DO3SE modelling of soil moisture to determine ozone flux to European forest trees

The DO₃SE (Deposition of O₃ for Stomatal Exchange) model is an established tool for estimating ozone (O₃) deposition, stomatal flux and impacts to a variety of vegetation types across Europe. It has been embedded within the EMEP (European Monitoring and Evaluation Programme) photochemical model to provide a policy tool capable of relating the flux-based risk of vegetation damage to O₃ precursor emission scenarios for use in policy formulation. A key limitation of regional flux-based risk assessments has been the assumption that soil water deficits are not limiting O₃ flux due to the unavailability of evaluated methods for modelling soil water deficits and their influence on stomatal conductance (g_sto), and subsequent O₃ flux.

This paper describes the development and evaluation of a method to estimate soil moisture status and its influence on g_sto for a variety of forest tree species. This DO₃SE soil moisture module uses the Penman-Monteith energy balance method to drive water cycling through the soil-plant atmosphere system and empirical data describing g_sto relationships with pre-dawn leaf water status to estimate the biological control of transpiration. We trial four different methods to estimate this biological control of the transpiration stream, which vary from simple methods that relate soil water content or potential directly to g_sto, to more complex methods that incorporate hydraulic resistance and plant capacitance that control water flow through the plant system.

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