Scientists: Climate change contributes to heavy rain


After the long and heavy rains in the middle of the week, more and more catastrophic consequences are becoming apparent: The number of deaths is growing, over 100 people have died in Rhineland-Palatinate and North Rhine-Westphalia alone. Many houses collapsed or were washed away. The infrastructure is battered, and in some places neither electricity nor telephones work. Bridges damaged or swept away by the floods. The Science Media Center asked scientists about the connection with climate change.

“In 2021 the question no longer arises as to whether climate change has contributed to this. The only question is how much,” emphasizes Carl-Friedrich Schleussner, group leader at the Geographical Institute at the Humboldt University in Berlin. “We know that the warming will lead to an increase in heavy rain and, unfortunately, to more frequent, devastating flood events, as tragically now in West Germany, Belgium and Luxembourg.” At the same time, weather conditions that led to such events are increasing.

Attribution research can meanwhile point out in many cases for heat and heavy rain“That the probability of such events occurring, as well as often the intensity of such events, increases due to climate change,” says the Swiss climate physicist Sebastian Sippel. “For every one degree Celsius increase in temperature, the atmosphere can absorb around seven percent more moisture.”

Douglas Maraun, head of the Regional Climate Research Group at the University of Graz, estimates that climate change has “increased the recent rainfall by 10 to 20 percent”. The research describes the strength of an extreme event through the annuality: The sewer system is designed for annualities of a few years, a dam should withstand a 100-year event, a nuclear power plant a 10,000-year event.

“For many parameters, the current event was outside of any previous observations,” say Christian Grams and Julian Quinting from the Institute for Meteorology and Climate Research in Eggenstein-Leopoldshafen: Deep “Bernd” was wedged in and brought warm Mediterranean air back from the North Sea and Eastern Europe Led south, where it rose above the cooler air mass. This has led to the massive amounts of precipitation. The soils were already saturated and the highly indented terrain with partly deep river valleys increased the surface runoff.

Another much-discussed effect is that Weakening of the summer circulation of the atmospherethat ensure long-lasting weather conditions, explains Stefan Rahmstorf, professor at the Potsdam Institute for Climate Impact Research. “A few hot days turn into a heat wave, a ‘stuck’ low leads to continuous rain.” That has to do with the fact that the Arctic has warmed three times as much as the rest of the earth in the past few decades.

“Conventional urban water management and hydraulic engineering design approaches are not sufficient to effectively protect the infrastructure against such extreme events,” explains Boris Lehmann, holder of the Chair of Hydraulic Engineering at the TU Darmstadt. But it is not possible to rebuild and secure “all elements of our cultural landscapes and infrastructure”. It is therefore important “in potentially endangered areas by using simulation tools to first examine where the system-related ‘bottlenecks’ and potential for damage are”.

Christian Kuhlicke, head of the Extreme Events working group at the Helmholtz Center for Environmental Research in Leipzig, called for the aging infrastructure to be “future-proofed over the next five to ten years”. Electricity and communication networks have to be designed in such a way “that they also work in extreme locations”. The reconstruction in the affected parts of the country offers the possibility of “setting new standards for the future”. Villages, cities and landscapes should be designed like sponges. Nature-based solutions are green roofs, better infiltration options in open areas and decentralized storage options in near-natural retention zones.