Abstract
Abstract. Lakes are sensitive indicators of climate change. There are thousands of lakes on the Tibetan Plateau (TP), and more than 1200 of them have an area larger than 1 km2; they respond quickly to climate change, but few observation data of lakes are available. Therefore, the thermal condition of the plateau lakes under the background of climate warming remains poorly understood. In this study, the China regional surface meteorological feature dataset developed by the Institute of Tibetan Plateau Research, Chinese Academy of Sciences (ITPCAS), MODIS lake surface temperature (LST) data and buoy observation data were used to evaluate the performance of lake model FLake, extended by simple parameterizations of the salinity effect, for brackish lake and to reveal the response of thermal conditions, radiation and heat balance of Qinghai Lake to the recent climate change. The results demonstrated that the FLake has good ability in capturing the seasonal variations in the lake surface temperature and the internal thermal structure of Qinghai Lake. The simulated lake surface temperature showed an increasing trend from 1979 to 2012, positively correlated with the air temperature and the downward longwave radiation while negatively correlated with the wind speed and downward shortwave radiation. The simulated internal thermodynamic structure revealed that Qinghai Lake is a dimictic lake with two overturn periods occurring in late spring and late autumn. The surface and mean water temperatures of the lake significantly increased from 1979 to 2012, while the bottom temperatures showed no significant trend, even decreasing slightly from 1989 to 2012. The warming was the strongest in winter for both the lake surface and air temperature. With the warming of the climate, the later ice-on and earlier ice-off trend was simulated in the lake, significantly influencing the interannual and seasonal variability in radiation and heat flux. The annual average net shortwave radiation and latent heat flux (LH) both increase obviously while the net longwave radiation and sensible heat flux (SH) decrease slightly. Earlier ice-off leads to more energy absorption mainly in the form of shortwave radiation during the thawing period, and later ice-on leads to more energy release in the form of longwave radiation, SH and LH during the ice formation period. Meanwhile, the lake–air temperature difference increased in both periods due to shortening ice duration.
Highlights
The Tibetan Plateau (TP) is the highest plateau in the world, known as the Earth’s “third pole” (Qiu, 2008), and exerts a significant influence on regional and global atmospheric circulation through its dynamic and thermodynamic effectsPublished by Copernicus Publications on behalf of the European Geosciences Union.D
The reason is the difference in the physical characteristics, in particular, air temperatures and wind speeds, between land and water, which is especially strong over the TP (Lazhu et al, 2016)
They found that the model overestimated the lake surface temperature (LST) when compared with the MODIS data because the forcing data were obtained at the land station rather than over the lake surface
Summary
The Tibetan Plateau (TP) is the highest plateau in the world, known as the Earth’s “third pole” (Qiu, 2008), and exerts a significant influence on regional and global atmospheric circulation through its dynamic and thermodynamic effects. The surface water warming rates of lakes are mainly driven by the increasing air temperature (Adrian et al, 2009; Schmid et al, 2014), depending on combinations of climate and local characteristics that are associated with interactions among different climatic factors. Lakes are predicted to experience a cooling trend despite a significant increase in the air temperature over the plateau (Kirillin et al, 2017) that demonstrates decoupling of the air and land response to the global change and suggests a nonlinear response of the entire hydrological system. In addition to quantifying the recent climate change effects on the thermal regime of China’s largest lake, the second aim of the study is to test the FLake performance on brackish lakes after parameterizations of the salinity effect on the temperature of maximum density and freezing point in the model. We applied the freshwater lake model to a brackish TP lake in order to (i) evaluate the ability of the lake model FLake to simulate the main thermodynamic features of the lake in high-altitude conditions and (ii) validate the performance of a freshwater lake model, extended by simple parameterizations of salinity effects, for a brackish lake
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