Flash flooding threatens over two-fifths of London’s businesses

More than 126,000 commercial buildings in London are at risk from flash flooding. Climate change will heighten that threat.

Those are the findings of a new study by Zurich Insurance Group, which mapped every commercial and mixed use property in the U.K. capital against areas at risk from heavy rain. Nearly half of all basements used by businesses are threatened by flooding, it found.

Flooding occurs when heavy rains overwhelm drainage systems, with cities at far greater risk than rural areas because they tend to be covered by non-absorbent concrete, while their large populations put pressure on sewage networks. Last July, London was hit twice by flash floods, which closed over a dozen underground train stations, impacted hospitals and paralyzed roads.

The risks are expected to increase because of climate change. Under a high-emissions scenario, with about 3 degrees Celsius of warming by 2070, London can expect to see two-and-a-half times more days where at least 30 millimeters of rain falls in an hour, compared with the 1990s, according to the U.K.’s Met Office. That 30 millimeter-per-hour threshold is typically used to trigger flash flood warnings.

“Flash floods are one of the most serious climate threats facing the capital,” said David Nichols, Zurich U.K.’s chief claims officer. “More frequent and severe rainstorms could be hugely disruptive for Londoners, businesses and the city’s economy. Extreme weather is the new normal, and businesses need to adapt."