rocky terrain because lack of soil or vegetation allows torrential rains to flow overland rather than infiltrate into the ground.
- River flooding is generally more common for larger rivers in areas with a wetter climate when excessive runoff from longer-lasting rainstorms and sometimes from melting snow causes a slower water-level rise over a larger area.