Attribution study shows connection – solidarity

Climate change, the floods of the Aher and Erft rivers – and the question of guilt

Climate change has increased the likelihood and intensity of heavy rainfall in Western Europe. This is one result Investigating the Global Weather Attribution Initiative*dated August 23, 2021, which examined the role of climate change in the torrential rains and devastating floods from July 12 to 15 on the Ahr and Erft rivers in Germany and on the Meuse river in Belgium.

Floods in Marinthal, Drnau – Photo © with kind permission HwK Koblenz

The New study from WWA Regarding the torrential rains in Western Europe in July this year, the conclusion is that the probability of such heavy rains has increased by 1.2 to 9 times as a result of man-made warming so far. The intensity of intense precipitation, that is, the amount of precipitation, increased by between 3 and 19 percent. The researchers cautioned against allowing a wide range of their findings to mislead them into underestimating the consequences of global warming. The trend is clear.

*) Scientific studies that have undergone a peer-review process are usually published a year or more after the event, if public interest has already shifted to other events and questions about reconstruction or resettlement are answered without scientific knowledge of the role of climate change taken in consideration. The World Weather Attribution (WWA) – Initiative, a collaboration between climate scientists from Oxford University (UK), KNMI (Royal Meteorological Institute, The Netherlands), IPSL/LSCE (Scientific Institute for Climate and Environment, France), Princeton University and NCAR (National Center for Atmospheric Research, USA). ), ETH Zurich (Switzerland), the Indian Institute of Technology Delhi (Indian Institute of Technology) and climate impact specialists from the Red Cross/Red Crescent Climate Center (RCCC) worldwide, were established to change this and create a robust assessment of the role of climate change in the impact of climate change. the event. This initiative is led by Frederic Otto (University of Oxford) and Geert Jan van Oldenburg (KNMI).

An event 4 to 500 years or less – more frequent due to climate change

For the analysis, the researchers compared today’s climate to the climate before the average global temperature rose by 1.2 degrees since the end of the 19th century. They also used weather records and computer simulations. At the time of heavy rains, the soil was already partially saturated. Some parts of the valley are very narrow and have steep slopes, which leads to funnel-like effects in case of severe flooding. These factors have also been locally modified by differences in land cover, infrastructure and water management, thus mitigating or exacerbating the devastating effects of severe floods. According to preliminary data, the flood on the Ahar River is estimated to be 500 years or less.

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The floods killed at least 184 people in Germany and 38 in Belgium and caused extensive damage to infrastructure, including homes, highways, railways and bridges, as well as major sources of income. Due to road closures, some places were inaccessible for several days, cutting off some villages from evacuation routes and emergency measures. The most affected areas were the Ahr, Erft and Maas rivers.

Forty-eight scientists from Germany, Belgium, the Netherlands, Switzerland, France, the United States, and the United Kingdom worked together to assess the extent to which human-made climate change would affect the likelihood and intensity of heavy rainfall that led to severe flooding. Using published and peer-reviewed methods, researchers analyzed how man-made climate change affected the one- and two-day precipitation events in the summer season (April-September) in two small regions where recent floods were most severe, namely in the Ahr-Erft region ( Germany) and in the Maas region (Belgium), as well as in a larger region that includes Germany, Belgium and the Netherlands.

The researchers’ main findings

  • “Severe flooding was caused by heavy rainfall over a period of one to two days, wet conditions prior to the event, and local hydrological factors. While river run-off and water levels are the physical components most closely associated with the impact of the event, we focus our assessment on the most important meteorological factor, namely This is heavy rainfall.This is due to the fact that some hydrological monitoring systems were destroyed during the flood and data of sufficient quality and quantity are currently not available.
  • The observed amounts of precipitation in Ahr/Erft and in the Belgian part of the Meuse catchment area exceeded historically observed rainfall records several times. In regions of this size, robust estimation of return values ​​and identification and assignment of trends is challenging and thus reaches the limits of what current methods for mapping extreme events are designed for.
  • Therefore, we extended the analysis by examining the impact of climate change on similar types of events that could occur anywhere in Western Europe in a large area between the north of the Alps and the Netherlands. We found that under current climatic conditions at a given site within this larger region, such an event could be expected on average every 400 years. It also means that we expect such events to occur within the larger Western European region more than once every 400 years.
  • Due to climate change, the intensity of the maximum one-day precipitation in the summer season in this large region has increased by about 3 to 19% compared to the global climate which is 1.2°C cooler than today. The increase is similar to the two-day event.
  • The probability of such an event occurring today compared to a 1.2°C cooler climate increased by a factor of 1.2 to 9 for the one-day event in the greater region. The increase is similar to the two-day event.
    These figures are based on an assessment that includes observations, regional climate models, and high-resolution climate models that directly simulate convection. Changes in intensity and probability are greater in the observational recording than in any of the models.
  • In a climate 2°C warmer than pre-industrial times, models suggest that the intensity of a one-day event will increase by an additional 0.8 to 6% and the probability of 1.2 to 1.4 will increase. The increase is similar to the two-day event.
  • The July 2021 floods had severe effects, including more than two hundred deaths. Given the rarity of the event, it is clear that it is a very extreme event that is likely to have a negative impact. However, since such events will occur frequently in the future, it is critical to study how to reduce sensitivity and exposure in order to minimize future effects.
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in summary Our results show that detection of trends in intense precipitation at the local level is hampered by variability. However, looking at such events that occur in the greater region of Western Europe reveals important trends attributable to man-made climate change, although we cannot predict exactly where these events will occur. All available data taken together, including physical understanding, observations over a larger area, and different regional climate models, give a high level of confidence that human-caused climate change has increased the likelihood and severity of such an event, and that these changes will persist. In a rapidly warming climate. “

Under current climatic conditions, the analysis indicates that a certain region in Western Europe is expected to experience similar extreme weather events approximately once every 400 years. This means that many such events can be expected across the region including France, West Germany, Eastern Belgium, the Netherlands, Luxembourg and northern Switzerland during this period. With more greenhouse gas emissions and another increase in temperature, heavy rain events will occur more frequently.

Political responsibility?

subordinate Deutschland Funk asks in feature (“Study shows the connection – climate change, floods on Ahr and Erft – and the question of guiltCan the current or previous federal government be held responsible for, for example, the storm deaths in the Arctic Valley? Because they failed to act to reduce greenhouse gas emissions earlier? The central question is whether the disaster can be attributed to the phenomenon Global warming or not Attorney Rhoda Verhein at Deutschlandfunk. By studying the WWA attribution, this has now been answered for the Ahr Valley and other regions in Western Europe. According to the latest report from the Intergovernmental Panel on Climate Change (, Western and Central Europe will experience more rain and flooding when temperatures rise.

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However, according to Verhein, the courts have so far been very keen to pinpoint the mistakes of the past. In its April 2021 ruling, the Federal Constitutional Court also found that he had not breached duty by the federal government in the past. Previously, courts in the United States did not allow similar measures and failed due to the resolution of applications. The lawyer stressed that every government in the world must realize that the closer the chain of scientific evidence, the more reluctance to protect the climate will also go wrong. In April 2021, she led the climate case against the federal government before the Federal Constitutional Court (

Then the federal government introduced a new climate protection law. Looking into the future, according to attorney Verheen, this increases the chances of those affected to take legal action. From her point of view, she said in dart.

In more than 400 studies, the academy has now looked at whether the likelihood of extreme weather events has been increased by climate change. Another study by the same scientists who did the current study showed that large heat waves in Siberia last year and Australian bushfires in 2019/2020 were caused in part by climate change. The recent heat wave in North America is unlikely to occur without climate change. But climate change has also increased the possibility of a cold snap that led to the loss of France’s grape harvest.

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