Operational modelling of the thermal structure of Swiss Lakes: Achievements, challenges, and new horizons

Accurate simulations of lake thermal structure are essential for understanding the impacts of climate change and predicting ecosystem responses. We provide operational simulations of the thermal dynamics of all major and selected smaller Swiss lakes using the one-dimensional hydrodynamic model Simstrat. These simulations are updated daily with five-day forecasts and made openly accessible via the Alplakes platform, which also offers downloadable input and output files.

Model performance is generally excellent for the larger lakes, with RMSE values around 1.0 °C at the surface and 0.5 °C in the deep water, compared to extensive monitoring data. However, notable challenges persist for: (i) lakes with short residence times strongly influenced by inflow dynamics, (ii) managed reservoirs with operational procedures outside the model’s scope, and (iii) small lakes where local interactions (e.g., groundwater exchange, snowmelt) substantially affect thermal properties.

Comparisons with high-resolution data from new temperature monitoring stations and with 3D simulations available for selected lakes on Alplakes provide multiple opportunities for model evaluation, enhancing process understanding and guiding model improvement. Furthermore, coupling Simstrat with biogeochemical models leverages its robust physical simulations for water quality projections. A beta version of an oxygen model is already running operationally with promising results, paving the way for integrated ecological and geochemical forecasting.