An Application of the Theory of Maximum Entropy Production in Modeling Evapotranspiration

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An Application of the Theory of Maximum Entropy Production in ModelingEvapotranspiration(NSF Proposal 0943356)PIs: Rafael L. Bras and Jingfeng WangUniversity of California, IrvineAbstractThis project aims at developing an innovative model of evapotranspiration (ET) over land surfaces based on the theory of maximum entropy production (MEP), an emerging theoretical framework for non-equilibrium systems. The effort is guided by promising preliminary results that obtained expressions for ground and sensible heat fluxes over a dry land surface. The research is organized in: (1) theoretical development and (2) observational validation. The central task of the theoretical development is to formulate, based on our best understanding of the turbulent transport in the atmospheric boundary layer (ABL), an expression for the ?thermal inertia for transferring latent heat? that is the key parameter of the dissipation function whose extremization leads to the MEP solution of latent, sensible and ground heat fluxes. We follow three leads in formulating the ?thermal inertia for latent heat?: (1) the turbulent mixing responsible for the transport of sensible heat in the ABL is also responsible for the transport of water vapor, (2) water vapor right above the evaporating surface is in equilibrium with the soil water, and (3) the surface variables of temperature and humidity (as well as stomatal conductance over the canopy) are sufficient to determine the energetics of the evapotranspiration. As a result, the ?thermal inertia for transferring latent heat? is expected to be a function of surface temperature and humidity (and stomatal conductance) for the case of bare soil (canopy). The validation phase of the project has a two-fold objective: (1) validating the MEP model of ET for bare soil and canopy at local scales, and (2) exploring a possible application of the MEP model of ET formulated at local scale (defined as the scales at which the Monin-Obukhov turbulence model applies) to regional scales. Validation of the MEP model at local scales will mostly use archived datasets from previous field campaigns supplemented by additional field measurements whenever needed. Test of the MEP model of ET at regional scales will compare latent, sensible, and ground heat fluxes predicted by the MEP model with the reanalysis datasets using other ET models. Depending on progress, the theoretical development may expand to include the case of water (oceans, lakes, etc.) and snow surfaces. The project, if successfully carried out, will provide a new modeling framework for predicting the land surface energy balance at local scales and hopefully producing improved datasets of surface heat fluxes with global coverage.If successful the results of this effort will provide a completely new method to compute the land surface energy balance that would be parsimonious and require little calibration. The method will be implemented in existing land surface models that are used to make hydro-climatic predictions. Besides engaging doctoral students in the effort, the project will use an existing undergraduate research opportunities program to engage at least one undergraduate student, preferably from a disadvantaged group, in learning energy and hydrologic balances by performing field experiments that could yield supporting data sets. A complete set of instruments to measure energy fluxes and temperature, soil moisture and other hydrologic variables required are available. All students, graduate and undergraduate, will be engaged in presenting their results in appropriate scientific meetings and journals. The University publishes a research journal for undergraduates. The senior investigator is a leader, host and participant of the MESA and CAMP outreach programs housed at the school of engineering of the University of California, Irvine. This provides access to underprivileged students in middle and high schools as well as community colleges. This access will be used to engage interested participants in issues related to hydrology and earth sciences. Mechanisms include visits to schools, receiving students at the university, giving public lectures and sponsoring or supervising project work.