Abstract
A series of model sensitivity simulations are carried out to calibrate and improve the Weather Research and Forecasting Model coupled with a one-dimensional lake model (WRF-Lake) based on observations over Lake Nam Co. Using the default lake model parameters, the solution of WRF-Lake exhibits significant biases in both the lake thermodynamics and regional climatology, i.e., higher lake surface temperature (LST), earlier onset of summer thermal stratification, and overestimated near-surface air temperature and precipitation induced by the lake’s excessive warming and moistening impacts. The performance of WRF-Lake is improved through adjusting the initial lake temperature profile, the temperature of maximum water density (Tdmax), the surface roughness length, and the light extinction coefficient. Results show that initializing the water temperature with spring observation mitigates the LST overestimation and reduces the timing error of the onset of thermal stratification. By further adjusting Tdmax from 4 °C to the observed value of 3.5 °C, the LST increase from June to mid-July is enhanced and the buildup of thermal stratification is more accurately predicted. Through incorporating the parameterized surface roughness length and decreasing the light extinction coefficient, the model better reproduces the observed daily evolution of LST and vertical lake temperature profile. The calibrated WRF-Lake effectively mitigates the overestimation of over-lake air temperature at 2 m height and precipitation over regions downwind the lake. This suggests that an improved lake scheme within the coupled WRF-Lake is essential for realistically simulating the lake–air interactions and the regional climate over the lake-rich Tibetan Plateau.
Highlights
The Tibetan Plateau, known as the “Asian Water Tower”, harbors more than 1400 lakes with an individual surface area above 1 km2 (Ma et al 2011; Zhang et al 2019a, b)
To improve the WRF-Lake model’s capability in reproducing the lake thermodynamics and the lake climatic effect over central TP (D03), we evaluated and modified the following lake model parameters based on the different properties between plain fresh lakes and Lake Nam Co
During the simulation period (May 20th to August 31st, 2013), the observed epilimnion temperature almost exhibits an identical value from the lake surface to 6 m depth (Wang et al 2019)
Summary
The Tibetan Plateau (hereafter TP), known as the “Asian Water Tower”, harbors more than 1400 lakes with an individual surface area above 1 km (Ma et al 2011; Zhang et al 2019a, b). As the water body is characterized by lower albedo, smaller surface roughness length, larger heat capacity and thermal conductance when compared with the other land types, the exchanges of water and energy at the lake–air interface distinctly differ from those at the land–air interface, causing the spatial heterogeneity of surface thermal conditions over TP (Gerken et al 2013; Ma et al 2014; Song et al 2016) This would further influence the atmospheric circulation, the weather and climate at local and regional scales (Wu et al 2019; Zhu et al 2017). It is imperative to have a comprehensive understanding of the lake–air interactions over TP
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