Optimization and Validation of Soil Frozen‐Thawing Parameterizations in Noah‐MP

AbstractWater‐heat transport in frozen soil influences the energy and water exchanges between land and atmosphere. However, frozen soil water‐heat transport simulation biases remaining in land surface model (LSM) result in uncertainties of climate model performance. In this study, the biases of the Noah with multi‐parameterization (Noah‐MP) land surface model in simulating soil water‐heat transport in freeze‐thaw (FT) process were investigated. On this basis, three parameterizations that were effective in other LSMs were implemented into Noah‐MP to optimize its performance. The results show that Noah‐MP still exhibits biases in simulating soil temperature and moisture in FT process. Even with various combinations of current parametrizations, the soil water–heat coupling relationship simulated by Noah‐MP does not align with observations. Nevertheless, the implementation of a virtual temperature parameterization, a liquid water‐dependent soil permeability parameterization, and modifications to soil hydraulic and thermal properties through considering the influences of organic matter and gravel, led to improvements in soil moisture and temperature simulations during both completely frozen and thawing periods. These enhancements resulted in a reduction of bias by approximately 20%–50%, and the simulated soil water–heat coupling relationship with implemented parameterizations closely matches observations. Global simulations further validate the improvements brought about by the implemented frozen‐thawing parameterizations in Noah‐MP.