The science in this inter-disciplinary project included a retrospective analysis of past extreme events in lakes (such as the 2018 European heatwave) to understand commonalities and differences across lake types (e.g. lake location and depth), and provide insight into the consequences of the increased occurrence of climatic extremes in the future. Using high frequency data from monitoring buoys to calibrate an ensemble of lake models, the project contributed to the generation of global lake projections within the ISIMIP Lake Sector. These simulations were then used by the researcher to investigate the intensity and duration of lake stratification under climate change and the increased occurrence of extreme events. This study is the first to use an ensemble of lake and climate model projections to simulate lake thermal responses to climate change, and the manuscript is currently under review.
To investigate the thermal response of 46,557 lakes to the 2018 European heatwave, a lake model, validated with satellite derived observations from 155 lakes from 1995 to 2018, demonstrated that the 2018 heatwave had a considerable influence on lake surface temperatures across the continent. Overall, the increase in air temperature had the strongest influence. However, in some lake regions, other meteorological forcing had a greater influence. Notably, higher than average solar radiation and lower than average wind speed exacerbated the influence of the heatwave on lake surface temperature in many regions, particularly Fennoscandia and Western Europe. To place the results in the context of projected 21st century climate change, the lake model was then run with input data from state-of-the-art climate model projections under three climate change emissions scenarios. Under the scenario with highest emissions (Representative Concentration Pathway 8.5) it was demonstrated that by the end of the 21st century, the lake surface temperatures that were recorded during the heatwave of 2018 will become increasingly common across many lake regions in Europe.
A one-dimensional lake model was also used to simulate the response of lakes to the increased occurrence of extreme events under climate change. Specifically, the researcher developed a new metric for identifying extreme events in lakes, termed lake heatwaves. In this work, an ensemble of climate model projections was used, under different climate trajectories, to force a lake model from 1901 to 2099. Lake heatwaves were defined as a period in which daily lake surface temperatures exceed a local and seasonally varying 90th percentile threshold, relative to a baseline climatology, for at least five days. The project investigated how lake heatwave intensity and duration responded to climate change and simulated lake heatwave events from 1901 to 2099. Metrics were derived for duration and intensity of lake heatwaves. In addition, an intensity-based lake heatwave category was used to define the relative strength of each lake heatwave, where each event was classed as being Moderate, Strong, Severe, or Extreme. The work demonstrated that lake heatwaves will become more intense and longer lasting by the end of the 21st century.
