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Tractor on a dry potato field: Dangerous combination of extreme drought and heat
Photo: Jochen Eckel / imago images
With the advancing climate change, more and more severe weather extremes are to be expected in Germany.
"We all have to prepare for this early on," said Tobias Fuchs from the board of the German Weather Service (DWD) on Wednesday at the opening of the 10th Extreme Weather Congress in Hamburg.
Heat waves would increase in the future.
"The rise in temperature in Germany is accelerating."
Since the beginning of systematic, area-wide weather records in 1881, the mean temperature in Germany has risen significantly.
According to DWD data, the current decade is around 1.9 degrees warmer than the first decades of records from 1881-1910.
According to a paper on the state of science published at the congress, there will continue to be cold winters, cool summers and the risk of late frosts within the framework of natural fluctuations.
However, the probability of these events is decreasing as a result of global warming.
"Winter is getting shorter, spring and autumn are getting longer."
"It is important to understand that not all extreme weather events occur more frequently," said the chairman of the German Climate Consortium, Mojib Latif.
"For example, we are seeing a decrease in severe frosts and no increase in storms in northern Germany."
Fuchs further reported: "What used to be very extreme summers, in the thirties / forties, now falls into the area of normal summers. Winter is getting shorter, spring and autumn are getting longer."
In some areas of Germany, long periods with maximum daily temperatures of 30 degrees and little rain are a new phenomenon.
The drought is therefore causing problems - with consequences for forests and agriculture.
The chairman of the World Meteorological Organization, Gerhard Adrian, called for more climate protection via a video message: "Worldwide, more and more people are directly affected by climate change," he said.
"All the important levers are still turning in the wrong direction."
The greenhouse gas concentration in the atmosphere is still increasing.
"Corona will hardly have any effect."
In the USA the risk of severe droughts increases
Shortly after the meeting, a study was published in the journal "Science Advances" on Wednesday, according to which the risk of persistent mega-droughts in the USA is significantly increasing due to climate change.
According to the researchers, this favors violent forest fires, as can currently be observed.
Climate change could lead to droughts lasting for decades, write researchers working with Mohammad Reza Alizadeh from McGill University and Mojtaba Sadegh from Boise State University.
Such long dry phases also existed in the USA in the 12th and 13th centuries.
However, global warming has increased the risk again.
As climate change progresses, it is more common for extreme events like heat waves and drought to occur at the same time, the researchers said.
Her study focuses on this drought and heat coexistence over the past 122 years.
"Episodes of extreme drought and heat are the recipe for large forest fires," said Mojtaba Sadegh.
"These extremes are intensifying and expanding to unprecedented spatial proportions, making the current forest fires possible along the entire US west coast."
Dozens of fires have raged there since mid-August.
In California alone, around 19,000 emergency services fought more than two dozen major fires.
The flames have destroyed more than 5,800 buildings since mid-August.
Even shorter periods of drought that lasted less than a decade, such as the US drought known as the "Dust Bowl" in the 1930s, could have devastating effects if coexisted with heat.
Among other things, climatic events in the atmosphere and on the ground in their interaction could lead to such extremes, according to the study.
Dangerous interaction
The scientists suspect that the main driving factor behind simultaneous heat and drought periods in the recent past is excessive heat.
In the "Dust Bowl" period, however, a lack of precipitation was the main trigger.
A mega-drought is usually preceded by a long high-pressure area, creating cloudless conditions that allow hot air to enter.
Dry soils increase the proportion of heat in the incoming sun rays, which affects the ambient temperature, according to the article.
This has the consequence that heat waves intensify.
As an example, the researchers cite the heat wave in Russia in 2010. There, the probability of a mega heat wave increased by a factor of 13 due to the interaction of drought and heat.
The interplay of dry soil and hot air prevents clouds from forming, which means less rain and, as a result, intensifies the drought.
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jme / dpa