Floods and Droughts

Floods are a dangerous hazard throughout the world. On average in the United States, about 165 people are killed and about $2 billion of damage occurs each year. Most people underestimate the power and destructiveness of flood waters.
Most currently available flood maps are used to assist planners in identifying and preparing for flooding scenarios. These maps portray statistics based on long-term historical records to estimate and forecast an approaching weather system.
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.
Several types of data can be collected to assist hydrologists predict when and where floods might occur:
Several kinds of flood maps are available from USGS and other sources.Online USGS map showing real-time flood conditions
A drought is a period of drier-than-normal conditions that results in water-related problems. Precipitation (either rain or snow) falls in uneven patterns across the country.
The beginning of a drought is difficult to determine. Several weeks, months, or even years may pass before people know that a drought is occurring. The end of a drought can occur as gradually as it began. Dry periods can last for 10 years or more.
A period of below-normal rainfall does not necessarily result in drought conditions. Some rain returns to the air as water vapor when water evaporates from water surfaces and from moist soil.
Rainfall in any form will provide some drought relief. A good analogy might be how medicine and illness relate to each other.