Rains that are desired and more and more scorching days.

Then dry lands and fires, however of human origin, which spread dangerously.

For several weeks, France has been experiencing one of its darkest summers.

The reason: a particularly hot and dry month of July.

But not only…

Is global warming the cause of heat waves?

It's a fact, each additional degree on the thermometer, due to human activities responsible for increasing greenhouse gas emissions, makes heat extremes more frequent and more severe.

Global warming is now +1.1°C compared to pre-industrial levels (1850 to 1900), and +1.7°C in France.

An increase which, in certain regions, has contributed to an intensification of agricultural and ecological droughts linked to soil humidity, due to an increase in evapotranspiration*.

The vegetation is therefore increasingly thirsty, with precipitation being totally unbalanced, insufficient or even absent for several months, then intense over shorter periods.

Global warming, induced by the use of fossil fuels by man (oil, gas and coal) is therefore responsible for the increase in the number of heat waves.

It's getting hotter, longer and longer, and that's not good news.

Climate change, meteorological conditions conducive to fires, risks of forest fires: what is the state of knowledge provided by the IPCC reports of 2021 and 2022 @IPCC_CH and the @hc_climat of 2022?



⬇️🧵


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— Dr. Valérie Masson-Delmotte (@valmasdel) July 16, 2022

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Do heat waves and drought promote the spread of fires?

The intensification of weather conditions is conducive to the outbreak and persistence of fires.

Although fire starts are sometimes caused by recklessness (five times out of ten) or are sometimes intentional (three times out of ten), they are then largely fueled by rising temperatures and the resulting drought.

As in Gironde, Gard and Brittany, at the end of July, or in Dordogne in recent days, among others.

The lack of winter and then spring rains also undermined the water reserves of the soil, already depleted by years of chemical abuse.

Result: after the heat wave, and while fires are still raging in the south of France, the drought is added to the ills of the climate.

What impact on the forests of France and their capacity to store greenhouse gas emissions?

Who says drier atmosphere and environment, necessarily says increased water shortage (also called water stress), with the effect of higher tree mortality and forest decline, which increases the risk of fires.

The vegetation is thirsty!

And it is being challenged by successive heat waves, wind speeds and dry conditions of the previous months, which increase the potential for large forest fires.

In France, the forest carbon sink has declined sharply over the past decade due to land reallocation and increased concreting, although a reforestation plan has been put on the table in the "France relaunch” of the Philippe government in July 2021. The High Council for the Climate had also already pointed out the drop in the storage capacity of carbon emissions by the forests of France: only 30.7 million tonnes (Mt) of equivalent CO2 while the scenarios of the National Low Carbon Strategy emitted by the government had estimated it at 39 Mt. It had however doubled between 1990 and 2000, going from 25 to 50 Mt of CO2 equivalent...

(*) Evapotranspiration corresponds to the emission of water vapor into the atmosphere from the ground and the surface of plants.

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