A flood occurs when water overflows its usual boundaries, submerging land that is typically dry. Floods represent a significant environmental concern impacting agriculture, infrastructure, and public health. Understanding their diverse origins, wide-reaching consequences, and safety implications is important for communities worldwide.
The Diverse Nature of Floods
Floods manifest in various forms, each triggered by distinct environmental conditions. Heavy rainfall is a primary cause, leading to excess water that the ground cannot absorb, resulting in runoff that overwhelms rivers and drainage systems. Rapid snowmelt, especially when combined with spring rains, can also contribute to river levels rising and overflowing their banks. Additionally, storm surges, which are abnormal rises of water generated by strong winds from coastal storms like hurricanes, can cause significant coastal flooding. Dam or levee failures, although less common, can unleash a sudden and catastrophic release of water, creating devastating flood events.
Different types of floods are categorized by their characteristics and locations. Riverine floods, also known as fluvial floods, happen when rivers or streams exceed their capacity and spill onto adjacent floodplains. Flash floods are characterized by their rapid onset, occurring within minutes or a few hours of intense rainfall or a sudden release of water, often in dry creeks or urban areas. Coastal floods result from seawater inundating low-lying coastal land, typically due to storm surges, high tides, or tsunamis. Urban flooding occurs when rainfall overwhelms the drainage systems in cities, even in areas not near natural bodies of water, often exacerbated by impervious surfaces like roads and buildings.
Global Reach and Impact
Floods are globally prevalent, occurring in every U.S. state and territory, and are the most frequent type of natural hazard worldwide. They account for a substantial portion of all recorded natural disaster events. Between 1990 and 2022, over 4,700 flood events were recorded across 168 countries, affecting billions of people.
The consequences of floods extend to economic and human impacts. Economically, floods caused over $1.3 trillion in damages globally between 1990 and 2022, with China experiencing the most economic loss at $442 billion. Property damage affects homes, businesses, and infrastructure, with recovery costs often high. Floods lead to displacement, injuries, and loss of life, with drowning being the leading cause of flood-related fatalities. Between 1998 and 2017, floods affected more than 2 billion people globally, and from 1990 to 2022, they caused over 218,000 deaths.
Understanding Flood Safety
Even shallow floodwaters possess power and can pose a threat. As little as six inches of swiftly moving water can knock an adult off their feet. Just one foot of moving water is capable of floating many vehicles, and two feet of rushing water can carry away most automobiles, including larger vehicles like SUVs and and pickup trucks. This demonstrates that seemingly minor depths can hide force, making floodwaters dangerous to navigate on foot or in a vehicle.
A safety principle during flood events is “Turn Around, Don’t Drown.” This advises against driving or walking through flooded areas, as the depth of the water is often deceptive and the current can be strong. If floodwaters rise around a car, it is safer to abandon the vehicle and move to higher ground. Floodwaters can also be contaminated with sewage, chemicals, and debris, posing health risks from infections and exposure to hazardous materials, so direct contact should be avoided.