What We Know About the Climate Link to European Floods

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images from germany surprising and scary: Houses, shops and streets in picturesque towns and villages along the Ahr and other rivers were violently washed away by fast-moving floodwaters.

The flooding was caused by a storm that slowed down in parts of Europe on Wednesday, bringing up to six inches of rain to the area near Cologne and Bonn before finally starting to subside on Friday. Flooding also occurred in Belgium, the Netherlands and Switzerland, but the worst effects were in Germany, where the official death toll passed 125 on Friday and is certain to climb.

The storm was a frightening example of extreme weather, with a month of rain falling in one day in some places. But in the age of climate change, extreme weather events are becoming more common.

The question is, how much has climate change affected this particular storm and the resulting flooding?

A full answer will have to await analysis that is almost certain to be undertaken given the magnitude of the disaster, which will seek to find out if climate change has made this storm more likely, and if so, by how much.

But for many scientists, the trend is clear. “The answer is yes – all major weather these days is affected by changes in climate,” said Donald J. Wuebbles, professor of atmospheric sciences at the University of Illinois.

Already studies Have shown The Intergovernmental Panel on Climate Change, the United Nations-sponsored group reporting on an increase in heavy showers as the world warms and the science and effects of global warming, The frequency of these events will increase because temperatures keep rising.

“The observed increase is stronger than we expected,” said researcher Geert Jan van Oldenborgh, of the Royal Netherlands Meteorological Institute, in studies of extreme precipitation events in the Netherlands.

Dr. van Oldenborgh is one of the leading scientists. World Weather Relation, a loose group that quickly analyzes certain extreme weather events in relation to any climate change impacts. The newly finished group said a quick analysis They were debating whether to investigate the German floods, heralding the heatwave that hit the Pacific Northwest in late June.

One reason for stronger downpours has to do with fundamental physics: warmer air holds more moisture, making it more likely that a given storm will produce more precipitation. Earth has warmed slightly more than 1 degree Celsius (about 2 degrees Fahrenheit) since the 19th century, when societies began pumping massive amounts of heat-trapping gas into the atmosphere.

For every 1 degree Celsius of warming, the air can hold 7 percent more moisture. As a result, “The intensity of such storm events will increase,” said Hayley Fowler, professor of climate change effects at Newcastle University in England.

And although it is still a matter of debate, there are studies suggesting that rapid warming in the Arctic affects the jet stream by reducing the temperature difference between the northern and southern parts of the Northern Hemisphere. Dr. One effect in the summer and fall is the high altitude, weakening and slowing of the airflow surrounding the sphere, Fowler said.

Dr. “This means that storms have to move more slowly,” Fowler said. He noted that the storm that caused the last flood was almost stationary. The combination of more humidity and a stalled storm system can lead to extra heavy rains in a particular area.

Kai Kornhuber, a climate scientist at Columbia University’s Earth Institute, said: his and colleagues’ research, and papers other scientistsdrew similar conclusions about decelerated weather systems. “They all point in the same direction—summer mid-latitude circulation, jet stream, pointing down and forming a more persistent weather pattern,” meaning extreme events like heat waves and heavy rains are likely to continue.

Michael E. Mann, a climate scientist at Penn State University, has studied the effects of a different type of summer jet stream phenomenon known as the summer season. “wave resonance” in locking air systems in place.

Climate change is making still-weather events more frequent, he said. But he said it was too early to say that the European disaster was caused by wave resonance.

Jennifer Francis, a senior scientist at the Woodwell Center for Climate Research in Massachusetts, said there could be many causes of slowing weather systems, but they don’t usually occur in a vacuum.

The European storm is “part of this big picture of extremes we’re seeing across the Northern Hemisphere this summer,” he said, which includes America’s heat in the Western and Pacific Northwest, heavy rainfall in the Midwest, and cooler temperatures. Heat waves in Scandinavia and Siberia.

Dr. “It is never in isolation when it comes to a strange configuration of the jet stream,” Francis said. “One end in one place always accompanies different kinds of endpoints.”

“It’s all connected and essentially the same story,” he added.

However, when it comes to flooding, there are other factors that can complicate and complicate any analysis of the impact of climate change.

First, local topography must be taken into account, as this can affect precipitation patterns and how much water flows into which rivers.

Human influences can complicate an analysis even more. For example, development near rivers often replaces open land that can absorb rain with buildings, streets and parking lots that increase the amount of water flowing into rivers. Infrastructure built to cope with heavy flow and rising rivers may be poorly designed and inadequate.

And meteorological conditions can sometimes lead to different results.

A 2016 study by World Weather Attribution During floods in France and Germany in May of that year, climate change was found to affect the French flooding caused by three days of rain. But the situation in Germany was different; The flood was caused by a one-day storm. Computer simulations did not find that the likelihood of shorter storms increased in that area in a changing climate.

Some developments can make flooding worse, while other projects can reduce flooding. The situation seems to be the same in the Netherlands, which was not affected much by the storm.

Nathalie Asselman, who advises the government and other clients on flood risk, said that after several major floods on the Meuse River in the 1990s, the Dutch government launched a program called the River Chamber to reduce the risk of flooding.

The work included lowering and widening river beds, lowering flood plains, and digging side channels. “The purpose of these measures is to reduce flood levels,” he said.

While in a ditch near the Meuse in South Holland suffered a violation The measures, which caused some flooding, appear to be working until they are fixed on Friday.

Ms Asselman said flood levels on the Meuse were about a foot lower than they would have been without them. This meant that smaller tributaries backed up less and produced less flooding when they encountered the Meuse.

“The situation would have been worse if we had not implemented these measures,” he said. “Both on the main river and on the tributaries.”

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