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Implementing a plant hydraulics parameterization in the Canadian Land Surface Scheme Including biogeochemical Cycles (CLASSIC) v.1.4
  • +6
  • Muhammad Umair,
  • Joe R. Melton,
  • Alexandre Roy,
  • Cleiton Breder Eller,
  • Jennifer Lynn Baltzer,
  • Bram Hadiwijaya,
  • bo qu,
  • Nia Perron,
  • Oliver Sonnentag
Muhammad Umair
Universite de Montreal

Corresponding Author:[email protected]

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Joe R. Melton
Environment Canada
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Alexandre Roy
Université du Québec à Trois-Rivières
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Cleiton Breder Eller
University of Exeter
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Jennifer Lynn Baltzer
Wilfrid Laurier University
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Bram Hadiwijaya
Deaprtment of Sustainability Research, SMART Research Institute
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bo qu
Université de Montréal
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Nia Perron
Université de Montréal
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Oliver Sonnentag
Université de Montréal
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Abstract

Drought conditions caused by soil moisture stress and/or high vapour pressure deficit pose a challenge to many terrestrial ecosystem models (TEMs). The Canadian LAnd Surface Scheme Including biogeochemical Cycles (CLASSIC) employs an empirical approach to link soil moisture stress with stomatal conductance. Such soil moisture-based empirical approaches typically perform poorly during drought. Here, we implemented an explicit plant hydraulics parameterization, i.e., Stomatal Optimization based on Xylem hydraulics (SOX), in CLASSIC, thereby connecting the soil-plant-atmosphere continuum through plant hydraulic traits. Performance of the resulting CLASSIC$_{SOX}$ was evaluated against carbon and water fluxes measured with eddy covariance at eight boreal forest flux tower sites in North America. Compared to CLASSIC, CLASSIC$_{SOX}$ better simulated gross primary productivity (GPP) across all sites, i.e., coefficient of determination (R$^{2}$) increased (0.51 to 0.59), root mean square error (RMSE) and bias decreased (1.85 to 1.54 g C m$^{-2}$ d$^{-1}$) and (-0.99 to -0.58 g C m$^{-2}$ d$^{-1}$), respectively. Under drought conditions, identified using the Palmer drought severity index, GPP simulated with CLASSIC$_{SOX}$ improved compared to CLASSIC, i.e., R$^{2}$ increased (0.51 to 0.60), and RMSE and bias decreased (1.79 to 1.46 g C m$^{-2}$ d$^{-1}$) and (-0.97 to -0.53 g C m$^{-2}$ d$^{-1}$), respectively. In contrast, CLASSIC$_{SOX}$ simulated evapotranspiration worsened, i.e., R$^{2}$ decreased (0.61 to 0.42), RMSE increased (0.54 to 0.62 mm d$^{-1}$), and bias changed direction (0.09 to -0.09 mm d$^{-1}$). As evaporation is a highly parameterized process in CLASSIC, it likely needs to be re-parameterized to account for the SOX transpiration behaviour.