ARS | Publication request: Soil-water evaporation dynamics determined with measurement of sensible heat transfer

Submitted to: American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: December 14, 2007
Publication Date: December 14, 2007
Citation: Heitman, J.L., Horton, R., Sauer, T.J., Desutter, T.M. 2007. Soil-water evaporation dynamics determined with measurement of sensible heat transfer [Abstract H2ID-0744]. American Geophysical Union. 88(52).

Technical Abstract: Soil-water evaporation is important in both the hydrologic cycle and the surface energy balance. Yet, routine measurements are unable to capture rapidly shifting near-surface soil heat and water processes involved in evaporation. Recent improvements for fine-scale measurement of soil thermal properties provide new opportunity to observe soil heat transfer and soil-water evaporation in the upper centimeters of the vadose zone. Three-needle heat-pulse (HP) sensors were used to monitor soil heat capacity, thermal conductivity, water content, and temperature below a bare soil surface during a 40-d period with natural wetting/drying cycles. Soil heat flux and changes in heat storage were calculated from these data to obtain a balance of sensible heat components. The residual from this balance (i.e., the net heat flux minus the change in heat storage) was attributed to latent heat from water vaporization, and thus, provides an estimate of in situ evaporation. Fine-scale heat-pulse measurements show divergence in the near-surface sensible heat flux during drying. By accounting for the change in sensible heat storage through measurement, it is demonstrated that this divergence largely represents evaporation occurring within the soil. Observations reveal shifts in the magnitude and location of evaporation as the soil dries after rainfall. Implementation of fine-scale techniques for the measurement of soil sensible heat balance provides a new opportunity to improve understanding of evaporation dynamics and soil heat transfer in the study of a wide-range of environmental interactions. The connection between soil heat transfer and evaporation in land-atmosphere exchange should also be considered in the development of mechanistic land surface models and large-scale measurement efforts.