L’empreinte du changement climatique sur le Léman

Climate change and Lake Geneva: the evidence is here! - The long-term monitoring of Lake Geneva, which started at the end of the 1950s, highlights climate induced changes on the thermal properties and dynamics of that particular lake. More recent in-situ measurements have allowed drawing direct and indirect relationships between changes observed in the plankton community and meteorological variability. Analyses from long-term observations and findings of research projects both led to the same conclusion that climate change has already impacted Lake Geneva ecosystems and these impacts are likely to continue when considering the predictions based on climate models. Climate warming has notable effects on water temperature, the dynamic of stratification or mixing of the water column and nutrient availability. Such changes in physical and chemical characteristics of Lake Geneva impact the phenology of plankton communities. Consequently, significant changes can be observed in the seasonal dynamics of plankton and the timing of key-species growth. Furthermore, the reproductive cycle of fish is strongly impacted by water temperature. Changes in spawning-time of some species can thus be observed in Lake Geneva. Changes in the phenology of various interacting organisms disrupt the synchronisms between preys and predators, leading to changes in regulatory mechanisms of population and resulting in changes of abundance and composition in lake communities. Finally, the impact of climate change on Lake Geneva is extremely difficult to forecast because climate change occurs simultaneouslywith other changes (micro-pollutants, invasive species…), it impacts rain and hydrology of rivers influencing chemicalsinputs to the Lake. Forecasting the future of Lake Geneva is thus a particularly ambitious objective that would require complex ecological modeling. Les données récoltées depuis la fin des années 1950 dans le cadre du suivi écologique du Léman mettent en évidence l’impact du réchauffement climatique sur la thermie de ce lac. Les campagnes de suivi plus récentes permettent d’établir des liens concrets entre certains changements au sein des communautés pélagiques et les fluctuations météorologiques. De par ces observations et les différentes études menées dans le cadre de projets nationaux et internationaux, il est évident que le réchauffement climatique a déjà posé son empreinte sur le Léman. Le réchauffement du climat influence la température des eaux, les processus de st