Improving a Multilevel Turbulence Closure Model for a Shallow Lake in Comparison With Other 1-D Models

Lakes differ from lands in water availability, heat capacity, albedo, and roughness, which affect local surface-atmospheric interactions. This study modified a multilevel upper ocean model (UOM) for lake applications and evaluated its performance in Lake Taihu (China) with comprehensive measurements against three popular one-dimensional (1-D) lake models. These models were based on different concepts, including the self-similarity (FLake), the wind-driven eddy diffusion (LISSS), thek-epsilon turbulence closure (SIMSTRAT), and a simplified turbulence closure (UOM). The surface flux scheme in these models was unified to exclude the discrepancies in representing air-lake exchanges. All models in their default formulations presented obvious cold water temperature biases and largely underestimated the lake surface temperature (LST) diurnal range. For each model, these deficiencies were significantly reduced by incorporating new physics schemes or calibrated tunable parameters based on systematic sensitivity tests. The primary modifications for UOM included (1) a new scheme of decreased surface roughness lengths to better characterize the shallow lake, (2) a solar radiation penetration scheme with increased light extinction coefficient and surface absorption fraction to account for the high water turbidity, and (3) turbulent Prandtl number increased by a factor of 20 to reduce the turbulent vertical mixing. All other models were improved in these three aspects (roughness, extinction, and mixing) within their original formulations. Given these improvements, UOM showed superior performance to other models in capturing LST diurnal cycle and daily to seasonal variations, as well as summer-autumn vertical stratification changes. The new UOM is well suited for application in shallow lakes. Plain Language Summary Lakes, with unique characteristic differences from lands, play an important role on local-regional weather and climate. This study improved a multilevel upper ocean model (UOM) for a shallow lake application with primary modifications on surface roughness, radiation extinction, and vertical mixing. The model was intercompared against comprehensive measurements with three other improved one-dimensional models based on different concepts in the context of using a unified surface flux scheme to exclude the discrepancies in representing lake-air exchanges. All models in their default formulations presented obvious cold water temperature biases and largely underestimated the lake surface temperature diurnal range. Their performances were significantly improved with the proposed modifications. In particular, the improved UOM showed superior performance to other models in capturing lake surface temperature diurnal cycle and daily to seasonal variations, as well as summer-autumn vertical stratification changes. The new UOM is useful for inclusion in weather and climate models to represent shallow lake processes.