Improvements of the coupled WRF-Lake model over Lake Nam Co, Central Tibetan Plateau

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.

Numerical Study of the Thermal Structure and Circulation in a Large and Deep Dimictic Lake Over Tibetan Plateau

“…The 1‐D model considered the snow, lake water/ice, and soil sediment processes within a lake column (e.g., Gu et al., 2015). WRF‐Lake has undergone significant calibrations and has been applied in simulating the thermodynamics in LNC in offline or coupled settings (A. N. Huang et al., 2019; Wu et al., 2020). In this study, WRF‐Lake is run in un‐coupled mode for the same 8‐month duration using the same initial condition and surface forcing as POM.…”

Convection‐permitting modeling with regional climate models: Latest developments and next steps

“…Moreover, CPRCMs are mainly atmospheric-only models. Large benefits could be achieved by adding Earth system components (Giorgi & Gao, 2018) to CPRCMs such as lake models (Wu et al, 2020), aerosol schemes (Chen, 2021), oceanic models providing improved sea surface temperature gradients (Van Pham et al, 2016), and more sophisticated surface schemes including irrigation (Qian et al, 2020) and groundwater interactions (Barlage et al, 2021).…”

“…Indeed, conducting monthly CPRCM simulations including or not the Lake Nam Co over the Tibetan Plateau, Dai et al (2018) found that the presence of the lake can increase precipitation up to 60% over and downwind the lake. However, CPRCM simulated lake effects are closely linked to the ability of the lake model to represent lake temperatures, dynamics, and initial conditions (Wu et al, 2020; Xu et al, 2017).…”

SIMO v1.0: Simplified model of the vertical temperature profile in a small warm monomictic lake

“…where Sn(z) and Sn(0) are the shortwave radiations at water depth z and at the water surface, respectively, and λe is the light extinction coefficient calculated as suggested by Wu et al (2020):…”