Heavy rainfall more frequent in southern Germany due to climate change
Bayern and Baden-Württemberg have recently been hit by record-breaking rainfall. With each of these extreme weather events, the question arises: Is it also due to climate change? The German Weather Service compares historical data for this and comes to a clear conclusion.
The likelihood of such heavy rainfall as at the end of May and beginning of June in South Germany is, according to an analysis, already significantly increased in the context of the climate crisis. Instead of occurring on average once every 42 years, as it used to be, such rainfall events are now estimated to occur approximately every 30 years in the region, according to the Regional Climate Office Potsdam of the German Weather Service (DWD).
In a globally two-degree warmer future, comparable events in the region are expected to occur on average every 23 to 25 years. However, the uncertainties in these calculations are quite large.
Heavy rainfall caused flooding and landslides in South Germany between May 30 and June 3. Record rainfall was measured in Bayern and Baden-Württemberg.
Looking Back for Comparison
The scientists of the weather service focused on the catchment areas of the Neckar and Danube rivers, where the strongest rainfall was measured, in their so-called attribution study. The analysis showed that climate change has increased the likelihood of such or stronger rainfall events by a factor of approximately 1.4 (a range of 0.8 to 4.4).
Such an event could occur today significantly more frequently than in a 1.2-degree cooler climate, as it was around the year 1900. The calculations also suggest that the intensity of such a rainfall event has increased in this region by about four percent. "Such an event brings about four millimeters (liters per square meter) more rainfall today than in a 1.2-degree cooler climate," it was stated.
Water in Warm Air
Rising temperatures could theoretically lead to an intensification of rainfall, as explained in the study. The water-absorbing capacity of the air for water vapor increases with rising temperature. "This increased water-absorbing capacity, combined with stronger evaporation over warmer sea surface temperatures, leads to more moisture being taken up in the air over the sea." When these air masses then pass over the continents, they could potentially release more water. "The potential for heavy rainfall therefore increases fundamentally due to climate change."
For an attribution study, meteorological data from the past decades and climate simulations are statistically evaluated. At the beginning of the month, the research consortium Climameter had already presented a similar analysis on the events in South Germany. According to this, the rain that caused the flooding was up to 10 percent stronger than without human-induced warming.
Even apparently small amounts of enhanced precipitation can have disproportionately large effects, as the consortium explained. For example, the Ahr Valley flood of 2021 was reportedly intensified by climate change by 3 to 19 percent.
- The German Weather Service's attribution study in South Germany's flood-affected regions, such as the Neckar and Danube river catchments, indicates that climate change has increased the likelihood of such or stronger rainfall events by approximately 1.4 times.
- In a 1.2-degree cooler climate, comparable events as the one that caused the flooding in May-June 2023, could occur significantly less frequently than they do now, according to the analyses.
- As global warming increases, the potential for heavy rainfall in Germany, like the one that led to the flooding in Baden-Württemberg and Bayaria, could increase fundamentally due to the enhanced water-absorbing capacity of air for water vapor and stronger evaporation over warmer sea surface temperatures.
- In light of the increased likelihood of extreme weather events due to climate change, it's crucial to incorporate education about meteorology and climate change into school curricula to ensure a more informed public and better preparedness for future events.
