Preprints
https://doi.org/10.5194/gmd-2021-414
https://doi.org/10.5194/gmd-2021-414
Submitted as: development and technical paper
25 Jan 2022
Submitted as: development and technical paper | 25 Jan 2022
Status: a revised version of this preprint was accepted for the journal GMD and is expected to appear here in due course.

Implementation and evaluation of the unified stomatal optimization approach in the Functionally Assembled Terrestrial Ecosystem Simulator (FATES)

Qianyu Li1, Shawn P. Serbin1, Julien Lamour1, Kenneth J. Davidson1,2, Kim S. Ely1, and Alistair Rogers1 Qianyu Li et al.
  • 1Department of Environmental and Climate Sciences, Brookhaven National Laboratory, Upton, NY
  • 2Department of Ecology and Evolution, Stony Brook University, Stony Brook, NY

Abstract. Stomata play a central role in regulating the exchange of carbon and water vapor between ecosystems and the atmosphere. Their function is represented by land surface models (LSMs) by conductance models. The Functionally Assembled Terrestrial Ecosystem Simulator (FATES) is a dynamic vegetation demography model that can simulate both detailed plant demographic and ecophysiological dynamics. To evaluate the effect of stomatal conductance model representation on forest water and carbon fluxes in FATES, we implemented an optimality-based stomatal conductance model—the Medlyn (MED) model, that simulates the relationship between photosynthesis (A) and stomatal conductance to water vapor (gsw) as an alternative to the FATES default Ball-Woodrow-Berry (BWB) model. To evaluate how the behavior of FATES is affected by stomatal model choice, we conducted a model sensitivity analysis to explore the response of gsw to synthetic climate forcing variables including atmospheric CO2 concentration, air temperature, radiation, and vapor pressure deficit (VPD). We found that modeled gsw values varied greatly between the BWB and MED formulations due to the different default stomatal slope parameters (g1). After harmonizing g1 and holding the same stomatal intercept parameter (g0) for both model formulations, we found that the divergence in modeled gsw was limited to conditions when the VPD exceeded 1.5 kPa. We then evaluated model simulation results against measurements from a wet evergreen forest in Panama. Results showed that both the MED and BWB model formulations were able to capture the magnitude and diurnal change of measured gsw and A but underestimated both by about 30 % when the soil was predicted to be very dry. Our study suggests that the parameterization of stomatal conductance models and current model response to drought are the critical areas for improving model simulation of CO2 and water fluxes in tropical forests.

Qianyu Li et al.

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on gmd-2021-414', Anonymous Referee #1, 01 Mar 2022
  • RC2: 'Comment on gmd-2021-414', Anonymous Referee #2, 02 Mar 2022

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on gmd-2021-414', Anonymous Referee #1, 01 Mar 2022
  • RC2: 'Comment on gmd-2021-414', Anonymous Referee #2, 02 Mar 2022

Qianyu Li et al.

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Latest update: 20 May 2022
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Short summary
Stomatal conductance is the rate of water release from leaves’ pores. We implemented an optimal stomatal conductance model in a vegetation model. We then tested and compared with the existing empirical model in terms of model responses to key environmental variables. We also evaluated the model with measurements at a tropical forest site. Our study suggests that the parameterization of conductance models and current model response to drought are the critical areas for improving model simulation.