Development of surface temperatures of alpine lakes in Austria under climate change

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, for the development of effective management strategies for high-altitude lakes, it is important to understand their response to climate warming. This study aims at both the reconstruction of LST back to 1998 and the projection of LSTs for 21 alpine lakes (1500-2300 m a.s.l.) in the Niedere Tauern region in Austria until the year 2100. 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 1998-2003, and 2019-2020. We subsequently employed the model with the highest fit to reconstruct LSTs for the whole period 1998 to 2003. Furthermore, we estimate LST 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. Under 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 near future (2020-2049).  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. These alterations in the lakes’ temperature regime probably affect multiple limnological parameters related to ecological quality such as primary productivity and trophic state.