wiki:GroupActivities/CodeAvalaibilityPublication/ORCHIDEE_2.2_gmd_2022

ORCHIDEE_2.2

This version of ORCHIDEE has been used in publication "Evaluating the vegetation-atmosphere coupling strength of ORCHIDEE land surface model (v7266)" by Zhang et al to be submitted to GMD. Reference and information will be added later << Reference to be added as soon as the manuscript is available >>.

Abstract

Plant transpiration dominates terrestrial evapotranspiration (ET) and plays a central role in regulating the water cycle and land surface energy budget. However, currently Earth system models (ESM) disagree strongly on the amount of transpiration, and thus ET, leading to large uncertainties in simulating future climate. Thus it is crucial to correctly represent the mechanisms controls of the transpiration in models. At the leaf-scale, transpiration is controlled by stomatal regulation, and at the canopy-scale, through turbulence (“roughness”) which is a function of canopy structure and wind. The coupling of vegetation to the atmosphere can be characterized by a coefficient Ω. A value of Ω → 0 implies a strong coupling of vegetation and the atmosphere, leaving a dominant role to stomatal conductance in regulating water (H2O) and carbon dioxide (CO2) fluxes, while Ω → 1 implies a complete decoupling of leaves from the atmosphere, that is, the transfer of H2O and CO2 is limited by aerodynamic transport. In this study, we investigated how well the land surface model ORCHIDEE (v7266), simulates the coupling of vegetation to the atmosphere by using empirical daily estimates of Ω derived from flux measurements from 106 FLUXNET sites. Our results show that ORCHIDEE generally captured the Ω in forest vegetation types (0.27±0.10) compared with observation (0.26±0.09), but underestimated Ω in grasslands and croplands (0.26±0.16 for model, 0.33±0.17 for observation). However, the good model performance in forest Ω is due to compensation of biases in surface (Gs) and aerodynamic conductance (Ga). Calibration of key parameters controlling the dependence of the stomatal conductance to the water vapor deficit (VPD) improved the simulated Gs, and improved the Ω estimates grasslands and croplands (0.30±0.21). To assess the underlying controls of Ω, we applied random forest (RF) models to both simulated and observation-based Ω. We found that high observed Ω are associated with periods of low wind speed, high temperature, low VPD and related to sites with high leaf area index (LAI) and/or short vegetation. The RF models applied to ORCHIDEE output generally agree with this pattern. However, we found the ORCHIDEE underestimated the sensitivity of Ω to VPD when VPD is high, overestimated the impact of LAI (i.e., too rough), and did not correctly simulate the temperature dependence of Ω when temperature is high. Our results highlight the importance of observational constraints on simulating the vegetation-atmosphere coupling strength, which can help improve the predictive accuracy of water fluxes in Earth system models.

Code access

Metadata

DOI [under request]
Creator Yuan ZHANG
Affiliation LSCE
Title ORCHIDEE_2.2
Publisher Institut Pierre Simon Laplace (IPSL)
PublicationYear 2022
ResourceType Software
Rights This software is distributed under the CeCILL license
rightsURI ​http://www.cecill.info/
Subject Canopy light transmission, Land surface model, terrestrial carbon cycle
DataManager Karim Ramage (IPSL)
DataCurator Josefine Ghattas (IPSL)
ContactPerson Yuan Zhang (LSCE)
FundingReference to be added

Last modified 2 years ago Last modified on 2022-05-18T15:29:28+02:00