Impacts des changements climatiques sur le vignoble neuchâtelois : étude des indices bioclimatiques déterminants

Our results show that the viticultural climate, as illustrated by bioclimatic indices, has warmed considerably (+400 Growing Degree Days and +2°C over the past 40 years). Trends for the Huglin Index, the average temperature during the vine's vegetative period, and the coolness indices of the nights indicate that adaptation measures will be necessary to maintain a production of quality wines. From the perspective of the average temperature during the vine's vegetative period, the viticultural climate has shifted in 50 years from a cold climate, on the edge of the possibilities for cultivating the earliest ripening grape varieties, to an intermediate climate, too warm for the earliest ripening grape varieties according to this index. Our results with the Huglin Index indicate that during the same period, the viticultural climate shifted from the "too cold" category to the "temperate" category, reinforcing the previous observation. Trends with a coolness index of nights, which considers the advancement of the harvest date, show that Pinot Noir will benefit less and less often from cool nighttime temperatures before harvest. These three indices also show that the climate was too cool for quality wine production 50 years ago, and that the rise in air temperatures is also beneficial from this perspective in the region as it allows to produce quality wines. Future perspectives show that regardless of the scenario, the viticultural climate of the Neuchâtel vineyard will continue to warm until the 2050s. For the mid-century and thus the years 2035 to 2064, the RCP4.5 and RCP8.5 scenarios show no significant difference in the trends of the analyzed bioclimatic indices. The average temperature during the vine's vegetative period is expected to be around 17.5°C (17.9°C by the lake and 17°C in the vineyard heights), compared to 15.5°C for the recent period (1991-2020). The viticultural climate will then be in the "warm" category according to this bioclimatic index. A substantial increase in the Huglin Index relative to the Neuchâtel vineyard is also expected. Our results indicate that for the mid-century (2035-2064), we should expect an average of around 2000 Growing Degree Days (2100 by the lake and 1900 in the vineyard heights), compared to 1650 for the recent period (1991-2020) in the region. For the end of the century (2070-2099), the viticultural climate warms very little compared to the mid-century with RCP4.5. Our results with RCP8.5, however, indicate that the end-of-century climate would be a new type of climate. It would be particularly problematic for vine cultivation, being very hot and including an increase in extreme weather events (droughts, torrential rains, etc.). These results indicate a growing need for adaptation measures, without necessarily condemning the cultivation of traditionally grown grape varieties in the region. They do suggest, however, that the cultivation of more heat-tolerant grape varieties than Pinot Noir could be a long-term adaptation measure, as well as a shift to higher altitudes for the earliest ripening grape varieties. Our results regarding vineyard pests indicate that the climate of the Neuchâtel vineyard will become increasingly suitable in general for invasive exotic insects. Results for the European grapevine moth indicate that this species is expected to produce more generations, 3 generations per year out of 4 by the mid-century according to the two scenarios used. For the end of the century, with RCP8.5, it's almost every other year that we would expect to have 3 generations. As sex pheromone traps seem to work relatively well for this species, this is not very concerning for the Neuchâtel vineyard. Our results for the grape leafhopper are more worrying. This species, a carrier of grapevine yellows, is not yet present in the vineyard. The current climate is moderately conducive to the adaptation of this species. Our results for the future indicate that regardless of the scenario (RCP4.5 and RCP8.5), the climate will be ideal for this species in the Neuchâtel vineyard. The cantonal vineyard station in Auvernier has already developed a surveillance strategy, with the installation of dozens of traps aimed at preventing a surprise and uncontrolled arrival of this species in the region. Our results confirm that this strategy is necessary and appropriate. Other results, which have not been the subject of scientific publications, have also been produced. These include the risk of spring frosts and the frequency of days with problematic thresholds for vine cultivation (30 and 35°C). Our results on spring frosts indicate that the risk of encountering this phenomenon should remain stable in the coming decades, regardless of the climate scenario. This risk should even decrease if later-ripening grape varieties replace some of the early-ripening varieties currently grown in Neuchâtel. Our results concerning temperature thresholds indicate that it will be increasingly common to encounter temperatures above 30°C and 35°C during the summer. While these temperatures were rarely reached before the 1990s, it will be normal to have around twenty days where the temperature exceeds 30°C by the mid-century. For the end of the century, it depends a lot on the scenarios and RCMs used. Most RCMs show a discrepancy between measured and simulated data for the current period, which seems to confirm that the increase in summer temperatures for Central Europe is underestimated in most GCMs (Global Climate models) and RCMs (Regional Climate models). Our various results demonstrate how much climate change can affect agriculture and how important it is to grasp its complexity to anticipate future problems and adapt in advance to ensure the sustainability of agricultural production.