Disproportionate impact of atmospheric heat events on lake surface water temperature increases

Hot temperature extremes (HTEs) in the atmosphere can also affect lake surface water temperature, but how this impact changes with global warming is not well understood. Here we use numerical modelling and satellite observations to quantify the contribution of HTEs to variations in summer lake surface water temperature and lake heatwaves in 1,260 water bodies worldwide between 1979 and 2022. Over this time period, HTE duration and cumulative intensity over the studied lakes increased significantly, at average rates of 1.4 days per decade and 0.92 °C days per decade, respectively. Despite only accounting for 7% of the total summer days, HTEs are responsible for 24% of lake surface summer warming trends, with the most pronounced effect observed in Europe at 27%. Moreover, HTEs are key drivers of both the duration and cumulative intensity of lake heatwaves. Our findings underscore the pivotal role played by short-term climatic extreme events in shaping long-term lake surface water temperature dynamics. Lake surface water temperatures have increased over recent decades, mainly driven by atmospheric conditions. Here the authors demonstrate that heat events drive a disproportionately large part of this lake surface warming and increases in lake heatwaves.