Flood

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Inundation
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Urban flooding in a street in Morpeth, England

A flood is an overflow of water (

increased rainfall and extreme weather events increases the severity of other causes for flooding, resulting in more intense floods and increased flood risk.[2][3]

Flooding may occur as an overflow of water from water bodies, such as a

domestic animals
.

Floods can also occur in rivers when the flow rate exceeds the capacity of the

vector-bourne disesases transmitted by mosquitos.[5]

Types

View of flooded New Orleans in the aftermath of Hurricane Katrina.
Flooding of a creek due to heavy monsoonal rain and high tide in Darwin, Northern Territory, Australia.
Flood in Jeddah, covering the King Abdullah Street in Saudi Arabia.

Areal

In spring time, the floods are quite typical in Ostrobothnia, a flat-lying area in Finland. A flood-surrounded house in Ilmajoki, South Ostrobothnia.

Floods can happen on flat or low-lying areas when water is supplied by rainfall or snowmelt more rapidly than it can either

series of storms. Infiltration also is slow to negligible through frozen ground, rock, concrete, paving, or roofs. Areal flooding begins in flat areas like floodplains and in local depressions not connected to a stream channel, because the velocity of overland flow depends on the surface slope. Endorheic basins may experience areal flooding during periods when precipitation exceeds evaporation.[6]

River flooding

Floods occur in all types of

normally-dry channels in arid climates to the world's largest rivers. When overland flow occurs on tilled fields, it can result in a muddy flood where sediments are picked up by run off and carried as suspended matter or bed load. Localized flooding may be caused or exacerbated by drainage obstructions such as landslides, ice, debris, or beaver
dams.

Slow-rising floods most commonly occur in large rivers with large

tropical cyclones
. However, large rivers may have rapid flooding events in areas with dry climates, since they may have large basins but small river channels, and rainfall can be very intense in smaller areas of those basins.

Flash flood in Ein Avdat, Negev, Israel

Rapid flooding events, including

convective precipitation (intense thunderstorms) or sudden release from an upstream impoundment created behind a dam, landslide, or glacier. In one instance, a flash flood killed eight people enjoying the water on a Sunday afternoon at a popular waterfall in a narrow canyon. Without any observed rainfall, the flow rate increased from about 50 to 1,500 cubic feet per second (1.4 to 42 m3/s) in just one minute.[7]
Two larger floods occurred at the same site within a week, but no one was at the waterfall on those days. The deadly flood resulted from a thunderstorm over part of the drainage basin, where steep, bare rock slopes are common and the thin soil was already saturated.

Flash floods are the most common flood type in normally-dry channels in arid zones, known as

arroyos in the southwest United States and many other names elsewhere. In that setting, the first flood water to arrive is depleted as it wets the sandy stream bed. The leading edge of the flood thus advances more slowly than later and higher flows. As a result, the rising limb of the hydrograph
becomes ever quicker as the flood moves downstream, until the flow rate is so great that the depletion by wetting soil becomes insignificant.

Coastal flooding

Coastal areas may be flooded by storm surges combining with high tides and large wave events at sea, resulting in waves over-topping flood defenses or in severe cases by tsunami or tropical cyclones. A storm surge, from either a tropical cyclone or an extratropical cyclone, falls within this category. A storm surge is "an additional rise of water generated by a storm, over and above the predicted astronomical tides".[8] Due to the effects of climate change (e.g. sea level rise and an increase in extreme weather events) and an increase in the population living in coastal areas, the damage caused by coastal flood events has intensified and more people are being affected.[9]

Flooding in

barometric pressure
and large waves meeting high upstream river flows.

Urban flooding

Flooding on Water Street in Toledo, Ohio, 1881

Catastrophic

Catastrophic riverine flooding can result from major

volcanic eruption. Examples include outburst floods and lahars. Tsunamis can cause catastrophic coastal flooding
, most commonly resulting from undersea earthquakes.

Causes

Flood due to Cyclone Hudhud in Visakhapatnam