Flash floods have become more common as a result of climate change, affecting cities all over the world. Parts of London and the south of England were soaked after severe rains in July. When there is a lot of rain and the amount of water is too much for the drains and sewers to handle, flash floods occur. It can strike at any time and without warning. Floodwaters can make roads unusable, forcing people to leave their vehicles and cause damage to their homes and businesses.

Critical public infrastructure, such as transportation networks and hospitals, can be harmed by floods. Some hospitals in London had to force patients to evacuate after losing power. This form of “surface water” flooding is more frequent in metropolitan locations because of the presence of hard surfaces such as paved front gardens, highways, parking lots, and high streets. When it rains, unlike in the countryside, it does not soak into the earth. An example was observed in July, when Storm Elsa devastated New York City, flooding the subway system.

“If the street drains can’t handle the water, it pours over the curb and makes things worse,” Sarah Feinberg, president of the city’s transportation authority, explained. Water had crept into the subway vents and down the stairwell, she said. Many countries, including much of the United Kingdom, developed old sewer systems based on historical rainfall estimates. The growth of London is also a problem, according to Dr. Veronica Edmonds-Brown of the University of Hertfordshire, because the city’s Victorian-era drainage system “cannot cope with the tremendous rise in population.”