Floods are the most frequent and costly natural hazard in the United States, leading to many deaths and, as a result of the severity, result in the most frequent presidential disaster declarations for natural or weather-related events. Millions of people live in flood-prone areas in the United States, where repetitive flooding causes additional damage in already damaged areas. There are very large population concentrations in many of these flood-prone areas and therefore the opportunity for huge costs and substantial injuries and potential deaths continues to increase. Destruction of wetlands in order to erect buildings in prime areas has contributed substantially to this problem. Large numbers of people live in areas that may either flood occasionally or not flood at all, but because of new conditions in the area such as the aftermath of wildfires or because of changing weather patterns and conditions, flooding may now occur. Floods may be caused by: tidal surge, severe thunderstorms, oversaturation of soils, and spring thaw of frozen land, snow, and ice; heavy rains from tropical storms, hurricanes, tornadoes, and other severe weather events; and the topping or destruction of levees and dams. A flash flood, which may be caused by a slow-moving storm, is a rapid filling of a low-lying area in less than 6 hours, however it can occur in a matter of minutes. The force of the water can cause landslides, move boulders, rip out trees, and damage or destroy various structures, roadways, and bridges. It can also inundate water and sewage systems, electrical systems, communications systems, and all means of rescue. Areas of wildfires denude the land and make it vulnerable to mudslides and flooding when heavy rains occur.
There are numerous potential health and safety consequences of floods. They include drowning or near drowning; substantial injuries from structures, debris, etc.; electrical hazards from downed power lines and wet appliances; potential explosions and fires from disrupted gas lines;
hypothermia from working in a wet environment; infectious diseases; chemical contamination from household chemicals, industrial chemicals, fertilizers, and pesticides; carbon monoxide poisoning from unvented gas-powered equipment; respiratory problems from mold and exposure to wet conditions; bites and transmission of disease by rodents and sick animals; exacerbation of chronic diseases such as asthma, allergies, and ear, nose, and throat infections; mental health problems especially in children; antisocial and violent behavior and rioting; and poor nutrition due to lack of safe food and water supplies.