Climate change has made summer drought “at least 20 times more likely”

DAMIEN MEYER / AFP This photo taken in Loireauxence in western France on September 20, 2022 shows a bridge over the drained bed of the Loire River. – This summer was the second hottest ever recorded in France with average temperatures of 2.3 ° C above normal, a series of large-scale fires that devastated much of the southwest and widespread drought, as well as several severe storms. (Photo by Damien MEYER / AFP)


A bridge over the dry bed of the Loire, in Loireauxence (Loire-Atlantique), 20 September 2022.

ENVIRONMENT – Climate change caused by human activity has dried up the Northern Hemisphere this summer “at least 20 times more likely”and continued warming would make these episodes more intense and more frequent, scientists warn.

Such a soil drought, which has affected Europe, China or the United States, is likely to occur roughly every 20 years with the current climate, versus roughly every 400 years or even less often without warming, according to researchers from World Weather Attribution (WWA), a network of researchers pioneering the attribution of extreme events to climate change, which will publish a study on Wednesday 5 October.

Summer drought has affected many European countries, starting with France, with dry rivers and restrictions in some locations. Parts of the United States or China were also affected.

The consequences were felt in the agricultural sector, with declining harvests and possible effects on already high inflation. This situation has also favored forest fires and disrupted the production of electricity, especially hydraulics and nuclear power.

Experts from the European Commission’s Joint Research Center estimated this summer what a drought was “The worst in at least 500 years”.

In the Northern Hemisphere (outside the tropics), human-induced climate change has resulted in drought “ much more likely “according to researchers from the WWA network, who work at prestigious institutions in Europe, the United States and New Zealand.

This probability has been increased by one factor “At least 20” due to the lack of soil moisture in the root zone, the part of the ground corresponding to 1 meter underground and where the plants extract water to feed. It is when this very important area is hit that we speak of “agricultural” drought. Where is it “ecological”.

The probability of the event was increased by one factor “at least 5” for surface soil moisture, which is only the first seven centimeters.

Warming since the beginning of the industrial era has already reached almost 1.2 ° C

“But as usually happens with quantities that are difficult to observe, the exact numbers are uncertain”the authors warn. “Estimates of the influence of climate change in the study are conservative: the true influence of human activities is likely to be greater.”states the WWA.

Warming since the beginning of the industrial era, which has been fueled by fossil fuels, has already reached almost 1.2 ° C, causing a series of disasters. The Paris Agreement aims to keep this warming below 2 ° and if possible close to 1.5 °.

“The summer of 2022 showed how man-made climate change is increasing the risk of agricultural and ecological drought in the agricultural and densely populated regions of the Northern Hemisphere.”stressed Sonia Seneviratne, professor in Zurich, co-author of the study.

“We must stop burning fossil fuels if we want to stabilize the climatic conditions and prevent these droughts from worsening. They will become more frequent and intense with any increase in warming. “he warned.

The researchers also looked at the central and western European region alone. The results are less spectacular: human-related global warming made surface drought 5 to 6 times more likely there and agricultural drought 3 to 4 times more likely, according to their calculations.

This difference does not mean that climate change has had less impact on Europe than the rest of the Northern Hemisphere, but rather reflects the methodological ease of a better understanding of events in a wider region.

“We usually get stronger signals about climate change over larger regions”Friederike Otto, of Imperial College London, co-author of the study, explained during a presentation to reporters.

“When you look at smaller regions, you find greater daily weather variability in the data”while this effect is “attenuated” taking larger areas into account, he explained.

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