Our planet is warming up – the consequences are serious. Heat waves are only one aspect. Global warming also has an impact on the frequency of heavy rain events.
Dead and missing, collapsed houses and flooded cities – western Germany is experiencing extreme rainfall. In view of the ongoing climate change, the question arises: Will such catastrophes affect Germany more frequently in the future? The most important answers.
What weather conditions has currently led to the floods?
The German Weather Service justifies the current weather situation with the fact that a low pressure area over western Germany has ‘seized up’. The low is flanked on all sides by high pressure areas, so the extremely humid air cannot escape, explains DWD meteorologist Marco Manitta. “Such weather conditions have become more common in recent years,” says Manitta. In the opposite case – when a high is ‘surrounded’ by lows – extreme heat and drought occur.
According to Manitta, the greatest amounts of precipitation occurred in a wide strip from the Sauerland over the Bergisches Land and the Eifel, the greater Cologne / Bonn area to the border with Luxembourg. The front runner was Rheinbach-Todenfeld (Rhein-Sieg-Kreis in North Rhine-Westphalia) with 158 liters per square meter in 24 hours – most of which fell from the sky in a shorter period of time, as the expert explained.
What does global warming have to do with it?
Two effects of global warming influence the frequency of such extreme heavy rain events, says Peter Hoffmann from the Potsdam Institute for Climate Impact Research: On the one hand, more water evaporates at higher temperatures and the warmer atmosphere can store more moisture. This favors high amounts of precipitation.
On the other hand, weather conditions persist longer over a region. Behind this is a global phenomenon: the atmosphere does not heat up evenly, but more at the poles than at the equator. This reduces the large temperature difference between these two regions. The result: the so-called jet stream, which moves as a band of wind around the northern hemisphere at great heights, is changing.
This means that weather conditions can stay in one place for a long time and create extreme conditions. “The problem is not the weather itself, but that it persists for a long time,” says Hoffmann.
Is it raining more in this country due to global warming?
According to the National Climate Report, precipitation is subject to strong fluctuations from year to year. The average annual rainfall in Germany has increased by 66 millimeters since 1881 – or by eight percent compared to the reference period 1961 to 1990. This is not a continuous increase: ‘The increase was uneven.’ In addition, the increase is ‘superimposed by short-term fluctuations’.
The extreme precipitation is actually more conspicuous in a different season: ‘The winter precipitation has increased since the winter of 1881/82 until today by 48 millimeters or 26 percent relative to 1961-90,’ says the climate report.
Even if the total amount of rain in Germany has changed little in the past few decades, something has changed, as climatologist Hoffmann explains. There are indications that the same amount of rain comes from the sky on fewer days of the year: ‘When the rain falls, it is more intense’.
Is it not raining any more due to climate change, but more?
According to the Federal Environment Agency (UBA), it has not yet been possible to “make statistically reliable climatological statements about changes in heavy precipitation events”. It is different with the temperature: It has been proven that the frequency of hot days has increased throughout Germany. ‘It is more difficult to make reliable statements about trends in heavy precipitation events.’ However, the UBA definitely sees ‘tendencies towards a greater frequency of heavy precipitation in the last 65 years’.
Climate models give a very clear picture that heavy rain days are increasing in Germany, says Hoffmann. ‘It is unclear to what extent.’ The data on this is still somewhat limited. Using radar data, however, one can also see that no region is particularly affected. Heavy rain days are in themselves rather rare events. Depending on the region in Germany, it can only be three or ten per year.
In relation to extreme situations like now in western Germany, it makes a big difference whether there are half an extra day of heavy rain a year due to climate change, says Hoffmann. The German Weather Service (DWD) speaks of heavy rain when, for example, more than 15 liters per hour and square meter come down from the sky.
When does heavy rain become a problem?
Heavy rain becomes a problem wherever the water cannot run off. ‘The less space the water has, the more damage you have to expect,’ says PIK expert Hoffmann. This applies to geological locations such as in mountains, but above all to cities. ‘We are making the flood risk worse by sealing more and more areas,’ says geographer Matthias Garschagen from the Ludwig Maximilians University in Munich. Urban planning must adapt to climate change.
Once the catastrophe damage has been cleared up in the Eifel and other regions currently affected, ‘then we mustn’t wait for the next disaster,’ warns Garschagen, ‘then we have to tackle it: there are big tasks ahead of us.’ The municipalities would have to strengthen flood protection, homeowners had better provisions, and politicians would have to discuss who bears the costs.
Do we now experience such extreme weather situations more often?
‘Even small changes in the global average temperature can have a major impact on the increase in extreme weather events,’ says Garschagen. The probability of heavy rain or drought increases disproportionately with every further degree of temperature increase. ‘The question is: how quickly do we manage to deal with it?’
Climate activist Greta Thunberg wrote on Twitter: «Deadly heat waves, floods, storms, forest fires, droughts, crop failures … this is not ‘the new normal’. We are at the very beginning of a climatic and ecological emergency, and extreme weather events will only become more frequent. ‘
