Recent floods in France linked to climate change

Recent floods in France linked to climate change

A team of scientists has found that deluges like the recent floods in France, which caused 18 deaths and nearly one billion Euros in damage, are at least 40 percent — and as much as 90 percent — more likely in the areas of France they studied.

Results from the World Weather Attribution partnership (WWA) are useful in communicating the changing risks of extreme weather to the public, say the scientists. Publishing findings at the time of the event, in near real-time, helps to raise awareness of the issues.

Climate Central reports:

"The rains began falling in parts of western Europe on May 26, thanks to a large low pressure system that parked over the area. The situation played out slightly different in France and Germany: While small thunderstorms popped up across southern Germany and dumped rain over small areas, more widespread rains fell for days across northern France.

In Gundelsheim in the German state of Baden-Württemberg, 4.8 inches of rain fell in the 24 hours beginning at 6 a.m. on May 29. The onslaught triggered flash floods that tore through towns, sweeping away cars and leaving streets clogged with debris.

In France, the swollen Seine peaked at 20 feet above its normal height on June 3, the highest it has been in more than 30 years. The Louvre was closed so that works of art in the areas most vulnerable to flooding could be moved to safety, while the 16th century Chambord castle to the south of Paris was inundated.

In general, it is expected that heavy downpours will increase as the world warms due to the buildup of heat-trapping greenhouse gases in the atmosphere, because a warmer atmosphere contains more moisture. But other factors, like changes to the circulation patterns that drive storms, can complicate the picture on more regional and local scales.

Both influences are factored into the WWA analysis, conducted by researchers at the Royal Netherlands Meteorological Institute (KNMI), the University of Oxford, France's Laboratory for Climate and Environment Sciences, the Institut Pierre­-Simon Laplace, and the Red Cross Red Crescent Climate Centre.

The analysis uses methods that have already been peer-reviewed, including examining the change in occurrence of such extreme rains in the historical record and in climate models, as well as using finer-scale regional climate models to compare the current climate to one without warming.

Because the meteorological situations differed in France and Germany, the team used slightly different measures. In Germany, where the rains fell over a shorter period, they examined the one-day maximum precipitation for the hardest hit region, while for France, where rains were longer-lasting and more widespread, they looked at the three-day averaged precipitation for the Seine and Loire river valleys.

For France, they found that the torrential rains that fell from May 29-31 in the Seine basin were very rare, happening once in every few hundred years. In the Loire, it was about once every 50 years.
But the risks are increasing in both regions, with such an event at least 40 percent more likely to occur in the springtime with warming, but up to 80 percent in the Seine region and 90 percent in the Loire.
For Germany, the rains had a 1-in-20 chance of occurring somewhere in southern Germany in any given year. But while the historical observations showed a decreasing trend, climate models suggested such events should increase. The reasons for the discrepancy are something the team hopes to work out later."

One of the models used in the study, Weather@home, is a group of regional climate modelling experiments within climateprediction.net, a volunteer computing and climate modeling project based at the University of Oxford in the Environmental Change Institute, the Oxford e-Research Centre and Atmospheric, Oceanic and Planetary Physics.

With climateprediction.net, scientists are able to design experiments that answer questions that otherwise could not be answered without large climate model ensembles. However, most extreme weather events take place on a much smaller scale that the global models can't show. That's where the weather@home project comes in, running regional climate models to investigate how climate change affects our weather.

[Acknowledgements to Climate Central for information used in this article]