In the immediate wake of a weather disaster, people like to wonder whether climate change is partly to blame for the disaster's severity. The problem is that any meaningful, serious answer to that question takes time—so much time that public attention has moved on before we get an answer.

For one group of climate scientists, that unfortunate problem sounded more like a challenge. With a good plan and the right setup, the team figured it could quickly run the necessary climate model simulations and spit out some basic results. By comparing a virtual world where humans didn’t drive up concentrations of greenhouse gases to the one we live in, the models can be used to see whether there's any change in the weather patterns associated with the latest disaster.

At the end of May, the team got a chance to take its system for a test drive. Weather linked to a lingering low pressure system dumped rain on France and Germany. Three days of steadily heavy rain, following a wet spring, caused flooding on the Seine and Loing rivers upstream of Paris. In Paris, the water level in the Seine rose more than 6 meters (over 20 feet), prompting the evacuation of art from basement levels of the Louvre. In other areas, thousands of human beings were evacuated as well.

In Germany, the damage came from flash flooding associated with intense rains produced by severe thunderstorms on May 29 and 30. The town of Gundelsheim, for example, saw more than 12 centimeters (almost 5 inches) of rain in less than a day. Radar estimates picked up a peak rate of around 9 centimeters (3.5 inches) per hour near Braunsbach, where cars were washed away.

The researchers utilized a cache of simulations run previously with several different climate models, including one run with spare CPU time from the volunteers of the weather@home network. In each case, multiple simulations of worlds with and without climate change were combined to calculate statistical probabilities of extreme rainfall events—three-day rains over northeastern France and one-day rainfall over southwestern Germany.

In contrast to the months or years it has taken in the past, the team actually had results out in less than a week ready to share with the media. A week later they had the paper, which the authors shared with Ars. It has since been submitted for open peer review in the journal Hydrology and Earth System Sciences, where it appeared Wednesday.

In France, the timing of the flooding was pretty unusual. The highest historical flood levels in Paris have all come in winter rather than late spring. As far as three-day rain totals in spring, this would only be expected to occur once every few centuries—although rainfalls in other portions of the area were only about 50-year events. These rare events were about twice as likely to occur in the simulations with greenhouse-gas-driven global warming. Another way to put that: a 100-year rain is now about 6 percent heavier than it was before.

For southwestern Germany, the study didn’t reveal much. Available records show that extreme one-day rains at this time of year have actually become less common over the past 50 years. Because the thunderstorms responsible depend on small-scale processes, most of the models did a poor job simulating them. The model that did best at the thunderstorms simulated an increase in this type of rainfall, though. The researchers would have to look more closely to figure out what to make of that.

So was climate change partly to blame for the severity of the flooding in France and Germany a few weeks ago? According to this incredibly quick analysis, the answer for France is “probably” and the answer for Germany is “we don’t know.” There may be further research on this—and the details of this study may even evolve somewhat as it goes through the peer review process—but a scientific answer was available before the ground had even dried out. You can expect to see that more often in the future.

Under review at Hydrology and Earth System Sciences, 2016. DOI: 10.5194/hess-2016-308 (About DOIs).