Coupled Dynamics in Soil: Understanding the Transport Mechanism of Liquid Water, Water Vapor, Dry Air and Heat by Field Experiments and Numerical Simulation

i Acknowledgements This story may track back to a discussion between Prof. Bob Su and Prof. Li Wan about a phenomenon they found from a satellite map, from which they found the upward latent heat flux at night. To understand that seeming conflict to the normal knowledge of evaporation, Prof. Li Wan and Wenbing Cao from Chinese University of Geosciences (Beijing) conducted a field experiment on a sand dune located in Gansu Province, North Western China. The experiment was designed to check if there is a loss of soil water content at night. The result of that experiment convinced Prof. Wan to continue this topic. I was one of the main investigators involved in this interesting topic. Prof. Wan was a visionary promotor to self-finance me to carry out several experiments for understanding the phenomenon. The preliminary experimental results suggested that the coupled moisture and heat transport in the soil should be the key to explain the phenomenon. In 2007, I was fortunate to have Bob Su as my promotor and supervisor, who offered me a PhD scholarship to dig deeper in this topic. Since then, my research had been being on a platform I cannot reach before, with the strong and robust supports and guidance. After the qualification, I was linked to Prof. Jun Wen to do the field work in the Badain Jaran Desert, where people can find a unique landscape of coexisting sand dunes and lakes. Such unique landscape had been attracting continuous attentions from hydrologists to investigate the water cycle in the desert, where the soil water dynamics in the unsaturated soil is characterized by the dominant vapor transport. This represents the extremely strong coupled moisture and heat transport process in the soil. The understanding of the soil water dynamics in such area may explain the phenomenon mentioned in the first paragraph. Although many difficulties stood before conducting an in-situ measurement in the Badain Jaren desert, Prof. Su, Prof. Wen and Prof. Wan gave their full supports for this experiment. Fortunately, their support finally took me to present this dissertation. As can be understood from its involved origin, this dissertation required the help from many people, whom I gratefully remember. I owe my deepest gratitude to Prof. Li Wan for his patient and constructive suggestion and guidance at the beginning of the research. He is the professor ii who introduced me how to do the research …