In Bordeaux, two appellations have decided to equip themselves with collective anti-hail means using hygroscopic salt technology Selerys. For the climatologist Jean-François Berthoumieu, this solution is the only one capable of increasing the amount of precipitation from storms in the form of rain instead of hail.

” While silver iodide increases snowfall, it does not reduce hail risk or hailstone size, and does not promote rain ‘ says Jean-François Berthoumieu with certainty. The 68-year-old climatologist, director of theClimatological association of the middle Garonne and the south-west (ACMG), now acts as a consultant to various organizations including the Saint-Émilion wine advice who recently chose the Selerys solution to protect themselves from hail.

” I worked on hail control with silver iodide during my postdoc in Canada and previously with air seeding in Lot-et-Garonne. But already in 1984, when I was studying the formation of hailstorms without seeding with the help of a 5 cm radar from Météo France, I understood that everything that had been explained to me about the iodide of money did not work with hailhe clarifies. We have actually observed that only 8% of thunderstorms produce hail from May to Septemberthat form at high altitude and that the likelihood that silver iodide could have any effect was extremely remote. With 92% of storms not producing hail, it remains easy to fool people into believing that seed solutions are effective. Some therefore continue to invest in this technology for psychological rather than scientific reasons. Also, ground-launched seeding with silver iodide has even less chance of getting to the right place than hoping for small hailstones by plane.. »

hygroscopic salts

Based on the work done by the ACMG, members of the Saint-Émilion Wine Council voted in favor in early 2021 Invest in a collective tool to combat hail by choosing Selerys’ Skydetect technology, says Franck Binard, director of the Wine Council. ” The system was adopted at the end of January 2021 and 37 shooting stations were created on 7,500 hectares in the AOCs Lussac Saint-Émilion, Puisseguin Saint-Émilion, Saint-Émilion and Saint-Émilion Grand Cru. » In the event of an alarm, helium-filled biodegradable balloons carrying flares charged with hygroscopic salts are released into thunderstorm cells that may carry hail. A radar placed in the center of the appellation detects storm cells within a 60 km radius. Volunteer winemakers activate the shots.

A voluntary contribution was decided, the amount of which varies depending on the appellation and thus on the evaluation of the wines (40 to 200 euros/ha), to cover the initial investment budget and annual operating costs. “ The experiment is set for 7 years. The technology does not guarantee zero risk, but we hope to reduce the risk of hailstorms on protected areas by 60-70% says Frank Binard. Two years on, the appellation area has not been acclaimed while other neighboring vineyards have been affected, giving a first positive point without validating the technology, the manager acknowledges.Saint-Estephe appellation, which was badly hit by hail on June 20, 2022 (damage between 30 and 80%), voted for a hail protection system at its last general meeting in early 2023. Also there the Selerys solution has been elected. A network off seven launchers scattered throughout the appellation covers 1,180 ha and 61 castles. Dangerous clouds are identified thanks to a platform that includes a hail risk assessment tool. Alerted by SMS, email, or voice messages, winemakers can track real-time movement of storm cells listed at three alert levels. This system is to be used from April 2023.

Principle: rain instead of hail
In 1993, the climatologist Jean-François Berthoumieu addressed interest in hygroscopic salts with calcium chloride, for which work was mainly done in South Africa and today in the United Arab Emirates increase precipitation. The large condensation nuclei accelerate the formation of rain, which settles before it rises and turns into hail. ” We have been able to study and observe with radar in real situations the effect of hygroscopic salts on the development of many storms, some of which produced hail before treatment by aircraft. Quite often we observed an average drop of more than 1000m from the high reflectivity headwaters that was our target. However, We haven’t observed enough cases to statistically and impeccably say that this solution workseven if i believe in it. »

Alternatives: Vineyard adaptations to climatic accidents
Today, to continue his work in favor of producers, Jean-François Berthoumieu is committed to “passive control solutions” with crop adaptations to global warming and supports infrastructures in favor of green water. ” The green water, which arises from evapotranspiration of plants and water bodies, then promotes precipitation cycles. Put hedges around plots of 3-4 ha, water them in the first years and years of drought to encourage their rapid growth, develop a vegetation cover, especially in the vines, or even dig ponds up to 10,000 m³goes towards maximizing the green water that is essential for generating rain and rain definitely less hail. Without forgetting that a grassy vineyard limits the problems of erosion and the hedges can limit the flow of cold air at the level of the vine buds and apple trees. Thus, after 5 years, the increased biomass contributes to evaporation, which attracts more rain and is said to ward off hail by reducing the daily thermal amplitude by a few degrees. ‘, he emphasizes, specifying that during a heat wave, a wet, overgrown ground has a temperature that is 6 to 12°C lower than a bare ground.