Abstract Unfrozen water plays an important role in a number of processes, including water and heat transfer, frost heave, thaw settlement and simulations for the hydro-thermo-mechanical interactions in frozen soil. Past studies have demonstrated that considering the unfrozen water content in cold regions can significantly improve accuracy in coupling heat and water transfer modeling in frozen soil. However, differences between experimental data and theoretical understanding have resulted in discrepancies between parameterizations. To address this, we presented the first study to synthesize the algorithms and parameterizations used for unfrozen water content; we also discussed influential factors on unfrozen water content in frozen soil. We then provided a comprehensive discussion of the progress in algorithms and parameterizations regarding unfrozen water content and summarized them into four categories, which were calculated using soil temperature, specific surface area of soil particles, soil water curve, and different types of water. Selected unfrozen water content parameterizations were then evaluated based on those previous results as well as the data collected from our field observation station in permafrost region on the Qinghai-Tibet Plateau (QTP). These results revealed that empirical parameterizations were useful for calculating unfrozen water content. In addition, the physical parameterizations had higher accuracy for calculating unfrozen water content, but they were more complicated and difficult to use in practical applications. Unfrozen water content parameterizations were influenced by many factors, and the warming and cooling processes were especially important when calculating unfrozen water content. Finally, future research should aim to improve our theoretical understanding and to develop simple parameterizations that couple land surface processes models in cold regions. It is expected that this review will provide a sound theoretical basis for the further study of the unfrozen water content in frozen soil and its subsequent effects on hydrothermal transfer processes in cold regions.

中文翻译：

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确定冻土中未冻水含量的算法和参数化审查

摘要 未冻水在水热传递、冻胀、解冻沉降和冻土水-热-机械相互作用模拟等许多过程中起着重要作用。以往的研究表明，考虑寒冷地区的未冻水含量可以显着提高冻土传热传水耦合建模的准确性。然而，实验数据和理论理解之间的差异导致了参数化之间的差异。为了解决这个问题，我们提出了第一项研究来综合用于未冻结水含量的算法和参数化；我们还讨论了影响冻土中未冻水含量的因素。然后，我们全面讨论了关于未冻结含水量的算法和参数化的进展，并将它们归纳为四类，分别使用土壤温度、土壤颗粒比表面积、土壤水分曲线和不同类型的水进行计算。然后，根据先前的结果以及我们在青藏高原 (QTP) 多年冻土区实地观测站收集的数据，对选定的未冻水含量参数化进行了评估。这些结果表明，经验参数化对于计算未冻结水含量是有用的。此外，物理参数化在计算未冻水含量方面具有更高的精度，但它们在实际应用中更加复杂且难以使用。未冻水含量参数化受多种因素影响，在计算未冻水含量时，升温和降温过程尤为重要。最后，未来的研究应该旨在提高我们的理论理解，并开发简单的参数化来耦合寒冷地区的地表过程模型。预计该综述将为进一步研究冻土中未冻水含量及其对寒冷地区热液传递过程的影响提供良好的理论基础。未来的研究应该旨在提高我们的理论理解并开发简单的参数化，以耦合寒冷地区的地表过程模型。预计该综述将为进一步研究冻土中未冻水含量及其对寒冷地区热液传递过程的影响提供良好的理论基础。未来的研究应该旨在提高我们的理论理解并开发简单的参数化，以耦合寒冷地区的地表过程模型。预计该综述将为进一步研究冻土中未冻水含量及其对寒冷地区热液传递过程的影响提供良好的理论基础。