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?

The beginning of spring remains a particularly scary time for farmers because it is often a time of extremes. The weather this week will again be a great example as we will radically transition from spring to winter in 48 hours. Vegetation, which may have begun in recent weeks, will be particularly at risk of frost.

Increasingly important progress in vegetation care

History seems to want to repeat itself in recent years and may be witnessing the evolution of our climate. Indeed, winters tend to be much milder than they used to be, and therefore earlier vegetation appears in late winter and early spring. Thus, in viticulture, the date of bud break (the emergence of buds from the cocoon) is on average 2–3 weeks ahead of the 1990s, which is not without consequences, since instead of moving away from the vine in April, the latter starts sooner, it’s now March, a month in which frost risk is statistically much higher, even in the context of climate change.

A series of dark years: 2017, 2019, 2021

A new polar air launch scheduled for this weekend brings back bad memories of the last few years, starting in 2021. Indeed, last year was especially disastrous for our farmers. Remember: after an exceptionally warm period at the end of March, the descent of polar air caused a drop in temperature between April 5 and 8. Many of the cities that broke records for mildness, even heat on March 30 and 31, broke records for cold in early April. So it was in the city of Beauvais, where in a few days a moderate temperature record of 24.8°C turned to a record low temperature of -6.9°C! Agricultural losses were sometimes significant, sometimes in all affected wineries. No region could avoid this. This episode with serious consequences for farmers has already followed two black years in terms of frost: 2017 and 2019. Therefore, today, in connection with forecasts for the coming days, Farmers are getting ready for tough days again.

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. For example, in Paris, the maximum temperature will drop from 18°C ​​on Tuesday afternoon to just 11°C on Wednesday afternoon, 3°C below normal. In the south, the weather will continue to be moderate, but a second, more significant drop is expected between Thursday and Friday. We will then be back 5-10°C below seasonal norms 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 pay close attention to the risk snow episode between 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 thinning erupts, frosts may well be severe. As a result, some models provide temperature drops up to -5°С on the plain and up to -10°С close to the Vosges and the Massif Central. Of course, 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?

You may have already noticed that fruit trees have already appeared in most tree regions a few weeks ago, especially after the mild period that we have just experienced in recent days. Therefore, they will be particularly susceptible to frost and cause great damage to gardeners on some farms. As far as viticulture is concerned, Burgundy seems to be the most at risk, because the vine is 7-15 days ahead of schedule due to the exceptional softness of the last few days. In Bordeaux, the vine is fairly late, which is good compared to last year, but all but the late-pruned sites should reach the cotton bud stage when the risk is good. The Departmental Federation of Trade Unions of Agricultural Exploiters of the Gironde (FDSEA 33) also recommends that the wine growers of the department protect themselves from this weekend. One of the other additional worries of winegrowers and gardeners today is also the presence of moisture in the air and on the ground due to rain or snow on Thursday and Friday and showers expected this weekend. Indeed, water that seeps into the buds can cause them to burst much more easily. Finally, possible snow on the ground in some regions, such as Burgundy-Franche-Comté and Center-Val-de-Loire, could increase nighttime radiation and then increase frost and therefore potential damage to crops.

So after a particularly mild start to spring, winter has decided to make a comeback this weekend. In the days leading up to the episode, farmers are already preparing to limit their losses after a string of gloomy years. If the potential for significant cooling this season is currently set, last-minute adjustments will need to be made as the situation is still uncertain regarding certain parameters such as cloud cover and snowfall or the snowfall that preceded it.

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