European Flood Trends Vary from North to South

By Eric Roston | August 29, 2019

European river flooding has grown more intense in northwestern Europe and decreased in the south over the last half century, according to a study by nearly four dozen researchers. The work, which is the first documentation of long-term flood trends across Europe based on observational data, may help the region see and prepare for new patterns of risk in the years ahead.

The study, published Wednesday in Nature, focuses on river basins, which gives it a more macro view of flood-related issues and mitigates local problems like land-use and development. Past studies have focused on individual countries, not the entire continent.

“The flood changes identified here are broadly consistent with climate model projections for the next century,” the authors write, “suggesting that climate-driven changes are already happening and supporting calls for the consideration of climate change in flood risk management.”

In the northwest, a jump in extreme rainfall has led to increased flooding, more than 11% per decade above the average river flow. To the south, lower amounts of rainfall and evaporation brought on by higher temperatures led to a 23% drop. Parts of Eastern Europe also saw diminished flooding, driven by less snow cover and resulting snow-melt.

Two factors may make it a challenge for flood managers to put the study’s conclusions into action, said Wouter Berghuijs, a hydrology specialist at ETH Zurich. The new research didn’t identify a cause of the rise in historical flooding. Also, it doesn’t capture small-scale flooding, which could be much lower or much higher than the regional trend, he said.

Still, “with many rivers crossing the borders of countries, successfully addressing flood risks relies on understanding large-scale changes, which are very well exposed in this new study,” Berghuijs said.

The work on Europe aligns with two other studies published this week, including an assessment that the continent is heating up faster than scientists expected.

The other, a new study in Geophysical Research Letters examining winter rainfall patterns since 1920, found human activity influenced those patterns in the Northern Hemisphere. Clara Deser, a senior scientist at the National Center for Atmospheric Research and a co-author of the study, also reviewed the work on European river flooding and found it to align with her work finding a century-scale human fingerprint on precipitation.

Günter Blöschl of the Vienna Institute of Technology, and the lead author of the Nature study, also emphasized his work wasn’t about linking the half-century history of flooding to climate change. But he said it is worth noting the similarity of his results to formal projections of Europe’s future.

“This is one of the reasons why I believe that what we’ve seen, the data in the past, can also be carried forward to the future,” he said.

Photograph: In this photo taken on Aug. 02, 2019, people make their way through flooded roads after heavy rainfalls in Berlin, Germany. Photographer: Michael Kappeler/dpa via AP.

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