Urban flooding

Urban flooding can occur regardless of whether or not affected communities are located within designated floodplains or near any body of water.

In urban areas, flood effects can be made worse by existing paved streets and roads which increase the speed of flowing water.

This applies in particular to coastal cities which may be affected by sea level rise and higher rainfall intensity.

Impermeable surface areas are generated through soil sealing as this reduces drainage options of floodwaters.

[3]: 925 Some researchers have mentioned the storage effect in urban areas with transportation corridors created by cut and fill.

Several studies have looked into the flow patterns and redistribution in streets during storm events and the implication on flood modelling.

The severity of extreme storm events, including hurricanes and other types of tropical cyclones, are also expected to increase.

In the US, industry experts estimate that wet basements can lower property values by 10%-25% and are cited among the top reasons for not purchasing a home.

[15] According to the U.S Federal Emergency Management Agency (FEMA), almost 40% of small businesses never reopen their doors following a flooding disaster.

[16] In the UK, urban flooding is estimated to cost £270 million a year in England and Wales; 80,000 homes are at risk.

Several studies looked into the flow patterns and redistribution in streets during storm events and the implication in terms of flood modelling.

While these models can be helpful in predicting worldwide effects of global warming and in raising awareness about large-scale impacts, their spatial resolution is often limited to 25 km or more, making them less helpful for local planners in mitigating the effects of climate change on a street-by-street scale.

While gray infrastructure can be effective in preventing flooding-related damage[29] and can be economically valuable,[30] some models suggest that gray infrastructure may become less effective at preventing flood-related impacts in urban areas in the future as climate change causes flooding intensity and frequency to increase.

Green infrastructure includes many types of vegetation, large open areas with pervious surfaces, and even rainwater collection devices.

[39] SuDS efforts make urban drainage systems more compatible with components of the natural water cycle such as storm surge overflows, soil percolation, and bio-filtration.

[42][43] In particular, increasing the percent of land dedicated to open, vegetated space can be helpful in providing an absorption and storage area for storm runoff.

[50] During the summer of 2021, Hurricanes Henri and Ida caused significant flooding in many cities along the east coast of the United States.