Cities across the world are affected by flash floods, which have become increasingly common as a result of climate change. After torrential rains in July, parts of London and the south of England were flooded. Flash floods usually occur when there is a lot of rain and the amount of water is too great for the drains and sewers to handle. It can happen unexpectedly and without warning. Floodwater can make roads impassable, causing vehicles to be abandoned and causing damage to houses and businesses.

Floods can impact negatively critical public infrastructure, such as transportation networks and hospitals. After losing power, some hospitals in London had to order patients to leave. Because of the abundance of hard surfaces in urban areas, such as paved front gardens, roads, parking lots, and high streets, this type of “surface water” flooding is more likely. When it rains, it doesn’t soak into the ground as it does in the countryside. In July, when New York City was devastated by Storm Elsa, which flooded the subway system, an example was seen.

“If the drains at the street level can’t handle the water, it goes over the curb and makes things even worse,” said Sarah Feinberg, president of the city’s transit authority. She claimed that water had gotten into the subway vents and down the stairwell. Old sewer systems were designed in many countries, including much of the United Kingdom, based on historical rainfall estimates. According to Dr. Veronica Edmonds-Brown of the University of Hertfordshire, the development of London is also a concern because the city’s Victorian-era drainage system “cannot cope with the massive rise in population.”