News Weather
The winter was abnormally mild (+2°C), with heat peaks from the end of January-beginning of February in the south. The threat of damage linked to spring frost now hangs like a sword of Damocles over the heads of farmers due to very early vegetation this year.
The Weather Channel: What assessment do you draw from this mild winter and what are the impacts of this mildness on the vegetation?
Cyril Wuest : We must already put things in context. This meteorological winter 2023-2024 was particularly mild, reaching an overall thermal anomaly of +2°C. It was especially the month of February which was exceptional with an anomaly which reached +3.5°C, which places it in 2nd position of the mildest since 1900 in France.
Even more surprising, on the whole of this month bissextileL’national thermal indicator only went one day below normal. Finally, some cities, although accustomed to frost, had to wait until the last day of the month to see their thermometer drop below 0°C, like Strasbourg or Besançon. Other cities did not experience a single day of frost, such as Lyon or Bourges which had 42 consecutive days without frost.
With such mild spring weather, the phenology of plants (the vegetative stages) is far too advanced this year (by one month on average), which increases their sensitivity and vulnerability to frost hazards. Since the end of February, apricot and plum trees in the south have already bloomed, while their flowering period is supposed to begin at the end of March. Budburst (or budburst), in other words the opening of the buds, occurs early in almost all species. For apples and pears, the flowering period is later, therefore with a lower risk for these crops.
LCM: Why does the early advance of vegetation pose a greater risk for different crops, whether for fruit trees or vines?
C.W. : Although the winter was mild, the risk of frost still exists until the end of April, and even until May for regions close to the northeastern borders. With the precocity of flowering and bud burst, the period of conjunction between the risk of frost and flowering creates a longer period of vulnerability than in a normal year where flowering begins later.
As a crop’s phenological stage advances, its tolerance for cold temperatures decreases. For example, the apple tree can withstand temperatures of -7°C at the start of bud swelling, while it will not be able to withstand temperatures below -2°C after flowering, because its fragility increases. We are typically in a situation where if a hard frost occurs, crops will not survive.
This situation occurred recently in April 2021 and 2022, where a period of late frost occurred on crops whose vegetative stages were well advanced, causing damage and colossal yield losses (estimated at 2 billion euros) . The same situation happened again last year, also at the beginning of April, but to a lesser extent.
LCM: You are monitoring a risk of frost for the start of next week. What should you expect?
C.W. : Indeed, after the spring atmosphere of this week, with a sometimes summer feeling in the south, the situation is going suddenly change this weekend, with a drop of 10°C on average. This return to winter will initially be humid and windy, which will limit the risk of surface frost. But, for the start of next week, a risk of frost is not excluded if the sky clears during the night, and the weather becomes drier. The analysis of the coming days will allow us to respond more reliably to what awaits us. Beyond this deadline, and as mentioned previously, freezing may occur until May. Even if these situations are increasingly rare with global warming, it is a risk to monitor.
LCM: Is climate change increasing the risk of spring frost?
C.W. : Climate change has the effect of contracting the winter season (winter lasts less long) and reducing the intensity of winters which are therefore less cold and shorter. Thus, despite the warming trend, the risk of frost damage increases significantly due to the advance of vegetation caused by these increasingly mild conditions.
