Future projections of temperature and mixing regime of European temperate lakes

Abstract

Abstract. The physical response of lakes to climate warming is regionally variable and highly dependent on individual lake characteristics, making generalisations about their development difficult. To qualify the role of individual lake characteristics in their response to regionally homogeneous warming, we simulated temperature, ice cover and mixing in four intensively studied German lakes of varying morphology and mixing regime with a one-dimensional lake model. We forced the model with an ensemble of 12 climate projections (RCP4.5) up to 2100. The lakes were projected to warm at 0.10–0.11 °C decade−1, which is 75–90 % of the projected air temperature trend. In simulations, surface temperatures increased strongly in winter and spring, but little or not at all in summer and autumn. Mean bottom temperatures were projected to increase in all lakes, with steeper trends in winter and in shallower lakes. Modelled ice thaw and summer stratification advanced by 1.5–2.2 and 1.4–1.8 d decade−1 respectively, whereas autumn turnover and winter freeze timing was less sensitive. The projected summer mixed layer depth was unaffected by warming but sensitive to changes in water transparency. By mid-century, the frequency of ice and stratification-free winters was projected to increase by about 20 %, making ice cover rare and shifting the two deeper dimictic lakes to a predominantly monomictic regime. The polymictic lake was unlikely to become dimictic by the end of the century. A sensitivity analysis predicted that decreasing transparency would dampen the effect of warming on mean temperature but amplify its effect on stratification. However, this interaction was only predicted to occur in clear lakes, and not in the study lakes at their historical transparency. Not only lake morphology, but also mixing regime determines how heat is stored and ultimately how lakes respond to climate warming. Seasonal differences in climate warming rates are thus important and require more attention.

Lake heatwaves under climate change

“…Specifically, we compare the heatwave metrics from the original daily FLake simulations to those driven by the climate model projections which we temporally disaggregated, following the methods of ref. 65, to a 3-hour timestep. The results demonstrate only minor differences between the model simulations across the case study sites thus suggesting, for this study, that daily data is sufficient and can simulate lake heatwave responses to climate change.…”

Integrating Perspectives to Understand Lake Ice Dynamics in a Changing World

“…However, significant challenges remain in relation to forecasting. The accurate prediction of input variables that drive ice growth and decay processes (e.g., cloud cover; wind speed; and snow compaction, depth, and density) remains limited, leading to errors in ice‐on or ice‐off dates on the order of weeks (Bernhardt et al, 2012; Bueche et al, 2017; MacKay et al, 2017; Magee & Wu, 2017; Shatwell et al, 2019; Su et al, 2019). Further, calibration for individual lakes is time consuming and presents challenges for scaling to multiple lakes across regional or higher spatial scales.…”

Global lake thermal regions shift under climate change

“…Although light attenuation can affect the mixing regime 43 , the effects on seasonally averaged surface temperature is relatively small 44 compared to the differences between thermal regions. The greater impacts on surface temperature, especially in clear, relatively small lakes suggests such lakes could show some deviation in thermal region from neighbouring lakes.…”