Performance Evaluation of ERA5-Land in Simulating Thermodynamics of a Subtropical Shallow Lake Against Long-Term Observations

The Freshwater Lake model (FLake) has recently been integrated into the land surface scheme of ERA5 and subsequently downscaled to ERA5-Land, enabling the investigation of global-scale lake thermodynamics at an enhanced spatial resolution. Although ERA5-Land's capability in simulating lake surface water temperature (Ts) has been recognized, its performance in reproducing other critical lake variables remains inadequately explored. This study comprehensively evaluated ERA5-Land atmospheric forcings and lake products against long-term observations at Lake Taihu, a large, subtropical shallow lake. Results show that ERA5-Land captures the surface microclimates reasonably well at Lake Taihu across diurnal to annual scales. Satisfactory performance is also achieved in simulating monthly and annual latent heat fluxes (λE) with a positive bias of 1.0 W m−2 (or 1% of the annual mean). However, water stratification simulated by ERA5-Land is excessively strong in spring and summer. ERA5-Land systematically overestimates downward shortwave radiation (+16 W m−2) and underestimates downward longwave radiation (−13 W m−2) due to cloud cover underestimation. These intrinsic radiative biases only introduce a marginal error in simulated Ts and λE due to the compensation effect between downward shortwave and longwave components. Our proposed correction algorithm can reduce monthly radiative biases both for an independent period at Lake Taihu and at geographically independent Poyang Lake. Notably, despite lacking lake-specific parameter optimization, the default ERA5-Land configuration still outperforms two other FLake simulations using satellite-calibrated parameters in reproducing the multi-year mean Ts. Furthermore, Flake model in ERA5-Land simulates an identical lake warming trend (0.26 °C decade−1 from 1981 to 2020) and a comparable evaporation changing rate (2.9 W m−2 decade−1 from 1979 to 2013) to other independent simulations with tuned parameters, highlighting its reliability for investigating long-term trends in lake thermodynamics.