Floods

Definition

Floods are the “overflowing of the normal confines of a stream or other body of water or the accumulation of water over areas that are not normally submerged.”

Speed of Onset and Duration

Riverine (i.e., fluvial) flooding can occur as seasonal or flash floods. Seasonal floods are typified by a gradual rise to the flood stage that may extend across large areas over a long duration. Because a relatively gradual accumulation usually causes seasonal floods, warning times are generally sufficient to allow the safe evacuation of nearby communities. Flash floods are characterized by a short-duration, high-volume stream flow and usually occur within six hours of a rain event, after a dam or levy fails, or after the sudden release of water from an ice or debris jam. A brief warning and response time accompany them with the potential for a significant loss of life.

Consequences

Floods have the potential to affect vast numbers of people. They are also relatively common as compared with other disaster hazards. Floods can result in very severe damage to critical infrastructure (e.g., water, power, hospitals). If the affected area is expansive enough, it can also disrupt major societal systems like communications, transportation, energy, commerce, and health care. The global consequence of floods is, therefore, enormous and widespread.

Floods typically cause a relatively low level of injuries but result in massive population displacement (along with an associated loss of shelter, water, food, sanitation, hygiene, and personal safety). Floods may also create secondary hazards like toxic mold, fires, hazardous material releases, and food insecurity. The number of deaths associated with flooding is closely related to the life-threatening characteristics of the flood (rapidly rising water, deep floodwaters, objects carried by the rapidly flowing water) and the victims' behavior.

Floods' long duration and chronic nature are detrimental to mental health and wellness. The long-term effects of flooding on psychological health and chronic disease may be even more significant than on other illnesses or injuries. For many people, the emotional trauma continues long after the water has receded.

Scale

Floods can be notoriously large in scale. For example, during 1961–2020, China's top five most-significant floods affected nearly 900 million people, averaging 180 million per event. By comparison, the largest US flood during that same period occurred in eastern Iowa and affected 11 million.

From: Keim M. Emergency Health: Practical application of public health principles. APHA Press. 2023 pp. 65-66. #emergencyhealth #climatecrisis #apha