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Evapotranspiration Remote Sensing and Modeling Part 15

Tham khảo tài liệu 'evapotranspiration remote sensing and modeling part 15', khoa học tự nhiên, công nghệ sinh học phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Stomatal Conductance Modeling to Estimate the Evapotranspiration of Natural and Agricultural Ecosystems 409 for the transpiration rate E the hyperbolic function of VPDs is equivalent to a linear decline of gs with increasing E. The main limitation of the Ball-Berry-Leuning BBL model is its failure in describing stomatal closure in drought conditions. The model has been further implemented by Dewar 2002 to take SWC in consideration by coupling the BBL model with Tardieu model for stomatal response to drought. The coupled model takes the form gs a11 AnviRd exPị- ABA exp ổT 12 Ci I 1 VPDo I VPDs Where Rd is dark respiration ABA is the concentration of abscisic acid in the leaf xylem T is the leaf water potential p is the basal sensitivity of ion diffusion to ABA at zero leaf water potential and s describes the increase in the sensitivity of ion diffusion to ABA as T declines. The model has the advantage of describing stomatal responses to both atmospheric and soil variables and has proven to reproduce a number of common water use trends reported in the literature as for example isohydric and anisohydric behaviour. 4. Modelling water vapour exchange between leaves and atmosphere and scaling it up to plant and ecosystem level The big-leaf approach and the resistive analogy The exchange of water vapour through stomata is a molecular diffusion process since air in the sub-stomatal cavities is motionless as well as the air in the first layer outside the stomata directly in contact with the outer leaf surface i.e. the leaf boundary-layer . Outside the leaf boundary-layer it is the turbulent movement of air that removes water vapour and this process is two orders of magnitude more efficient than the molecular diffusion. The exchange of water between the plant and the atmosphere is further complicated by the physiological control that stomatal resistance exerts on the diffusion of water vapour to the atmosphere. Transpiration is modelled through an electric analogy Ohm s law