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

DAMIEN MEYER / AFP This image, taken September 20, 2022 in Loireauxence, western France, shows a bridge over the dried-up Loire riverbed. – This summer was France’s second-warmest on record, with average temperatures 2.3°C above norm, a series of widespread wildfires that ravaged much of the south-west and a widespread drought along with several severe storms. (Photo by Damien MEYER / AFP)


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

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

Such a soil drought, which has affected Europe, China or the United States, is likely to occur about every 20 years in the current climate, against about every 400 years or even less frequently without warming, according to researchers from the World Weather Attribution (WWA), a network of pioneering researchers in the attribution of extreme events to climate change, releasing a study this Wednesday, October 5.

The summer drought has hit many European countries, starting with France, with dried up rivers and restrictions in some places. Parts of the USA and China were also affected.

The fallout was felt in the agricultural sector, with declining harvests and a possible impact on already high inflation. This situation has also encouraged wildfires and disrupted power generation, particularly hydroelectric and nuclear.

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

In the northern hemisphere (outside the tropics), human-caused climate change has led to droughts. much more likely”according to researchers from the WWA network working at renowned institutions in Europe, the United States and New Zealand.

This probability has been increased by a factor “at least 20” for the lack of soil moisture in the root zone, the part of the soil corresponding to 1 meter below the ground and where the plants draw water to feed themselves. When this very important area is affected, it is called an “agricultural” drought. Where “ecologically”.

The probability of the event has been increased by a factor “at least 5” for surface soil moisture, which is only the top seven centimeters.

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

“But as is usual with hard-to-observe quantities, the exact numbers are uncertain”the authors warn. “The estimates of the impact of climate change in the study are conservative: the true impact of human activities is likely higher”says the WWA.

Warming since the start of the fossil fuel-driven industrial age has already reached almost 1.2°C and has led to a series of catastrophes. The Paris Agreement aims to keep this warming below 2° and as close as possible to 1.5°.

“The summer of 2022 has demonstrated how human-caused climate change increases the risk of agricultural and environmental droughts in agricultural and densely populated regions of the Northern Hemisphere”underlined Sonia Seneviratne, professor in Zurich, who co-authored the study.

“We must stop burning fossil fuels if we are to stabilize climatic conditions and prevent these droughts from getting worse. They will become more frequent and intense with any increase in warming.”she warned.

The researchers also only looked at the Central and Western Europe region. The results are less spectacular: Global warming associated with human activities has made surface droughts about 5 to 6 times more likely and agricultural droughts about 3 to 4 times more likely, according to their calculations.

This difference does not mean that climate change has had less of an impact on Europe compared to the rest of the northern hemisphere, but rather reflects the methodological ease of gaining a better understanding of what is happening in a larger region.

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

“If you look at smaller regions, you’ll find more diurnal weather variability in the data”while this effect is “muted” considering larger areas, she explained.

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