Floods occur when a normally drier land area is temporarily submerged in water overflowing from rivers, dams (barrier to contain the flow of water), runoff, or tides. Runoff is water that accumulates and flows after heavy rainstorms or snowmelts. Floods occur in all fifty states and around the world. Floods can be caused by several factors: heavy rainfall over a short period, moderate rainfall over a long period, melting snow, hurricane storm surge (a dome of water that builds up as a hurricane moves over water), ice or debris jams on rivers, and dam failures.

Floods can cause great harm to people and property. Floods are the deadliest form of natural disasters, killing more Americans every year than tornados, lightning, earthquakes, and forest fires combined. Due to the potential harm, government agencies work to prevent and predict floods.

Describing Floods

Scientists describe...