Evapotranspiration over Land from a Boundary-Layer Meteorology Perspective
Cuxart, J. ; Boone, Aaron A.
Correction to: Evapotranspiration over Land from a Boundary-Layer Meteorology Perspective
The precise determination of evapotranspiration rate is challenging because it is a quantity that is difficult to measure and to parametrize. Direct estimates include the determination of the change of mass of a volume of soil and vegetation that evapotranspirates using lysimeters, or direct measurements of turbulent water vapour fluxes by eddy-covariance systems. Parametrized estimates that make use of the Monin-Obukhov similarity theory use vertical gradient measurements of temperature and moisture at one point, and line or area averages by means of scintillometers operating at high frequency. A relation for the evapotranspiration from well-watered surfaces was initially developed by Penman and later expanded for vegetated surfaces and for heterogeneous croplands. A popular simplified expression was obtained by Priestley and Taylor. The current challenge is to find expressions for the evapotranspiration in non-saturated conditions, which are common in arid and semi-arid climates, and for heterogeneous terrain. In numerical models, the estimated actual evapotranspiration over land is obtained as the result of the explicit representation of the different involved sub-processes taking place in the soil and the canopy, using so-called land-surface models. Usually these mechanisms are described in a simplified manner and rely on a number of adjustable parameters. The improvement of such descriptions relies in the availability of experimental measurements to make the physical models more complete and robust.</p>
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