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Climate change raises river levels

Climate change raises river levels

Climate change not only means that it is getting warmer on Earth, but also that precipitation levels are changing. If heavy rainfall causes rivers to swell, it can lead to devastating floods. Scientists have now analyzed the severity of such flood events in Europe.

Accordingly, the extent of river floods in recent years but it has increased in the east and south of the continent. The main cause of these developments is climate change. This is the result of the most comprehensive study to date on this subject  and that was published on Wednesday in the journal “Nature” changed. With the current study, the scientists now wanted to find out whether the severity is also affected. Thanks to the pan-European cooperation, it was now possible for the first time to access a huge amount of data.

Overall, the scientists around the study leader Günter Blöschl of the Vienna University of Technology analyzed data from around Period of time from to 2010. These measuring points record how much water a river carries at a given time. As floods, the researchers defined the largest amount of water per unit time (called “runoff”) in the respective year.

Heavier floods in northwestern Europe

The scientists draw no uniform picture for Europe. In the north-east of the continent, for example, the extent of river flooding has increased significantly over the past half-century. The largest increase was observed in the north of England and in the south of Scotland. There, the amount of water in flood increased by eleven percent over the long-term average per decade.

An important cause is changes in the atmospheric circulation, says lead author Günter Blöschl: “The large depressions draw slower and further north over Europe.” When the soil is almost saturated, any further rainfall contributes to the increase in river levels.

“As winter precipitation in northwestern Europe has risen in recent decades, so has the magnitude of river floods,” said Bruno Merz, hydrologist at Potsdam’s Geoforschung Center (GFZ) and co-author of the study, the Tagesspiegel.

Less precipitation, more flash floods

The situation is different in the south and east of Europe. There, the rivers lead in flood ever less water. In parts of Russia, the amount per decade has even decreased. “In Russia, the temperature has increased by about two degrees,” says Blöschl. This means less snow, and thus also the risk of flooding. This is because in winter more precipitation than rain and less than snow falls. This is why some of the water already flows off in winter and does not cause any flood during the snowmelt in the spring.

In southern Europe, however, there is less precipitation than in the past, as rising temperatures cause more and more water to evaporate from the soil , which also affects the flow levels. Merz emphasizes that parallel to this trend in southern and eastern Europe, more and more flash floods are to be expected. These short-lived, small-scale precipitations are often triggered by thunderstorms and are influenced by climate change, for example because warm air can absorb more water.

More flood in southern Germany, less in Berlin

According to Bruno Merz, Germany is in a transition zone. Larger parts are characterized by winter floods, in the south and east, however, the floods tend to occur in the summer. “The observations point to an increase in flood severity in the south and a decline in northeast Germany,” says Merz. The data show a significant increase, especially in parts of Bavaria, while in the northeast with Berlin and Brandenburg there is a decreasing trend in flood severity.

The researchers write that their results show the most unambiguous link between climate change and flood events so far. It is not at all easy to filter out the effect of man-made climate change from the observation data. The data also includes many other influences, such as natural climate variations, the construction of retention basins, river engineering measures or changes in agricultural use. “Because of the many factors,” says Merz, “one would normally expect little consistent patterns in space.” But the researchers have found just such patterns.

Merz says the results are pretty much accurate over larger regions The changes in climate variables such as precipitation, snowmelt or soil moisture, which the researchers had expected, fit in. “Precisely because we see regional patterns and because these patterns are consistent with changes in climate variables, it can only be the climate.”

Scientists do not anticipate trends for the future, but believe that based on climate models, current precipitation and temperature trends are likely to continue over the next few decades, which could significantly increase flood risk in many areas of Europe.

Already, overflowing rivers cause damage of more than (billions) of (billions of) a year to 196. This has disastrous consequences for hundreds of thousands of people who lose their livelihoods.

The authors therefore emphasize the importance of a Europe-wide long-term monitoring of flood events. In addition, for example, you have to create buildings in such a way that they are in  or Also in the construction of dykes and flood retention basins you have to pay attention to the new findings. “It is necessary to think about climate change in flood protection.”(with dpa)

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