How bad is it?

Heavy rain: climate change is a “contributor”

Due to the heavy rainfall, the whole of Lower Austria was declared a disaster area on Sunday.

(Bild: APA/HELMUT FOHRINGER)

Climate change is a kind of "contributor" to the current extreme rainfall. However, the cause is likely to be several factors, such as a combination of a certain meteorological weather situation with cold air and the extremely warm Mediterranean Sea.

The latter is partly due to global warming, explained Douglas Maraun, Head of the Regional Climate Research Group at the Wegener Center for Climate and Global Change in Graz.

In general, a warmer climate leads to more extreme precipitation because warm air can absorb significantly more moisture. "In the current case, this means that the weather situation that is now moving across Central Europe is taking more moisture with it than it might have done 50 years ago. But there are other factors at play at the moment," says Maraun. In addition to the weather situation with a cold snap, the Mediterranean is extremely warm at the moment, which means that significantly more moisture can evaporate.

(Bild: APA/BMLV/DANIEL TRIPPOLT)

Climate change takes full effect thanks to cleaner air
According to the expert, the warming of the Mediterranean is partly due to climate change, but also to the significantly cleaner air over Europe. Due to stricter pollution regulations for shipping, less dirt is released into the air, which means that less sunlight is scattered back into space. This heats things up even more. "Until the mid-1970s, the climate change trend was very much overshadowed by air pollution. Now it is taking full effect because the air over Europe is getting cleaner and cleaner," says Maraun.

Mystery of what triggered the heatwaves
One open question in climate research is what triggered the heatwaves of the past two or three years that led to the warming of the oceans. "Some believe it is a direct result of climate change, some attribute it to air purity. Others see an amplification due to random natural fluctuations," he says, referring to the possible combination of various factors.

In general, the character of precipitation is very much determined by natural fluctuations. "This means, for example, that we have decades in which more such lows pass through, and decades in which fewer pass through. That is the basic tone of natural fluctuations in the climate system. And climate change is now exacerbating this. Droughts are becoming much drier. Heavy rainfall is becoming more intense," says Maraun.

Heavy precipitation will increase
In summer, the number of precipitation days is likely to decrease overall because the atmosphere will stabilize "and we will come under the influence of high pressure more strongly. If we then get thunderstorms in summer, they will be more severe." However, climate change would probably cause the storm tracks to shift further north, which in turn could lead to slightly fewer weather situations like the current ones. But that is not yet certain.

The fact that warmer air can absorb more moisture and that heavy precipitation is expected to increase in many regions of the world is also clearly stated in the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC). The Council is a UN institution based in Geneva. Every five to seven years, experts compile the scientific knowledge on climate change for it. However, there is still surprisingly little research on weather conditions like the current one, says Maraun.