This weather phenomenon killed more than 200 people in Valencia

Spanish weather agency Ateca talks of a historic storm and the worst “Gota fria” of the century. Climatologists Erich Fischer and Nicholas Gruber of ETH Zurich explain the background.

Bruno Nellwolf/ch media

Parts of Spain's Valencia region received more than 300 liters per square meter of rain in a few hours on Tuesday night. There were also deaths elsewhere along the coast. The devastation is immense. The Spanish Meteorological Office on Friday announced the highest warning level for heavy rain in several areas in the country's southwest.

What is “Gottafria”?

Gota fría means cold drops. “When cold air pushes southward, a droplet of cold air breaks up and a droplet of cold air forms,” ​​explains Erich Fischer, a climatologist at ETH Zurich. “This creates low-pressure areas, which often Moving slowly and uncontrollably, and causing heavy rainfall, Gota fría is therefore based on strong fluctuations in ocean and air temperatures as the first low Atlantic foothills push across the warm Mediterranean with cold, moist air. , this phenomenon will occur. In September and October.

Why was it raining so hard this storm?

The low-pressure area in Gotafriria rotates counterclockwise, thus transporting large amounts of moist air to the Spanish coast. Subsequently, thunder and lightning clusters formed in the low-pressure area in the Valencia area. “They stay stationary for a few hours in pretty much the same area, and then it rains. There's a lot more rain there than elsewhere along the coast,” Fisher said.

Satellite images show the extent of the damage.Image: U.S. Geological Survey/U.S. Environmental Protection Agency

Nicolas Gruber, a marine expert at ETH Zurich, added: “The extremely high temperatures in the Mediterranean keep evaporation high, creating water vapor, which greatly increases the impact at lower altitudes, and the water vapor then flows in the form of rain or Falling in the form of hailstones.”

Does this “gota fria” phenomenon exist elsewhere?

“We see similar phenomena in tropical cyclones, hurricanes and typhoons,” Gruber said. They get their energy directly from warm ocean water. As a result, these tropical cyclones can rapidly intensify as they pass over particularly warm water. “This effect was seen with the recent Hurricane Milton, which rapidly intensified within a few hours and became one of the most powerful hurricanes in history.”

“A similar situation occurred a few weeks ago in eastern and central Europe, where high water temperatures in the Adriatic enhanced the impact of cold droplets,” Fisher said. Such weather conditions also brought large amounts of rain to Croatia, Austria and the Czech Republic. rainfall.

Is this year’s Gota fría special?

Falling cold air has caused previous flooding in the Valencia region, such as in 1957. “So the cold air drop is here to stay, and the low pressure area may not be particularly strong this week.” “But this event today is in a warmer atmosphere, with warmer, wetter air,” Fisher said. The action was even more intense today as the water was very warm.

Why was Spain so badly damaged this time?

In addition to precipitation, many other factors are important and influence the scale and intensity of flooding and damage. These include soil sealing, deforestation, river damming, and more. “This is likely exacerbating the effects of record high rainfall,” Gruber said.

“The death toll must be particularly high because it affects a very densely populated area,” Erich Fischer said. Water drainage is poor as soil plays a central role in erosion and sealing. “People are dying from flooding in areas where there's not a lot of rainfall but inland rivers overflow their banks,” Fisher said.

Was a mistake made?

The role of flood protection, disaster warning and political accountability must be questioned. Fisher asked: “Why did so many people die in Valencia, but only a few died in Vienna, which is also very densely populated?” Whether this was a coincidence or too little investment in flood control beforehand remains to be investigated. In this regard, Fischer mentioned that flood protection projects in Valais have also been stopped.

What impact does climate change have on such weather events?

“Whether cold air droplets will become more common as climate changes is an exciting but open question for science. We don't have an answer to that question yet,” said climatologist Fisher. This fall's incredible buildup naturally raises the question to what extent this is a coincidence. The only thing that is certain is that today's rainfall will be more extreme during Gota fria.

Gruber said experience shows that global warming is increasing heavy precipitation. “However, it has not been proven whether they will become more common.” Gruber is also concerned about the impact of warmer sea temperatures on marine flora and fauna. (aargauerzeitung.ch)

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