Cold and frost: an alarming situation for the agricultural sector

TO Cyril BONNEFOY, meteorologist

After a period of softness worthy of May, the winter chill returns this weekend and brings back bad memories of yesteryear. Farmers are especially wary of the second scenario of 2021, when late frosts caused significant damage to some orchards, vineyards or vegetable gardens. So what can you expect in the coming days? Could the risk of a typical 2021 scenario repeat itself?

Farmers are especially afraid of the beginning of spring because it is a period of extremes. This week’s weather will be another example as we will drastically change from spring to winter in 48 hours. Vegetation, which may have begun in recent weeks, will be particularly at risk of frost.

Increasingly early start of the growing season

History seems to be repeating itself in recent years and may find its source in our climate change. Indeed, there is a trend towards milder winters than before, with actually an earlier growing season in late winter and early spring. In viticulture, for example, the date of bud break (the emergence of buds from the cocoon) is on average 2-3 weeks ahead of what it was 30 years ago, which is not without consequences. Instead of starting in April, vineyards now start harvesting in March, a month during which frost risk is statistically much higher, even in the context of climate change.

A series of dark years: 2017, 2019, 2021

When a new polar air release is scheduled for this weekend, it brings back bad memories of the last few years, starting in 2021. After all, last year was especially catastrophic for our farmers (see our article about this). After an exceptionally mild period at the end of March, the descent of polar air caused a drop in temperature between 5 and 8 April. Many of the cities that broke records for mildness, even heat on March 30 and 31, broke records for cold in early April. Beauvais, for example, went from a soft record (24.8°C) to a cold record (-6.9°C) in a matter of days. Agricultural losses were significant, sometimes all wineries were affected, and no region could avoid it. This episode, with serious consequences for farmers, follows already two gloomy years due to frost: 2017 and 2019. We understand that they are following the forecasts for the coming days with concern and are again preparing for difficult days.

Temperature drop at the end of the week: what to expect?

This drop will occur in two stages: the first drop will occur this Wednesday, and the second, more significant, will occur at the end of the week. On Wednesday, you’ll find temperatures closer to normal for the season, or even lower in the north of the Loire. In Paris, maximum temperatures will drop from 18°C ​​on Tuesday afternoon to just 11°C on Wednesday afternoon, 3°C below normal. It will still be fairly mild in the south, but a second, more substantial drop is expected between Thursday and Friday. We will return 5-10°C below seasonal norm across the country. This second drop in temperature will be caused by a depression that will slide from north to south and lift the polar air with it. We follow the risk snow episode between the Hauts-de-France and the center of the country via the Île-de-France, even if there are still many uncertainties at present.

Weekend under the close supervision of agriculture

Frost risk for vegetation should start especially this weekend as the skies clear behind the depression. On Saturday, the northwestern regions seem to be most at risk of frost, while on Sunday and Monday the risk will extend to 3/4 of the country. Where the clearings will break through, frosts may well be severe for some models, with down to -5°C on the plains and -10°C near the Vosges and Massif Central. At this deadline, it is difficult to be more precise, but the potential is there and there are fears of significant damage to already well-developed vegetation.

Which regions are most at risk today?

Fruit trees have already begun to grow a few weeks ago in most tree regions, aided by the mild period we have just gone through. Therefore, they will be especially susceptible to frost. Foresters, unfortunately, have to prepare for heavy losses in some operations. For viticulture, the risk is higher in the Burgundy region, where the vine leads 7 to 15 days. In Bordeaux, the vine is quite late, which is a more favorable situation than last year, but except for sites cut late, all others must reach the cotton bud stage, so the risk will not be zero. The Departmental Federation of Trade Unions of Agricultural Exploiters of the Gironde (FDSEA 33) also recommends that the winegrowers of the department protect themselves from this weekend, anticipating the implementation anti-freeze agents.

Another problem for the sector is the presence of moisture in the air and on the ground due to precipitation on Thursday and Friday. Water that seeps into the buds can cause them to pop much more easily when it freezes. Finally, possible snow on the ground in some regions, such as Burgundy-Franche-Comté and Center-Val-de-Loire, could contribute to nighttime radiation, increase frost and increase potential crop damage.

After such a particularly mild start to spring, winter is back in full force this weekend. Farmers are preparing to limit their losses after a series of bad years. If this episode of significant cold for the season is received, the situation will need to be further clarified due to uncertainties associated with some parameters such as cloudiness and snowfall. We will return to this in our next updates.

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