Preprints
https://doi.org/10.5194/hess-2023-44
https://doi.org/10.5194/hess-2023-44
06 Mar 2023
 | 06 Mar 2023
Status: this preprint is currently under review for the journal HESS.

A calculation method of unsaturated soil water content based on thermodynamic equilibrium

Danhui Su, Jianwei Zhou, Zuocong Yin, Haibo Feng, Xiaoming Zheng, Xu Han, and Qingqiu Hou

Abstract. Accurate determination of soil water content is crucial for studying the local ecological water cycle, agriculture, forests and grasslands management, slope stability, environmental processes, and ecological problems. Current measurement methods of soil water content have challenges with the complicated operation, high costs, significant system errors, and soil type-specific accuracy. In this study, we proposed an alternative method to measure soil water content using the ratios of mass and density of water to vapor based on system science and thermodynamics. We derived the mass ratio and density ratio of water to vapor as a function of temperature from published data and validated the accuracy of the proposed method using observed temperature, relative humidity, and volumetric water content in two soil textures of medium and fine sand. We further demonstrated that the mass ratio function is independent of the nature of the water-containing media using theoretical and statistical analysis. The absolute error of soil water content between the calculated and measured ones is less than 1 % and is positively correlated with temperature. This study significantly improves the measurement accuracy of soil water content, eliminates the effect of water-containing medium on soil water content measuring, and has excellent potential for application in the field soil and even rock water content measurement.

Danhui Su et al.

Status: open (until 01 May 2023)

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Danhui Su et al.

Danhui Su et al.

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Short summary
Based on the quantitative relationship between vapor and water in soil, we propose a determination and calculation method for soil water content. This method significantly improves the measurement accuracy of soil water content, eliminates the effect of the soil properties on soil water content measuring, and has excellent potential for application in the field soil and even rock water content measurement.