Climate research
Floods are becoming more common with climate change
A swan on a flooded federal highway in Rhineland-Palatinate. photo
© Thomas Frey/dpa
The amount of precipitation in Germany remains roughly the same. However, with climate change, the distribution of water volumes is changing. This means that floods can occur more frequently.
One cause of the current flood is probably the seasonally high surface temperatures of the western Atlantic, which lead to high evaporation and therefore a lot of water vapor in the atmosphere, explains Hattermann. The westerly winds that prevail in our latitudes transported these moist air masses to Europe, where, as a result of a chain of low-pressure areas that moved quickly across Central Europe, there was heavy rainfall in autumn and winter and then floods. “The soils became saturated with water and then hardly absorb any water.” That leads to flooding.
The same amount of water – but distributed differently
The long-term average rainfall in Germany has hardly changed. “There are no strong trends for Germany, but the variability of precipitation is increasing,” says Hattermann. In short: There is heavier rain, but also longer dry periods. According to Hattermann, there are two reasons for this. Firstly, climate change is causing the air to warm up, which can then absorb more water. “The amount of water per cubic meter of air has increased.” This initially means longer dry phases – and when it rains, more water falls on the earth.
Secondly: “We have more stable general weather conditions over Europe.” This is related to the influence of climate change on the jet stream, a wavy air current a few kilometers above the earth’s surface, although the individual connections have not yet been precisely clarified. Such a situation, for example, led to long-lasting high-pressure weather conditions such as those in 2018 and in spring 2023. “A high-pressure area rotates clockwise and brings dry air from the Eurasian region to Germany,” says Hattermann. This leads to little rainfall and drought.
“In 2021 we had a low pressure area where the wind turned counterclockwise and brought moist air from the Mediterranean to Germany.” That led to the water masses in the Ahr Valley in 2021.
According to Hattermann, a longer-lasting weather situation also plays a role in the current flood in Germany, in which the jet stream was over Central Europe and Germany. “The jet stream transported the low pressure areas to us like on a conveyor belt.” The exact proportion of climate change in a single event is difficult to determine. However, such extremes are much more likely due to the higher temperatures and greater evaporation, especially over the oceans, which is also driven by the higher sea surface temperatures.
Current extent “very unusual”
According to the German Weather Service, it has become significantly wetter in this country, especially in winter. “We have known for a long time that climate change leads to more and heavier precipitation in the winter months, which can then be associated with floods,” says the director of the Climate Service Center Germany (Gerics), Daniela Jacob, in an interview with the digital media house Table.Media. “However, the extent of the current flood is very unusual.” This clearly shows how important it is to implement protection strategies quickly and comprehensively.
What to do? “The big issue is of course avoiding further warming,” says Hattermann. However, it is also necessary to adapt the infrastructure and give rivers more space as well as to design the landscape in a climate-adapted manner, such as converting coniferous to deciduous forests. Deciduous forests absorb more water in winter because the snow doesn’t stay there and evaporate from there like it does on conifers.
Every individual should also be aware of the increasing risk: “There is no total protection against flooding,” emphasizes Hattermann. Everyone should know escape routes and, for example, not store valuables in the basement. “We need to create more awareness of the danger and at the same time the knowledge that you cannot protect yourself from everything.”