El Nino is so named because the effects of the warmer water off Peru is usually noticed near Christmas time. Several types of data can be collected to assist hydrologists predict when and where floods might occur. Second, monitoring the rate of change in river stage on a realtime basis can help indicate the severity and immediacy of the threat. Third, knowledge about the type of storm producing the moisture, such as duration, intensity, areal extent, etc., is valuable for determining possible severity of the flooding. And fourth, knowledge about the characteristics of a river's drainage basin, such as soil-moisture conditions, ground temperature, snowpack, topography, vegetation cover, impermeable land area, etc., can help to predict how extensive and damaging an impending flood might become.
Floods are a dangerous hazard throughout the world.
Most people underestimate the power and destructiveness of flood waters. There are two basic kinds of floods, flash floods and the more widespread river flooding. Flash floods generally cause greater loss of life and river floods generally cause greater loss of property. A flash flood occurs when runoff from excessive rainfall causes a rapid rise in the stage of a stream or normally dry channel. Floods also can be caused by ice jams on a river, or high tides.