Potential evapotranspiration viewed from the perspective of constructal theory
Abstract
In this study we investigated the evapotranspiration phenomena from the point of view of the thermodynamic constructal theory. When applied to the vegetation cover at the surface of the ground, the constructal law states that plants are adapting to gain maximum access to available resources and at the same time to minimize the internal irreversibilities of the system, that is the entropy generation rate. The analysis of plants under heat constraints showed that the optimal state of plant given potential conditions can be achieved if the optimal plant temperature defining the maximum productivity state is equal to the average air temperature which in turn has to be equal to the average vegetation temperature. To test this hypothesis, we modeled the vegetation cover as a thermodynamic system exchanging heat and mass with the atmosphere. The input data for the model were provided by the FLUXNET network. For 32 sites around the globe, we investigated the variation of the vegetation state with respect to the stomatal resistance rs. We showed that plants can thermoregulate their temperature by means of the stomatal resistance and that there is a critical stomatal resistance, rsmin, corresponding to a minimum entropy generation rate. We showed that, for sites characterized with highly evolved plants, the optimal thermodynamic state defined by rsmin is indeed selected by plants when potential condtions are met. When potential conditions are not met, plants will adapt such that the average state of vegetation will be as close as possible (given external constraints) to the optimal state defined by rsmin.
 Publication:

AGU Fall Meeting Abstracts
 Pub Date:
 December 2007
 Bibcode:
 2007AGUFM.H51H0876C
 Keywords:

 0495 Water/energy interactions (1878);
 1813 Ecohydrology;
 1818 Evapotranspiration;
 1843 Land/atmosphere interactions (1218;
 1631;
 3322);
 1878 Water/energy interactions (0495)