At least 95 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 air warms up and 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 the climate crisis 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.
"Events of this type, which used to occur many decades apart, are now becoming more frequent, and their destructive capacity is greater," Ernesto Rodríguez Camino, a senior state meteorologist and member of the Spanish Meteorological Association said.
Why are there more flash floods?
Rainfall events are becoming more severe and sudden because of a simple law of physics: Warmer air holds more moisture.
That means that the warming atmosphere can carry more and more water vapor, driving fiercer rain events.
At the same time, the air pulls more moisture out of the ground and plants, driving drought.
In many places across the globe, this is causing more violent and sudden swings between drought and flood extremes. Daniel Swain, a climate scientist who studies the phenomenon at the University of California, Los Angeles, calls it "hydroclimate whiplash," or simply "weather whiplash."
"You can really go to any continent, in any season, and find something at this point," Swain told BI in January 2023, after a cyclone walloped drought-stricken California with devastating rains.
As countries, companies, and entire industries continue burning fossil fuels for energy, causing global temperatures to continue rising, this whiplash will likely get worse.
What's more, our cities, towns, and other infrastructure are not prepared.
According to the Environmental Defense Fund (EDF), a US-based nonprofit, 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 climate change.
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.
Critically, scientists say, industries and countries across the planet must drastically cut their greenhouse-gas emissions to slow the rise of global temperatures. Otherwise, flooding is likely to get worse and worse throughout the rest of the century.
Jess Neumann, an associate professor of Hydrology at the University of Reading, said that another 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.
