Comparative study of the soil thermal regime in arid and semi-humid areas

Abstract

The thermodynamic properties of soil affect the energy and water exchange processes between land and the atmosphere and represent an underlying surface property that is a focus of land surface models. In this paper, Dunhuang represents the arid area, and Pingliang represents the semi-humid area. Observation data from 2013 to 2015 from two stations are used to comparatively analyse the differences in soil regime. The results indicate that the amplitude of the soil temperature and soil temperature gradient at Dunhuang is obviously greater than that at Pingliang, and the surface net radiation, soil heat flux, and soil thermal conductivity are obviously smaller than those at Pingliang. At Dunhuang, the annual average soil thermal conductivity at 2.5 and 7.5 cm is 0.21 and 0.24 W m⁻¹ K⁻¹, respectively, whereas at Pingliang, the annual average soil thermal conductivity at 5 and 20 cm is 1.22 and 1.46 W m⁻¹ K⁻¹, respectively. Without considering the freezing of soil, the relationship between the soil thermal conductivity and soil moisture at the two stations passes the significance test at the level of 99%. The soil heat flux is mainly affected by the surface net radiation. The correlation coefficient between the soil temperature gradient at the two stations and the net radiation and soil heat flux passes the 99% significance test. The estimated proportion of the melting latent heat of ice in the soil layer at 5–20 cm at Pingliang in 2014 and 2015 relative to the heat storage of the soil layer at 5–20 cm in March is 20.53 and 24.65%, respectively. The melting heat absorption of ice causes an increasing soil temperature gradient, and increases the heat flux transferred from surface to deeper soil layers.