Flash floods are a worsening scourge worldwide — here's why

• At least 62 people have been killed in the worst flooding to hit Spain in decades.
• Flash floods are becoming more common and more intense due to global warming.

At least 62 people have been killed and many more are missing in the worst flooding to hit Spain in decades.

Torrential rain hit parts of the country on Tuesday, cutting off main roads, delaying flights, and damaging homes.

The rain was the result of a weather phenomenon known as a cold drop, in which cold air moves over warm water.

The warm air then rises rapidly, leading to the formation of huge cumulonimbus clouds capable of releasing violent downpours that can devastate towns and cities.

Such extreme weather events have a huge human and economic cost — and scientists believe global warming, combined with the way humans have developed the natural landscape, will only make the problem worse.

The cost of extreme weather

Estimates for the economic costs of extreme weather and flooding vary, but many tend to agree that they are on the rise.

According to the European Environment Agency, extreme weather in Europe caused economic losses of assets estimated at more than $800 billion between 1980 and 2023.

Last year, a study by Victoria University of Wellington in New Zealand said the damage caused by the climate crisis through extreme weather has cost $16 million an hour for the past 20 years.

The World Economic Forum calculated that the cost of extreme events had increased nearly eight times globally, inflation-adjusted, since the 1970s.

The impact of flash flooding can be particularly severe because, often, there is very little warning.

Flash flooding in dry areas

Flash floods are different from regular flooding because they develop quickly, in the span of a few hours or even minutes.

They can be far more devastating in dry areas because parched soil tends to repel water rather than allow it to soak in.

That means surges can result from as little as 10 millimeters in just one hour, according to a 2023 article in Nature.

"Our analysis using the Emergency Events Database shows that, since 2000, such regions experienced less than half (47%) of deadly flash floods globally, yet saw almost three-quarters (74%) of related deaths," the authors wrote.

The same researchers found that the rate of dryland flash flooding around the world was 20 times higher between 2000 and 2022 than it was between 1900 and 1999.

Ernesto Rodríguez Camino, a senior state meteorologist and member of the Spanish Meteorological Association, said flash flooding is becoming more frequent, a trend which is set to continue because of the damaging effects of global warming.

"Events of this type, which used to occur many decades apart, are now becoming more frequent, and their destructive capacity is greater," he said.

Why are there more flash floods?

The Environmental Defense Fund (EDF), a US-based nonprofit, said flash flooding has intensified because of increased rainfall and heat waves.

The rise in the world's average surface temperature — which was more than 2 Degrees Fahrenheit warmer in 2020 than it was 100 years ago — has resulted in more moisture and clouds in the air, the organization said.

According to the EDF, modern infrastructure, including buildings, roads, and sidewalks, has eliminated natural landscape features that would have slowed flooding in the past.

It added that stormwater systems designed to protect buildings are often too old and not vast enough to handle the increasing amount of major weather events caused by global warming.

Additionally, houses are continuing to be built in areas that are prone to flooding, the organization said.

The World Health Organization (WHO) said people who live on floodplains or in buildings without flood protections or warning systems are most vulnerable.

What can be done?

Non-environmental factors, such as new infrastructure and better weather warnings, can help prevent the impact of flash flooding.

Jess Neumann, an associate professor of Hydrology at the University of Reading, said that a long-term solution would involve the "radical redesign of urban areas."

"Flash floods can affect anyone, anywhere. We take preparation for other hazards such as earthquakes and tsunamis very seriously with education, drills, and emergency kits," she said. "It is time we afforded the same to flood risk preparedness."

John Marsham, a professor of atmospheric science at the University of Leeds, agrees with Neumann's assessment.

"Our entire infrastructure and civilization are based around a climate that no longer exists," he said, adding that some locations are becoming more difficult to insure against flood damage.

Some cities are already considering better precautions for extreme weather events. For example, in 2022, the US Army Corps of Engineers unveiled its proposal to build a $52 billion moveable sea barrier along the New York Harbor to protect against storm surges.

These protections would also allow local economies to recover faster.

The EDF reported that the average flood event from excessive rainfall in the US costs around $4.7 billion.

Marsham and Liz Stephens, a professor in climate risks and resilience, said that local governments should also implement stronger warnings about the risks of flash flooding to prevent death and injuries.

"People shouldn't be dying from these kinds of forecasted weather events in countries where they have the resources to do better," Stephens said.