Background and aims'Earth-air' refers to air in the vadose zone (VZ). Barometric pumping results in the rising and falling of earth-air in the VZ. Earth-air vertical movement (EVM) has an important effect on water transport in the VZ. However, phreatic water is an important source of water in the Loess Plateau, the effect of earth-air on water content is unclear.MethodsThis paper aims to reveal the effect of earth-air on the water content in the VZ of loessal soil by calculating the amount of earth-air and measuring volumetric water content (VWC), temperature, and relative humidity (RH).ResultsOur results showed that the variation of the VWC in the Loess Plateau is directly proportional to the amount of EVM. It is the sum of water vapor gains and losses from earth-air. Also, the amount of water in the earth-air is positively correlated with the frequency of the fluctuations in the atmospheric pressure (AP), thickness of the loess layer, aerated porosity, and gradient of the soil water vapor concentration. The correlation of recorded every 10 min for 3 years between the calculated VWC of the soil and the monitored values is 0.76.ConclusionThis study reveals a new way in which soil water migrates in the Loess Plateau and furthers our understanding of the spatiotemporal distribution mechanism. It also provides a scientific basis for the utilization of scarce water resources in semi-arid areas such as the Loess Plateau region.