Prospective des effets du changement climatique sur le lac d’Annecy : Tendances et défis à venir concernant les services rendus

Les lacs sont des habitats pour de nombreuses espèces, ils constituent une ressource précieuse et offrent de nombreux services écosystémiques. Or les lacs doivent actuellement relever le défi du changement climatique. Dans ce contexte, les élus du Syndicat Mixte du Lac d'Annecy (SILA) se sont prononcés favorablement pour le lancement d’une étude de prospective dont l’objectif est de préciser les conséquences environnementales du réchauffement climatique et de ses changements associés sur l’écosystème du lac d’Annecy, et les impacts attendus sur lés principaux usagés du lac.Cette étude recours au modèle lacustre couplé 1D GLM-AED1 ainsi qu’aux différents scénarios climatiques existants, issus des modèles globaux (IPCC – CMIP6) pour anticiper l’évolution d’indicateurs généraux dé la qualité du lac. Les données de suivis limnologiques (réalisés en partenariat avec le CARRTEL depuis 1966) ont permis de calibrer et valider le modèle. Afin de prospecter les évolutions probables du lac au cours des prochaines décennies cette étude propose une analyse des dynamiques temporelles de 101 métriques dérivés de sept variables fondamentales dé l’eau : Température, oxygène, phosphore, chlorophylle-a, nitrates, carbone organique, extinction de la lumière. Ces métriques ont été estimés dans les couches de surface et couches profondes du lac afin de prospecter les évolutions des processus hydrodynamiques et des cycles biogéochimiques en zone pélagique à l’horizon 2100. Les niveaux de confiance de ces simulations sont estimés et discutés. Différents indicateurs écologiques, développés dans le cadre de la Directive Cadre Eau (2000), ont été estimés pour caractériser la qualité biologique du lac. Les 101 métriques ont été classés par catégories afin d’estimer les effets du changement climatique sur quelques services écosystémiques clefs rendus par le lac : 1) approvisionnement en eau potable et 2) en poissons nobles exploités, 3) attraits esthétiques et culturel, 4) régulation des cycles géochimiques et soutien à la séquestration du carbone et 5) soutien au maintien dé l’état écologique général du lac. Cette étude n’aborde pas la question des pollutions telles que les métaux, les hormones, des microplastiques, ni des conditions écotoxicologiques qui nécessiteraient des études spécifiques

Prospective et effets du changement climatique sur le lac de Tignes

Cette étude prospective, financée par la commune de Tignes, a pour objectif de préciser les conséquences environnementales du réchauffement climatique et de ses changements associés sur l’état et le fonctionnement du lac naturel, ainsi que les impacts attendus sur les principaux usages du lac. L’évolution thermique au sein des deux sous-bassins a été modélisée à l’aide du modèle lacustre 1D GLM1 et des différents scénarios climatiques existants, issus des modèles globaux (IPCC – CMIP6). Des données de suivis limnologiques collectées sur un cycle annuel (de Mars 2022 à Avril 2023), ont permis de calibrer et valider le modèle en se référant aux de métriques de performance tels que le RMSE2 (RMSE < 1.41°C). Les flux entrants ont été considérés comme constants sur toute la période d’étude (2000-2100), mais d’autres scénarios de débits des cours d’eau nécessiteraient d’être testés, afin d’estimer l’effet du retrait du Glacier de la Grande Motte sur le fonctionnement du lac.Afin de donner une image des évolutions probables du lac au cours des prochaines décennies, une analyse des dynamiques temporelles de différentes métriques dérivées de la température a été conduite. Ces métriques ont été calculées dans les couches de surface et les couches profondes du lac afin de prospecter les évolutions thermiques de la zone pélagique à l’horizon 2100. Les niveaux de confiance de ces simulations sont estimés et discutés

Past and future climate change effects on thermal regime and oxygen solubility of four peri-alpine lakes

International audienceClimate change modifies the thermal regime and oxygen solubility in lakes globally, resulting in the alteration of lake habitats. The use of 1D lake models has become the standard in lake research to evaluate the effects of climate change. However, the required global scale forcing parameters have several limitations, such as the need of downscaling. Here, we evaluate the possibility to force mechanistic models by following the long-term evolution of shortwave radiation and air temperature while providing realistic seasonal trends for other meteorological parameters. The performance of 1D hydrodynamic lake models was assessed for long-term variations based on 70 years of limnological data collected by the French Observatory of LAkes (OLA). Further the effects of climate change on the thermal regime and oxygen solubility were analyzed in the four-largest French peri-Alpine lakes. Our results show that 1D models forced by air temperature and short-wave radiation accurately predict variations in lake thermal regime, with RMSE of 1.14°C. According to model simulations in the epilimnion and hypolimnion respectively, during the last three decades, water temperatures have increased by 0.46°C/decades (±0.02°C) and 0.33°C/decades (±0.06°C). Accordingly, O2 solubility decreased by -0.104mg/L/decades (±0.005 mg/L) and -0.096mg/L/decades (±0.011 mg/L) due to thermal change. Based on the ssp370 socio-economic pathway of the IPCC, perialpine lakes will face an increase of 3.80°C(±0.20°C) in the future until 2100. These results suggest important degradation in lake thermal and oxygen conditions as well as habitat loss for endemic species

Past and future climate change effects on the thermal regime and oxygen solubility of four peri-alpine lakes

International audienceAbstract. Long-term effects of climate change on lakes globally will include a substantial modification in the thermal regime and the oxygen solubility of lakes, resulting in the alteration of ecosystem processes, habitats, and concentrations of critical substances. Recent efforts have led to the development of long-term model projections of climate change effects on lake thermal regimes and oxygen solubility. However, such projections are hardly ever confronted with observations extending over multiple decades. Furthermore, global-scale forcing parameters in lake models present several limitations, such as the need of significant downscaling. In this study, the effects of climate change on thermal regime and oxygen solubility were analyzed in the four largest French peri-alpine lakes over 1850–2100. We tested several one-dimensional (1D) lake models' robustness for long-term variations based on up to 63 years of limnological data collected by the French Observatory of LAkes (OLA). Here, we evaluate the possibility of forcing mechanistic models by following the long-term evolution of shortwave radiation and air temperature while providing realistic seasonal trends for the other variables for which local-scale downscaling often lacks accuracy. Based on this approach, MyLake, forced by air temperatures and shortwave radiations, predicted accurately the variations in the lake thermal regime over the last 4 to 6 decades, with RMSE < 1.95 ∘C. Over the previous 3 decades, water temperatures have increased by 0.46 ∘C per decade (±0.02 ∘C) in the epilimnion and 0.33 ∘C per decade (±0.06 ∘C) in the hypolimnion. Concomitantly and due to thermal change, O2 solubility has decreased by −0.104 mg L−1 per decade (±0.005 mg L−1) and −0.096 mg L−1 per decade (±0.011 mg L−1) in the epilimnion and hypolimnion, respectively. Based on the shared socio-economic pathway SSP370 of the Intergovernmental Panel on Climate Change (IPCC), peri-alpine lakes could face an increase of 3.80 ∘C (±0.20 ∘C) in the next 70 years, accompanied by a decline of 1.0 mg L−1 (±0.1 mg L−1) of O2 solubility. Together, these results highlight a critical alteration in lake thermal and oxygen conditions in the coming decades, and a need for a better integration of long-term lake observatories data and lake models to anticipate climate effects on lake thermal regimes and habitats

A crisis of lake hypoxia in the Anthropocene: The long-term effects of climate and nutrients

International audienceAbstract Climate change is altering thermal stratification in lakes worldwide. Reduction in winter mixing lead to prolonged oxygen depletion, lasting for years to centuries, potentially becoming permanent. Although there is convincing evidence of lake deoxygenation globally, its duration, timing, and impacts over decadal to centennial timescales remain uncertain. Here, we introduce a novel model-data assimilation approach using 150 years of limnological and paleolimnological data to evaluate the anthropogenic impact and future of deep dissolved oxygen in Lake Geneva. We find that climate change has influenced winter mixing, with divergent effects on bottom oxygen concentrations before and after eutrophication. Over centennial timescales, eutrophication, not climate warming, triggered unprecedented bottom-water hypoxia. However, by 2100, climate change will be the main driver of hypoxia in Lake Geneva and similar lakes, even with reduced phosphorus concentrations. With climate change locking in the effects of phosphorus loading on hypoxia, the significance of reducing loading remains intact

Unraveling Lake Geneva's hypoxia crisis in the Anthropocene

International audienceRecent decades have witnessed widespread deoxygenation of temperate lakes. The intricate interplay between climate change and nutrient loading and its impact on oxygen dynamics still lacks clear understanding. We develop a paleo-data-model coupling approach to investigate long-term variations of dissolved oxygen conditions in Lake Geneva over the period 1850-2100. Our approach provides first estimates of oxygen baseline conditions and quantifies duration of hypoxia since pre-disturbance. Over the 19 th and 20 th centuries, an increase in DO consumption rates (from 0.3 to 2.5 g O 2 m À2 d À1 ) following nutrient over-enrichment caused the onset of hypoxia, and its intensity and duration were governed by the combined influence of climatic forcing and high phosphorus concentration. In the future, hypoxia will be primarily disrupted by reduced frequency of full mixing events

Past and future climate change effects on thermal regime and oxygen solubility of four peri-alpine lakes

International audienceClimate change modifies the thermal regime and oxygen solubility in lakes globally, resulting in the alteration of lake habitats. The use of 1D lake models has become the standard in lake research to evaluate the effects of climate change. However, the required global scale forcing parameters have several limitations, such as the need of downscaling. Here, we evaluate the possibility to force mechanistic models by following the long-term evolution of shortwave radiation and air temperature while providing realistic seasonal trends for other meteorological parameters. The performance of 1D hydrodynamic lake models was assessed for long-term variations based on 70 years of limnological data collected by the French Observatory of LAkes (OLA). Further the effects of climate change on the thermal regime and oxygen solubility were analyzed in the four-largest French peri-Alpine lakes. Our results show that 1D models forced by air temperature and short-wave radiation accurately predict variations in lake thermal regime, with RMSE of 1.14°C. According to model simulations in the epilimnion and hypolimnion respectively, during the last three decades, water temperatures have increased by 0.46°C/decades (±0.02°C) and 0.33°C/decades (±0.06°C). Accordingly, O2 solubility decreased by -0.104mg/L/decades (±0.005 mg/L) and -0.096mg/L/decades (±0.011 mg/L) due to thermal change. Based on the ssp370 socio-economic pathway of the IPCC, perialpine lakes will face an increase of 3.80°C(±0.20°C) in the future until 2100. These results suggest important degradation in lake thermal and oxygen conditions as well as habitat loss for endemic species

Impact passé et futur du climat sur le régime thermique et la solubilité de l'oxygène dans quatre lacs péri-alpins

International audienceClimate change modifies the thermal regime and the oxygen solubility of lakes globally, resulting in the alteration of ecosystem processes, lake habitats and concentrations of key parameters. The use of one-dimensional (1D) lake model for global scale studies has become the standard in lake research to evaluate the effects of climate change. However, such approach requires global scale forcing parameters which have several limitations that are barely discussed, such as the need of serious downscaling. Furthermore, projections of lakes' thermal regime are hardly ever confronted with long-term observations that extent for more than a few decades. These shortfalls limit the robustness of hindcast/ forecast simulations on decadal to centennial timescales. In this study, several 1D lake models' robustness was tested for long-term variations based on 63 years of limnological data collected by the French Observatory of LAkes (OLA). Here we evaluate the possibility to force mechanistic models by following the long-term evolution of shortwave radiation and air temperature while providing realistic seasonal trend for the other parameters for which local scale downscaling often lacks accuracy. Then, the effects of climate change on the thermal regime and oxygen solubility were analyzed in the four-largest French peri-Alpine lakes. Our results show that 1D lake models forced by air temperatures and short-wave radiations accurately predict variations in lake thermal regime over the last four to six decades, with RMSE <1.95 °C. During the last three decades, water temperatures have increased by 0.46 °C decade–1 (±0.02 °C) in the epilimnion and 0.33 °C decade–1 (±0.06 °C) in the hypolimnion. Concomitantly and due to thermal change, O2 solubility has decreased by -0.104 mg L–1 decade–1 (±0.005 mg L–1) and -0.096 mg L–1 decade–1 (±0.011 mg L–1) in the epilimnion and hypolimnion, respectively. Based on the ssp370 socio-economic pathway of the IPCC, perialpine lakes could face an increase of 3.80 °C (±0.20 °C) in the next 70 years, accompanied by a decline of 1.0 mg L–1 (±0.1 mg L–1) of O2 solubility. These results suggest important degradation in lake thermal and oxygen conditions and a loss of habitats for endemic species

Impact passé et futur du climat sur le régime thermique et la solubilité de l'oxygène dans quatre lacs péri-alpins

International audienceClimate change modifies the thermal regime and the oxygen solubility of lakes globally, resulting in the alteration of ecosystem processes, lake habitats and concentrations of key parameters. The use of one-dimensional (1D) lake model for global scale studies has become the standard in lake research to evaluate the effects of climate change. However, such approach requires global scale forcing parameters which have several limitations that are barely discussed, such as the need of serious downscaling. Furthermore, projections of lakes' thermal regime are hardly ever confronted with long-term observations that extent for more than a few decades. These shortfalls limit the robustness of hindcast/ forecast simulations on decadal to centennial timescales. In this study, several 1D lake models' robustness was tested for long-term variations based on 63 years of limnological data collected by the French Observatory of LAkes (OLA). Here we evaluate the possibility to force mechanistic models by following the long-term evolution of shortwave radiation and air temperature while providing realistic seasonal trend for the other parameters for which local scale downscaling often lacks accuracy. Then, the effects of climate change on the thermal regime and oxygen solubility were analyzed in the four-largest French peri-Alpine lakes. Our results show that 1D lake models forced by air temperatures and short-wave radiations accurately predict variations in lake thermal regime over the last four to six decades, with RMSE <1.95 °C. During the last three decades, water temperatures have increased by 0.46 °C decade–1 (±0.02 °C) in the epilimnion and 0.33 °C decade–1 (±0.06 °C) in the hypolimnion. Concomitantly and due to thermal change, O2 solubility has decreased by -0.104 mg L–1 decade–1 (±0.005 mg L–1) and -0.096 mg L–1 decade–1 (±0.011 mg L–1) in the epilimnion and hypolimnion, respectively. Based on the ssp370 socio-economic pathway of the IPCC, perialpine lakes could face an increase of 3.80 °C (±0.20 °C) in the next 70 years, accompanied by a decline of 1.0 mg L–1 (±0.1 mg L–1) of O2 solubility. These results suggest important degradation in lake thermal and oxygen conditions and a loss of habitats for endemic species

A crisis of lake hypoxia in the Anthropocene: The long-term effects of climate and nutrients

International audienceClimate change is altering thermal stratification in lakes worldwide. Reduction in winter mixing lead to prolonged oxygen depletion, lasting for years to centuries, potentially becoming permanent. Although there is convincing evidence of lake deoxygenation globally, its duration, timing, and impacts over decadal to centennial timescales remain uncertain. Here, we introduce a novel model-data assimilation approach using 150 years of limnological and paleolimnological data to evaluate the anthropogenic impact and future of deep dissolved oxygen in Lake Geneva. We find that climate change has influenced winter mixing, with divergent effects on bottom oxygen concentrations before and after eutrophication. Over centennial timescales, eutrophication, not climate warming, triggered unprecedented bottom-water hypoxia. However, by 2100, climate change will be the main driver of hypoxia in Lake Geneva and similar lakes, even with reduced phosphorus concentrations. With climate change locking in the effects of phosphorus loading on hypoxia, the significance of reducing loading remains intact