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Title:   Author  item
                                            Houborg, Rasmusitem
                                            Anderson, Martha
  Submitted to: BARC Poster Day
                                    Publication Type: Abstract Only
                                    Publication Acceptance Date: 3/25/2008
                                    Publication  Date: 4/23/2008
                                    Citation: Houborg, R.M., Anderson, M.C. 2008. Validation and Intercomparison of a 'Bottom-up' and 'Top-Down' modeling paradigm for estimating energy and carbon fluxes over a variety of vegetative regimes across the U.S.[abstract]. Abs. 12, BARC Poster Day.Interpretive Summary:
                                Technical Abstract: An accurate quantification of energy and carbon fluxes is of great importance for a wide range of ecological, agricultural, and meteorological applications. Two contrasting modeling strategies are currently used widely to retrieve this goal. ‘Bottom-up’ models of land-atmosphere carbon exchange are based on detailed mechanistic descriptions of leaf-level photosynthetic processes scaled to the canopy whereas ‘top-down’ scaling approaches neglect the behavior of individual leaves and consider the canopy response to its environment in bulk. The objective of this study is to compare the analytical, light-use efficiency (LUE)-based model of canopy conductance embedded in the Atmosphere-Land Exchange (ALEX) surface energy balance model with a commonly used mechanistic model of leaf photosynthesis-stomatal response employing a two-leaf scaling strategy. ALEX is a simplified version of a detailed soil-plant-atmosphere model Cupid, specifically developed for operational applications. For the purpose of intercomparisons, the mechanistic canopy sub-model has been imbedded in ALEX. The ability of the two canopy sub-models to reproduce observed diurnal patterns in energy and carbon fluxes measured in a variety of natural and agricultural ecosystem is effectively evaluated. Comparisons were done using several years of field data compiled from AmeriFlux sites across the US. The specific advantages and disadvantages associated with each modeling strategy in the context of regional-scale flux mapping are elucidated and a sensitivity analysis is employed to establish their susceptibility to uncertainties in tunable parameter specifications.


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