After a particularly mild winter, France saw its temperatures drop and its skies darken at the start of spring. This Friday, April 1, 2022, Météo-France has also placed 22 departments in orange vigilance “snow and ice”. The thermometer panics and sees some regions lose up to 25°C overnight. Fearing a similar scenario in the spring of 2021, French farmers reacted by installing anti-frost nets and other candles to prevent the frost damage expected this first weekend of April 2022.
Scandinavian cold air
The wave of cold and humid air crossing France has broken away from the polar vortices. These form large depressions at high altitudes, rotating around the poles at the level of northern Norway. “This cold air mass migrated towards France and was accelerated by a humidity-laden depression resulting in rainy and snowy precipitation on the first two days of the episode. It is after the passage of rainfall and the drop in the wind that the frost will begin to set in and cause damage to crops. mainly on the eastern half of the territory” explains to Science and Future l’agroclimatologue Serge Zaka from ITK company.
In 2021, the frost caused heavy damage linked to an early flowering of the buds, due to a winter that was milder than normal for the season. “It is not the cold snap that is exceptional, but the winter which was abnormally mild, again this year. The phenomenon of alternating between cold and hot waves is typical of early spring. Here, the difference with 2021 is that certain varieties of plants, still in bud, will not be affected by frost, while those with a phenological stage (periodic events such as flowering, leafing or fruiting, linked to the seasons, editor’s note) advanced will suffer heavy losses” explains Serge Zaka. Local frost forecasts are all the more difficult to estimate for our models because of the complexity and speed of the very wet low.”
The white gel and the black gel
Freezing refers to a simple drop in temperature equal to or less than 0°C. If it looks like a simple layer of white ice, it is nonetheless devastating in some cases and can even burn the buds. “There are two types of frost: white, which forms with humid air and light wind, visible by the layer of frost it forms on the surfaces, and black, invisible, which occurs with dry air and stronger winds, describes the agroclimatologist. There is no difference in impact between the two, however, when powdery mildew is easily avoidable with means of control such as anti-freeze nets or candles, black is more difficult to counter due to strong winds that accompany it and take the heat of the protections with it.”
“The percentage of tree production loss is still difficult to estimate”
Like last year, French farmers are expecting losses, especially in the tree sector. “The percentage of tree production loss is still difficult to estimate. We already know that varieties such as apricots, cherries or Mirabelle plums are already at an advanced phenological stage and will be particularly affected, compared to vines, apples and pears. which have not yet broken in. The forecasts will be much more accurate when the clouds have cleared and the winds will therefore be easier to model, says the agroclimatologist. However, a chance remains for the plots located around the Rhône valley and around the Mediterranean basin with the maintenance of a strong wind, preventing frost from settling there. Or, more paradoxically, the covering of a blanket of snow on the trees which would protect the buds from freezing, but this is less likely. »
When most farmers do not hesitate to help their neighbor to install anti-freeze devices, agroclimatologists make sure to provide precise information adapted to each one to guarantee maximum protection against the vagaries of nature. “To probe the varieties that will be affected and estimate the associated losses, we use various meteorological models such as the ECMWF (European Centre for Medium-Range Weather Forecasts) European or the American GFS (Global Forecast System) on which we superimpose data from the participatory phenological census such as that of the Observatory of the seasons developed by CNRS and INRAE. I also carry out a census with the farmers themselves through social networks. This collaboration allows me to collect as much information as possible to draw up the most precise maps possible to give all the information necessary for farmers to be better prepared. Good cooperation is essential in this environment to understand this kind of event”.
[MAJ, 31/03] The modeling of tree production losses still considers a major risk on the 🇫🇷.
Changes since yesterday:
– ↗️ damage in the west, Mediterranean hinterland & Alsace.
– ↘️ damage in the Paris basin (cloud layer).#gel #snow #FrAgTw pic.twitter.com/dshQ8NElH9– Dr. Serge Zaka (Dr. Zarge) (@SergeZaka) March 31, 2022
Limited solutions
The future of arboriculture is threatened by the intensification of climate change:“the chances of re-experiencing this type of event will increase” according to the agroclimatologist. “Replacement by more cold-resistant varieties or with later flowering is possible for cereal crops but much more complicated for arboriculture. The replacement of fruit trees is a much more complex process and requires several years before becoming profitable for the operator. Some are also subject to quality constraints and AOP (Protected Designation of Origin) standards, particularly in the wine-growing area”concludes Serge Zaka.
You can contribute to the census of plants and their phenological stage by participating in the “Observatory of the seasons” program throughout the year by observing the nature that surrounds you by clicking here.
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