Katharina Enigl, Rainer Kurmayer

Lake Surface Temperature (LST) is a key characteristic that reflects meteorological and climatological influences on lakes. In general, there is limited LST data from high elevation lakes available as these areas are remote and not part of regular monitoring programs. Nonetheless, it is crucial to understand their response to climate warming for the development of effective management strategies for high-altitude lakes. This study aims at projecting LSTs for 21 alpine lakes (1500-2300 m a.s.l.) in the Niedere Tauern region in Austria until the end of the century. For the determination of the relationship between atmospheric variables (temperature and precipitation), near-lake snow depth and observed LST, General Additive Models were trained with a daily temporal resolution for the years 1998 to 2003, 2009 to 2011 and 2019 to 2021. We subsequently employed the model with the highest fit to project LSTs until 2100 using an ensemble of regional climate projections for the RCP2.6 (in-line with the COP 21 Paris Agreement), RCP4.5 and RCP8.5 (“worst-case”) scenario. Considering the RCP8.5 scenario, the average rise for August lake surface temperatures in the far future (2071-2100) is predicted to increase by 2.3 °C compared to temperatures in the reference period (2021-2030). Consequently, the ice-free period is expected to rise on average 1-1.2—fold in the near future (2031-2060) and 1-1.5-fold in the distant future. Furthermore, we evaluated changes in the maximum temperatures of investigated lakes, indicating that 15 °C to 17 °C will be relatively common in the far future period. These alterations in the lakes’ temperature regime probably affect multiple limnological parameters related to ecological quality such as primary productivity and trophic state.