Spatio-temporal dynamics of water and heat in a field soil

Soil water content (theta)and soil temperature (T) near the land-atmosphere boundary interactively govern upward and downward fluxes of water and energy. To date few if any comprehensive studies have examined the spatio-temporal variability and interactive relationships between theta and T at the field-scale. This information is required for held-scale modeling of nonisothermal water, heat, and chemical transport in soil. As well, it may prove useful for modeling the near-surface atmosphere component of General Circulation Models and addressing related scale issues. The objectives of this study were to (i) simultaneously monitor, with high temporal resolution, the soil water content and soil temperature at a large number of spatial locations and depths in a field under different soil moisture conditions, and (ii) study the spatio-temporal variability and functional correlation of the two state variables theta and T at the field-scale. Soil water content and soil temperature measurements were made at 20 min intervals at 49 regularly-spaced (1.0 m) locations and at 3 depths along two transects in a bare held in Riverside, California. Measurements were made for a period of 45 days during different irrigation events. More than 150 TDR probes and 150 thermocouples were used in conjunction with 25 multiplexers and several data loggers for automatic monitoring. Correlation analysis of the data revealed a diurnal spatio-temporal hysteresis in the mean and variance of T during dry and wet days. Corresponding theta-values did not exhibit much spatio-temporal hysteresis, although they had a tendency to cluster across time at different depths. (C) 1998 Elsevier Science B.V. All rights reserved.