Climate Crisis Is Going to Make Europe Even Stormier

On July 13, a storm system moved over Belgium and western Germany, pouring down up to about 6 inches (15 centimeters) of rain in just 24 hours. The resulting deluge swept away homes and cars and killed at least 196 people as of July 20, surprising scientists with the extent of the devastation. 

The same week, Newcastle University reported on a new study warning that devastating rainstorms could be an increasing part of Europe's future if nothing is done to reduce greenhouse gas emissions. The paper, published in Geophysical Research Letters, found that slow-moving, intense rainstorms could become 14 times more frequent over land by the end of the century, with significant impacts for the people and communities they fall on.

“The most important effect of high increase in such slow-moving intense rainstorms would be a high increase in flash floods frequency, and intensity as well,” study lead author Dr. Abdullah Kahraman of Newscastle University tells Treehugger in an email. “The current urban infrastructure,” he says, such as drain systems, “might not respond well to the new extremes.”

Slow and Wet

It is well established at this point that the climate crisis increases the chance of extreme precipitation events. This is because warmer temperatures lead to more evaporation, meaning there is more moisture available in the air when storms roll through. Further, the additional moisture also gives storms more energy, as the faster condensation of water vapor leads to more vertical motion within storm clouds.

However, another concern is that climate change might make these wetter storms slower in some regions. Slow-moving rainstorms can be extremely dangerous. This was what happened with Hurricane Harvey in 2017, for example, which stalled over South and Southeast Texas for days, leading to deadly flooding. However, studies that project future rainfall tend to overlook this factor. 

The new research corrects for this by incorporating storm speed into their model for what would happen to rainstorms in Europe under a worst-case emissions scenario. The researchers from Newcastle University and the United Kingdom’s Met Office used detailed climate simulations located at the Met Office’s Hadley Center. They looked at current and future European environments to assess them for two key metrics:

1. Extreme Precipitation Potential (EPP): The ability of an environment to generate heavy rates of rainfall.
2. Slow-moving Extreme Precipitation Potential (SEPP): The ability of an environment to generate heavy rainfall that is also almost stationary.

They found that, by the end of the century, environments in Europe with the potential for heavy rainfall would increase by a factor of 7, while environments with potential for almost-stationary storms would increase by a factor of 11 overall and 14 over land.

This is currently not the norm for Europe, especially when it comes to SEPP. While most of Europe does now have the potential to generate heavy rains, slow-moving heavy rains are uncommon. But this is set to change.

“By 2100, in summer (especially August), SEPPs cover the entire continent, despite being very rare in today's climate in any month . . . with likely serious consequences for future flood risk,” the study authors write. 

The reason for this change is not a universal rule of warmer temperatures, like greater evaporation making clouds wetter.

“[T]he changes in temperature over the polar regions and tropics is not the same,” Kahraman explains. “Simulations suggest that high latitudes warm much more than lower latitudes, which results in a reduction in upper-atmosphere wind speed. With these winds slowing down, the storm systems are also getting slower.”

The slower-moving storms highlighted by the study are also slightly different from what happened in Belgium and Germany this summer, he points out. That’s because those storms were caused by a high-altitude band of moisture wrapping around a slow-moving low-pressure system. The study, however, focused on more local systems.

“However, the case would still be captured by one of our developed metrics for tracking rainfall intensity,” he adds.

Flood Warnings

What this summer’s floods and the study’s results also have in common is their status as warnings about the consequences of unchecked climate change. 

Kahraman says policymakers can act on these warnings by improving drainage systems and urban planning.

His co-author and Newcastle University Professor Hayley Fowler agrees.

“This, alongside the current floods in Europe, is the wake-up call we need to produce improved emergency warning and management systems, as well as implementing climate change safety factors into our infrastructure designs to make them more robust to these severe weather events,” he says in the Newcastle press release.

Further, Kahraman notes, it’s not too late to reduce the greenhouse gas emissions ultimately responsible for the heavier, slower storms.

“We don’t have a third simulation to assess the impacts with a lower emissions scenario yet,” he tells Treehugger, “but it is very likely that we will avoid the worst with such measures.”