Hindcast/forecast of thermal regime and oxygen solubility in four perialpine lakes using 1D model and OLA observatory data | Évolution du régime thermique et de la solubilité de l'oxygène dans quatre lacs péri-alpins à l'aide d'un modèle 1D et des données de l'observatoire OLA

International audience

English. Climate change modifies globally the thermal regime and solubility of oxygen in lakes, resulting in the alteration of lake habitats. The use of 1D lake models has become the standard in lake researches to evaluate the effects of climate change. However, the required global scale forcing parameters have several limitations, such as the need of downscaling. In this study, several 1D lake models' robustness were tested for long-term variations based on 50±13 years of limnological data collected by the French Observatory of LAkes (OLA). We evaluate the possibility to force mechanistic models by following the long-term evolution of shortwave radiations and air temperatures 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 shortwave 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.