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In 2018, Europe experienced the warmest May–October (Northern Hemisphere warm season) since air temperature records began. In this study, we ran model simulations for 46 557 lakes across Europe to investigate the influence of this heatwave on surface water temperature. We validated the model with satellite-derived lake surface temperatures for 115 lakes from 1995 to 2018. Using the validated model, we demonstrated that, during May–October 2018, mean and maximum lake surface temperatures were 1.5 and 2.4 °C warmer than the base-period average (1981–2010). A lake model experiment demonstrated that, on average, the increase in air temperature was the dominant driver of surface water temperature change. 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 our results in the context of projected 21st century climate change, we then ran the lake model with input data from state-of-the-art climate model projections under 3 emissions scenarios. Under the scenario with highest emissions (Representative Concentration Pathway 8.5), we demonstrated that by the end of the 21st century, the lake surface temperatures that occurred during the heatwave of 2018 will become increasingly common across many lake regions in Europe.

In 2018, Europe experienced the warmest May–October (Northern Hemisphere warm season) since air temperature records began. In this study, we ran model simulations for 46 557 lakes across Europe to investigate the influence of this heatwave on surface water temperature. We validated the model with satellite-derived lake surface temperatures for 115 lakes from 1995 to 2018. Using the validated model, we demonstrated that, during May–October 2018, mean and maximum lake surface temperatures were 1.5 and 2.4 °C warmer than the base-period average (1981–2010). A lake model experiment demonstrated that, on average, the increase in air temperature was the dominant driver of surface water temperature change. 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 our results in the context of projected 21st century climate change, we then ran the lake model with input data from state-of-the-art climate model projections under 3 emissions scenarios. Under the scenario with highest emissions (Representative Concentration Pathway 8.5), we demonstrated that by the end of the 21st century, the lake surface temperatures that occurred during the heatwave of 2018 will become increasingly common across many lake regions in Europe.