Diurnal pattern of liquid water and water vapor movement affected by rainfall in a desert soil with a high water table

Abstract

Because arid and semi-arid regions have relatively low soil moisture, water vapor movement often occurs predominantly in the unsaturated zone, affecting the partitioning of energy among various land surface fluxes. To understand the hydrological processes of the unsaturated zone in desert areas, it is important to characterize the diurnal and spatial variations in soil water and vapor movement, which control recharge and discharge via the unsaturated zone. However, few studies have examined the pattern of soil water and vapor movement affected by rainfall in desert areas. To understand this process, field observations of desert soil physical parameters and micrometeorological variables were taken. These data were used to verify and calibrate the performance of an unsaturated–saturated zone soil water balance model, Hydrus-1D. Next, the diurnal pattern of the soil water and vapor was simulated under different climatic conditions, i.e., before, during and after rainfall. Two stages of thermal liquid and vapor movement were identified before rainfall. The thermal liquid flux fluctuates quickly and drastically, while the thermal vapor changes more moderately during and after rainfall. The changes in isothermal liquid and vapor flux differ from those of thermal liquid and vapor flux because of the change in the pressure head gradient under various wetness conditions. These findings offer insight into how water vapor affects soil water movement in the semiarid desert. They also improve our understanding of the liquid water and water vapor movement processes following rainfall.