Regional Mountain Conference

Mountain lakes are often described as sentinels of climate change, a designation earned through their dual high exposure and sensitivity to changing climatic conditions. Although air temperatures in the European Alps have risen at roughly twice the global average, long-term warming rates in mountain lakes often remain muted and diverge from trends observed in lowland or ice-free systems. Increasing evidence suggests that this discrepancy is driven by cryospheric controls, particularly snowpack, late-lying snow, and glacial melt. Snowmelt inflows can delay spring warming, disrupt stratification, and reduce summer heat accumulation by advecting cold water through lakes and shortening water residence times. These processes are captured in a three-phase conceptual framework, that we proposed in a previous study, in which alpine lake heat budgets transition seasonally between ice-dominated, watershed-dominated, and atmosphere-dominated regimes. From a detailed multi-year heat budget study of a mountain lake, we showed that the magnitude of water warming during the open-water season depends on the length of the watershed-dominated phase.

Although mechanistically interesting, the previously applied heat budget approach has limited generalizability, as it requires detailed hydrological measurements that are rarely available for remote alpine lakes.  Here, we aim to test whether the three-phase conceptual model can be used to assess alpine lakes’ vulnerability to warming under climate change in a data-limited context. We analyse the heat budgets of 23 alpine lakes in the Lacs Sentinelles network, in the French Alps. Using differences between modeled vertical heat fluxes and observed changes in lake heat content, we infer the timing and duration of watershed-dominated periods without direct discharge measurements. We then assess how lake and watershed morphology govern the length of the watershed-dominated phase and the sensitivity to snowpack conditions, deriving a vulnerability map for alpine lakes’ vulnerability to warming.