Submitted to: Vadose Zone Hydrol
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/1/1999
Publication Date: N/A
Citation: Interpretive Summary: New approaches to the measurement of field and regional scale evaporation were evaluated through field experimentation and modeling. The field scale techniques utilize atmospheric measurements rather than point values of soils and plants thus providing integrated measurements. Regional extrapolations are explored through the use of passive microwave remote sensing of soil moisture in models. Better information on evaporation is critical to understanding hydrologic processes at the field scale and scaling this to regional, continental, and global level is a major issue for quantifying the effects of climate change on hydrology.
Technical Abstract: The measurement and modeling of field or regional scale evaporation is essential to all land surface water budget calculations. Much hydrologic evaporation research concerns the development of empirical, site specific surface resistance formulations which relay on some measure of surface aridity. Passive microwave remote sensing may provide large scale measures of near surface soil moisture for use in resistance evaporation formulations; however, these evaporation formulation require significantly more research before they are useful for actual calculation purposes. Perhaps the most promising approach to obtain field or region scale surface fluxes is to take advantage of the integrating power of the turbulent atmosphere, rather than relying on point measures of soil or plant properties since the lengths scales in the boundary layer are orders of magnitude larger than length scales found in surface soils and the turbulent flow provides a natural spatial integration. Two boundary layer approaches for measuring surface heat fluxes are given here. A new one step flux dissipation method for sensible hear (H) and latent hear (LcE) is discussed., The main advantage of the dissipation method over direct eddy correlation is that the alignment of the probes in the field is less important. Also, a new one point Bowen ratio method is presented to obtain H and LcE without the requirement for measurements of surface available energy (Qnc) or atmospheric temperature and humidity gradients.