Experimental Evaluation of Heat Pulse Energy Balance Approach for Measuring Transient Evaporation.

Soil-limited evaporation is difficult to measure or estimate. Deeper understanding of soil-limited evaporation requires detailed investigation of the highly dynamic near-surface zone. Recent research suggests the potential for a sensible energy balance approach to estimate latent heat fluxes from evaporation. Multi-needle heat-pulse probes have the capability to continuously measure near-surface temperature and thermal property profiles at the mm scale necessary to determine the sensible energy balance. These detailed fine-scale measurements can be used to continuously monitor magnitude and depth of transient subsurface evaporation. Full realization of this approach, however, requires further testing and evaluation. We are conducting experiments with objectives to (1) evaluate the heat-pulse energy-balance approach for measuring transient evaporation by comparing it with mass balance under controlled laboratory conditions, and (2) to study the effect of boundary layer conditions on depth and magnitude of subsurface soil water evaporation. Experimental data comparing evaporation estimated using heat-pulse energy-balance approach with mass-balance approach under transient evaporation conditions will be presented.