Evaporation from Heterogeneous and Sparse Canopies: On the Formulations Related to Multi-Source Representations |
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| Authors: | J P Lhomme C Montes F Jacob L Prévot |
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| Institution: | (1) Centro de Investigaci?n y Transferencia en Riego y Agroclimatolog?a (CITRA), Facultad de Ciencias Agrarias, Universidad de Talca, Casilla 747, Talca, Chile;(2) Institut National de la Recherche Agronomique (INRA), Unit? Climat, Sol et Environnement, Domaine St. Paul, Site Agroparc, 84914 Avignon Cedex 9, France |
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| Abstract: | Evaporation from heterogeneous and sparse canopies is often represented by multi-source models that take the form of electrical
analogues based upon resistance networks. The chosen representation de facto imposes a specific form on the composition of
elementary fluxes and resistances. The two- and three-source representations are discussed in relation to previous work where
some ambiguities arise. Using the two-layer model (Shuttleworth and Wallace, Q J R Meteorol Soc 111:839–855, 1985) and the clumped (three-source) model (Brenner and Incoll, Agric For Meteorol 84:187–205, 1997) as a basis, it is shown that the stomatal characteristics of the foliage (amphistomatous or hypostomatous) generate different
formulations. New generic and more concise equations, valid in both configurations, are derived. The differences between the
patch and layer approaches are outlined and the consequences they have on the composition and formulation of component fluxes
are specified. Then, the issue of calculating the effective resistances of the single-layer model from multi-source representations
is addressed. Finally, a sensitivity analysis is carried out to illustrate the significance of the new formulations. |
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