Heat wave: “Disastrous agroclimatic conditions for ecosystems”

This Monday, July 18, 2022, it was 42.6°C in Biscarosse (Landes), 41°C in Niort (Deux-Sèvres), 40.7° in Angers (Maine-et-Loire) and 39.3°C in Brest (Finistère) — it’s more than 4°C warmer than the previous one record heat established in 1945. Unheard of. And it’s not over. The heat continues on its way east.

Such temperatures, we now know, are difficult to bear. Yesterday, Spain and Portugal, which live under the same heat wave than France, reported a total of at least 344 heat-related deaths in one week. But men are not the only ones to suffer from the situation. in full season culturally, it also affects plants and animals. ” The corn slows its growth from 31°Cexplains online Serge Zaka, doctor in agroclimatology. At 40°C, its growth and development simply stop. The conditions we are currently experiencing are disastrous for ecosystems “.

However, it is not directly the heat which really poses a problem. “When such heat wave lasts, it is the water problem that takes precedence over the thermal problem. » Because with the heat, the evapotranspiration increases and in a context of drought marked, the plant’s water index may drop.

Heat and humidity, two parameters to take into account

The livestock experience the same type of difficulties. To assess the risk, scientists rely on an index that takes into account both temperature and relative humidity, the THI index — to Temperature-Humidity Index. “It is a warning indicator”, explains Bertrand Fagoo, from the Livestock Institute (Idele). Thus, for a relative humidity of 30%, for example, the level of stress extreme will be reached from 38°C. For a humidity of 90%, it will be reached from 30°C. in these two situations, a single THI value of 84.

But “the sensitivity is different depending on the speciesspecifies Bertrand Fagoo. Ruminants, for example, produce a lot of heat. They are much more sensitive to hot than to cold. Among them, the cow dairy is the most sensitive. When vague heat last June, “lethal levels have been reached for the first time in France”reported Serge Zaka on his LinkedIn account.

Note, however, that the THI index does not take into account any control measures that may be implemented by farmers. All the more easily when they are alerted upstream. But what are these measures? “Shade in the meadows thanks to treesand shade in the buildingstells us Bertrand Fagoo. But also of ventilation, with open buildings. Without bringing in the Sun . If necessary, we can even add fans. However, this is not enough. A veterinaryreminded him, yesterday, on his account Twitter . Supporting images.

Water at the heart of the fight

You also need water. Lots of water. Because “the dairy cow doubles its needs in hot weather”. So of thefresh water and clean is the best way to help him keep his body at the correct temperature.

The rations must also be adapted. It’s a bit technical, but during a heat wave, scientists advise reducing the level of cellulosein cow feed. During the digestion , in fact, cellulose produces extraheat in large quantities. It is therefore better to concentrate the ration rather in energyand in protein. And distribute it rather in the evening so that it stays fresh longer.

A growing risk with climate change

” With the climate changethe risk will increase”, warns Bertrand Fagoo. For the time being, these measures make it possible, most of the time, to maintain a certain level of well-being and health for ruminants. “But the sector continues to work to adapt. » Some countries warmer than France, Israel for example, already have to resort to much greater resources. ” The mechanical ventilation , showering and buildings open on all four sides. » In the United States, in particular, disasters have occurred. Last June, when the temperatures rose sharply along with the humidity. Thousands of animals perished. “In outdoor feedlots with animals huddled together without shadetells us the expert of Idele. Fortunately, this breeding model does not exist in France”.

Without going to death, “The risks are still real for health and well-being” of our cows. Fatigue, reduced immune defences, metabolic diseases are just a few examples of the inconveniences they may have to face in the event of high temperatures. The problem, too, is that the problems do not stop as soon as the temperatures go down. They extend over time. The longer a heat wave lasts, the longer the recovery time will be.

The effects on milk production can even be felt weeks after the heat wave. Because yes, the consequences for operators also exist. When temperatures rise, milk production decreases. “The quality of production is also falling”, specifies Bertrand Fagoo. Reproduction difficulties appear. On the one hand because the duration and the intensity of the heat of the cow decrease. On the other hand because the thermal stress may cause abnormal embryonic development.

So many more reasons to drastically and urgently reduce our emissionsof greenhouse gas!