Evaluating Coupled Water, Vapor, and Heat Flows and Their Influence on Moisture Dynamics in Arid Regions

Abstract

The flow and thermal driven processes are crucial for the soil water dynamics in the vadose zone in arid regions. The understanding of the soil moisture and heat distribution is important for assessing the fate and transport of contaminants for the waste-burial site in a desert setting. A coupled water, vapor, and heat flow model was used in this study for evaluating the interactions of these processes and their influence on the moisture dynamics in the Amargosa Desert Research Site (ADRS) in southern Nevada. The treatment of preferential flow was also included in the model. Data from a previously conducted tracer experiment were used for estimating initial parameters of preferential flux and the parameters in pedotransfer functions (PTFs), while the Levenberg-Marquardt algorithm was used to optimize various parameters in the model calibration on the basis of the observation data. After the model calibration, three-year simulations (1998–2000) were conducted for evaluating the spatiotemporal variability of soil moisture and temperature in the site. The simulation results show that the performance of thermal model with vapor and preferential flow is close to those of isothermal model without vapor and preferential flow as compared with the observed records in ADRS, while critical physical mechanisms could be well described with the thermal model. The vapor flow for the water budget on the upper boundary is insignificant while it influences the water content distribution in the soil profile; the wetting front depth of preferential flow and water budget has increased in rain days; however, the high evaporation counteracts it in the annual water budget. The thermal diffusion of water vapor and thermal liquid fluxes were affected by temperature fluctuation and soil water saturation status. Comparison between the flux components shows that the thermal driven flux has more weight on the water movement in the soil profile. Results indicate that the coupled flow and thermal model could well describe the natural condition in arid regions and is more efficient in simulating mutual effects among various processes.