The study is the latest in the growing field of rapid attribution science, which examines extreme weather events like downpours and heat waves to see whether they were influenced by climate change, and if so, to what extent. It was conducted by World Weather Attribution, a collaboration among climate scientists and others.
The studies are performed quickly, while the event is still in the public’s mind. The speed usually means that the studies are not peer-reviewed until later, but they use peer-reviewed techniques of analysis, incorporating models and observational data.
The flooding study comes with some caveats, the researchers said. By itself, rainfall doesn’t tell the whole story of a flood; river flow rates and water levels are better indicators of a storm’s eventual impact. But the flooding destroyed many instruments that would have provided that data, “so we focused our assessment on heavy rainfall as the main driver,” said Sarah Kew, a climate scientist with the Royal Dutch Meteorological Institute.
The rainstorms occurred over two relatively small areas, too small to be represented in many climate models. So the researchers used a “pooled regions” approach, including other areas from north of the Alps to the Netherlands.
Despite these limitations, “we still are quite confident that the results we provide are quite useful,” said Frank Kreienkamp, a climate scientist with the German Meteorological Service.
The low end of the range of outcomes — that warming made such a rain event 1.2 times more likely — suggests that climate change had less of an influence and that the event was more a result of natural climate variability. But even that figure represents an increase in likelihood of 20 percent attributable to climate change, which is significant, Dr. Kew said.
The research was made public two weeks after the publication of a major United Nations report on climate change, which found, among other things, that extreme weather events will continue to increase in frequency and magnitude as warming continues.
