The weather events that are thought to have contributed to extreme floods in western Europe are becoming more likely due to climate change, according to climate and meteorology researchers.
A combination of extremely heavy rainfall and a slow-moving storm front most likely contributed to the flooding, which has , and has also affected the Netherlands, Luxembourg and Switzerland. 鈥淚t鈥檚 come from very moist air in the atmosphere wrapping around an almost stationary front,鈥� says at Newcastle University in the UK.
Both weather events are becoming more likely due to global warming.
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鈥淥ne of the best understood consequences of global warming is that the moisture content in the atmosphere increases,鈥� says at the University of Leipzig in Germany. With every degree Celsius increase in warming, the amount of water the atmosphere can hold goes up by 7 per cent, he says 鈥� and this .
At the same time, accelerated warming at Earth鈥檚 poles relative to the equator means the frequency of slow-moving storm fronts is also growing, increasing the probability of sustained rainfall over specific areas of land 鈥� such as the continuous heavy rainfall that has caused the flooding in western Europe.
鈥淲hat鈥檚 made the difference, I think, in this event, is that this low pressure system was almost stationary and the band of rain within was moving in the direction of the flow of this low pressure system as well, so it was very much rain falling on the same system again and again and again,鈥� says Fowler.
A by Fowler and her team found that these types of slow-moving or almost stationary storms may be 14 times more frequent across land in Europe by the end of the century. 鈥淚t鈥檚 a huge increase,鈥� she says.
That study modelled what might happen under a high greenhouse gas emissions scenario, but Fowler says that limitations in climate modelling generally mean that we may still be underestimating how quickly weather events might intensify. 鈥淐limate models don鈥檛 necessarily produce feedback from the land surface very well,鈥� she says.
鈥淲e seem to be seeing more severe rainfall events and flooding, [and] big heat waves. We鈥檙e seeing more and more of these extremes,鈥� says Fowler. 鈥淥ur climate models are not projecting these sort of changes for a few decades to come, so I find it quite scary as a climate researcher, actually, some of these events that we鈥檙e seeing around the world this year.鈥�
The same storm system that has affected Germany, Belgium, the Netherlands and Switzerland hit the UK a few days earlier, says Fowler, which led to .
at the Royal Netherlands Meteorological Institute says that the reason the flooding had more severe consequences in continental western Europe is because of the geography of the region. 鈥淢ost rain fell on the eastern side of the Ardennes hills,鈥� he says. 鈥淚f you have moist air approaching a mountain range then it has to go up to go above it 鈥� and, because it goes up, it cools and the moisture condenses as rain. So you always get much more rain on the windward side of a hill or mountain.鈥�
But Quaas says that more extreme flooding similar to that seen in continental western Europe could affect London in the future. 鈥淪ometime in the future it will happen to London,鈥� he says.
Fowler agrees. 鈥淐limate change affects everyone,鈥� she says. 鈥淲e鈥檙e already seeing climate change and all of our current weather events are affected by the warmer climate that we live in.鈥�
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