Integration of Heat-Pulse and Sensible Heat Balance Methods to Estimate Evaporation From Bare Soils

A critical component of the water cycle at local, regional and global scales is evaporation from soil. Because it is very difficult to measure soil evaporation and soil moisture in the field, with the exception of using a lysimeter for local measurements, numerous model based estimation methods have been proposed. Numerical approaches that attempt to estimate evaporation rates within the top several centimeters of soil often rely of empirical and semi-empirical methods. Another less well known method to determine evaporation relies on heat pulse sensors to measure soil temperature and thermal properties. This approach does not rely on knowledge of soil hydraulic properties, effectively removing the need of several common empirical methods to define the soil surface boundary condition. The objective of this study was to integrate both the heat-pulse and sensible heat balance methods into a non-isothermal multiphase flow model in order to define the boundary conditions at the land/atmosphere interface. This model was tested using precision experimental data collected under laboratory conditions and compared to more traditional numerical modeling approaches. Experimental data was generated in a two-dimensional soil tank containing an array of sensors that allowed soil temperature, soil moisture content, and relative humidity to be collected continuously and autonomously. The soil tank was placed within a wind tunnel test facility to insure that atmospheric conditions were carefully controlled and monitored throughout the duration of the experiment. Numerical results of the model using the heat pulse and sensible heat balance methods were compared to those generated using different, more traditional modeling approaches. Results demonstrate the applicability of incorporating the heat-pulse and sensible heat balance methods in numerical approaches. Further validation was provided through a comparison of the numerical results and independently determined experimental results. This numerical approach shows great ability to accurately predict soil-water evaporation rates at fine spatial and temporal scales. Results of this study will be used in future research for larger, more complex atmospheric conditions and soil heterogeneities.