A flood zone is a geographic area that has been mapped and classified according to its risk of flooding. In the United States, the term is most often used in relation to the Federal Emergency Management Agency (FEMA) Flood Insurance Rate Maps, which designate zones that indicate the likelihood of flooding in a given year. These designations are used for building codes, land-use planning, flood insurance requirements and emergency management.
For example, homes in FEMA high-risk zones (often called “100-year floodplains”) are required to carry flood insurance if they are mortgaged. Internationally, the meaning of “flood zone” varies by country and context. In the United Kingdom, flood zones are set by the Environment Agency and are defined by probabilities of river or coastal flooding. In the European Union, flood zones are often tied to EU Floods Directive requirements, which mandate mapping of areas with high, medium and low flood probability. In parts of Asia and Africa, “flood zone” may be used more generally to refer to regions subject to seasonal or monsoon flooding, even if not formally mapped by a national agency.
Across all contexts, the underlying concept is the same: a flood zone identifies land at risk of being inundated by water, but the criteria, terminology and enforcement mechanisms differ depending on local governance, law and climate.