How are floods predicted?
Several types of data can be collected to assist hydrologists predict when and where floods might occur:
- Monitoring the amount of rainfall occurring on a realtime basis
- Monitoring the rate of change in river stage on a realtime basis, which can help indicate the severity and immediacy of the threat
- Knowledge about the type of storm producing the moisture, such as duration, intensity and areal extent, which can be valuable for determining possible severity of the flooding
- Knowledge about the characteristics of a river's drainage basin, such as soil-moisture conditions, ground temperature, snowpack, topography, vegetation cover, and impermeable land area, which can help to predict how extensive and damaging a flood might become
The National Weather Service collects and interprets rainfall data throughout the United States and issues flood watches and warnings as appropriate. The National Weather Service uses statistical models and flood histories to try to predict the results of expected storms. The USGS maintains a network of streamflow-gaging stations throughout the country for which the discharge and stage are monitored. Flood estimation maps are generally produced by estimating a flood with a certain recurrence interval or probability and simulating the inundation levels based on flood plain and channel characteristics.