Surface thermal patterns of Lake Geneva, Switzerland, from 2008 to 2012

In this study we characterize the spatial and temporal variability of the lake surface water temperature (LSWT), lake surface heat fluxes as well as the heat content of Lake Geneva from March 2008 to December 2012. This was accomplished using Advanced Very High Resolution Radiometer (AVHRR) data for the LSWT and an operational numerical weather prediction model, namely COSMO-2, for the meteorological data. Available bulk models for different components of the surface heat flux were cataloged and then combined (using all possible combinations). Each of the assembled models was calibrated to produce the best overall model for the surface heat flux. Calibration was based on the temporal evolution of the heat budget, which was estimated using two long-term time series of vertical temperature profiles (one in the Lake Geneva’s large basin and one in its small basin). Empirical Orthogonal Function (EOF) analysis was used to assess the relationship between the variability of the LSWT and meteorological forcing. The dominant EOF mode, which explains 74% of the observed variance for wind speed, 78% for evaporative heat flux and more than 90% for other parameters, shows uniform patterns associated with the annual cycle. Their temporal amplitude reveal a time lag between total surface heat flux and LSWT variation. On the other hand, some zones are detectable in the spatial patterns of the second and third modes. This analysis indicates a good correlation between the variation of wind forcing and evaporative heat flux in the first three modes.