Excess warming of a Central European lake driven by solar brightening

Abstract

Recent trends in summer surface temperatures of many lakes exceed the corresponding air temperature trends. This disagrees with expectations from lake surface heat budgets, which predict that lake surface temperatures should increase by 75–90% of the increase in air temperatures. Here we investigate the causes for this excess warming for Lower Lake Zurich, a representative deep and stratified Central European lake, by a combined data analysis and modeling approach. Lake temperatures are simulated using a one‐dimensional vertical model driven by 33 years of homogenized meteorological data. The model is calibrated and validated using an equally long time series of monthly water temperature profiles. The effects of individual forcing parameters are investigated by scenarios where the trends of single variables are retained while those of all other forcing variables are removed. The results show that ∼60% of the observed warming of spring and summer lake surface temperatures were caused by increased air temperature and ∼40% by increased solar radiation. The effects of the trends of all other forcing variables were small. Following projections of climate models, the increasing trends in solar radiation, and consequently the excess warming of lake surface temperatures, are not likely to continue in the future.

Optimizing the parameterization of deep mixing and internal seiches in one-dimensional hydrodynamic models: a case study with Simstrat v1.3

“…For the deep lakes (especially for Lake Geneva), the calibrated values of the α parameter tend to be higher than the ones found by previous studies, which ranged from 0.001 to 0.03 for large basins (Schmid and Köster, 2016;Fink et al, 2014b;Finger et al, 2007). There are several reasons that can explain this deviation.…”

On the predictability of lake surface temperature using air temperature in a changing climate: A case study for Lake Tahoe (U.S.A.)

“…It should also be noted that air2water may be limited when dealing with changes in water transparency (as has been the case for Lake Tahoe during the last 50 yr, Jassby et al ; Tahoe Environmental Research Center 2016), which likely modify the parameter governing the stratification dynamics (i.e., ). In addition, the effect of other factors such as changes in solar brightening or wind forcing during the validation period (compared to the calibration period) cannot be directly captured by the simple structure of the model (except, indirectly, through their potential effect on AT ), despite the fact that they have been shown to be important in some lakes (Schmid and Köster ; Woolway et al ). These considerations undoubtedly challenge the application of the model.…”

Transparency, Geomorphology and Mixing Regime Explain Variability in Trends in Lake Temperature and Stratification across Northeastern North America (1975–2014)

“…Solar brightening [39,48] and decreases in cloud cover [49] lead to increased solar radiation reaching the lake surface. Schmid and Köster [39] found that 60% of LSWT in a central European lake was attributable to increasing air temperature, while the remaining 40% was attributable to increased solar radiation due to air quality improvements. In the future, LSWT warming rates may be more consistent with air temperature rates depending on future stabilization in air quality improvements [4,39].…”

“…Schmid and Köster [39] found that 60% of LSWT in a central European lake was attributable to increasing air temperature, while the remaining 40% was attributable to increased solar radiation due to air quality improvements. In the future, LSWT warming rates may be more consistent with air temperature rates depending on future stabilization in air quality improvements [4,39]. Similarly, milder winters, shortening ice cover and less snow cover on ice occurring in NENA and around the northern latitudes [50,51] will all contribute to lowered lake albedo, earlier stratification and longer duration of energy absorption, resulting in intensified summer warming [11,12,52].…”