This study evaluates the performance of Community Land Model version 5 (CLM5) in simulating snow cover during winter over the Tibetan Plateau (TP) and presents a revised snow cover fraction (SCF) parameterization scheme implemented in the model. This is a very interesting and innovative investigation. The results show that the revised scheme appears to reduce SCF biases and alleviates the cold bias over the TP. Generally, the topic is interesting, as it addresses uncertainties in land surface model simulations of snow processes in alpine cold regions. The findings may therefore provide useful insights for further development and improvement of land surface models. I recommend a minor revision. My comments and concerning that need be clarified are as follows.

1. This study focuses on TP snow cover during winter rather than other seasons, the reason behind it shouldbeexplained.
2. The revised scheme parameterizing k_accumand revising N_meltare based on the consideration of withered grass stems (WGS) and terrain characteristics. While, the proposed formulation appears largely empirical, the physical mechanisms linking these factors (WGS and terrain) to the spatial distribution of snow cover seem not be sufficiently revealed. The authors should provide a clearer theoretical justification, explain the choice of functional form.
3. Results show a large reduction in SCF bias (up to ~88%) after optimizing the parameterization. But,it is unclear whether these improvements are spatially uniform across the TP. To identify the advantages and limitations of the revised scheme, it’s suggested to add analysis showing regions where the revised scheme performs particularly well and other regions where biases remain significant.
4. The authors are encouraged to provide a detailed analysis of the energy budget, analyze shortwave and longwave radiation fluxes, sensible and latent heat fluxes, potential changes in snow–albedo feedback, which would help clarify the physical consequences of the revised parameterization scheme.
5. This study does not indicate whether the revised scheme was tested in multi-year or long-term simulations. It is necessary to evaluate that the revised scheme remains stable over longer periods. Specifically, whether interannual variability of snow cover over TP is captured.

Dear authors, Please see attached file my detailed comments. Please let me know if there are unclear points. Best wishes, Xu

Comments on “Optimization of snow cover fraction parameterization in the Community Land Model: implementation and preliminary validation over Tibetan Plateau” (egusphere-2025-6490)

General comment:

This study shows a systematic overestimation of wintertime snow cover fraction (SCF) over Tibetan Plateau (TP) by the Community Land Model version 5 (CLM5), and proposes an optimized SCF parameterization scheme through incorporating the effects of non-growing-season vegetation (withered grass stems) and topographic characteristics, and modifying the accumulation parameter (k_accum) and the melt parameter (N_melt). The optimized scheme is evaluated through preliminary simulations over the TP. According to the results presented, the optimized scheme substantially reduces SCF overestimation and improves the simulation of surface albedo and surface temperature. Overall, the manuscript is generally well organized and clearly written. The proposed optimization has the potential to contribute to improvements of snow cover and related surface energy budgets simulations in CLM5. However, several aspects of the methodology and interpretation still require clarification before the manuscript can be considered for publication. I recommend a moderate revision.

Major comments:

1. Physical basis of the optimized parameterization scheme seems unclear. This study proposes modifying k_accum by introducing the influence of non-growing-season vegetation (withered grass stems) and topographic relief. While the idea is plausible, the physical reasoning behind the selected functional form is not sufficiently explained. The authors are encouraged to clarify why these specific factors are expected to control subgrid snow accumulation probability and how the mathematical form of the parameterization was derived.
2. Universality of the optimized scheme and its applicability beyond the TP should be discussed. Currently, the validation is conducted only over the TP. Given that CLM5 is widely used in globe and it’s implied for other models, it is important to discuss the potential applicability of the optimized parameterization in other regions. Whether the parameters are region-specific or globally applicable, possible limitations when applied to different vegetation types also need be discussed.
3. More evaluations of the optimized scheme should be added. The evaluation mainly focuses on SCF, surface albedo, and surface temperature. While these variables are relevant indicators of snow processes, the evaluation could be strengthened by including additional snow-related variables, such as snow depth or snow water equivalent (SWE).

Minor comments:

1. Line 98: “0.05° × 0.05° dataset” should be “0.05° × 0.05° and 500 m spatial resolution dataset”.
2. It’s suggested to use snow water equivalent instead of snow depth in section 2.4, if the data is available.
3. Figure 1: It's suggested to analyze Fig. 1 in section 3.1 for better understanding the original SCF parameterization scheme, which might be the foundation for the proposed optimization
4. Lines 142-143: it's better to add references to support this perspective.
5. In section 3.4: more detailed information of experimental design should be given, such as integration step, output frequency, component set.
6. Please carefully proofread the manuscript for minor grammatical issues, and consider simplifying several long or complex sentences to improve readability.