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Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/gmd-2020-96
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/gmd-2020-96
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: model description paper 18 Jun 2020

Submitted as: model description paper | 18 Jun 2020

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A revised version of this preprint is currently under review for the journal GMD.

Modeling the impacts of diffuse light fraction on photosynthesis in ORCHIDEE (v5453) land surface model

Yuan Zhang1,2, Ana Bastos3, Fabienne Maignan2, Daniel Goll4, Olivier Boucher5, Laurent Li1, Alessandro Cescatti6, Nicolas Vuichard2, Xiuzhi Chen7, Christof Ammann8, Altaf Arain9, T. Andrew Black10, Bogdan Chojnicki11, Tomomichi Kato12,13, Ivan Mammarella14, Leonardo Montagnani15,16, Olivier Roupsard17,18,19, Maria J. Sanz20,21, Lukas Siebicke22, Marek Urbaniak11, Francesco Primo Vaccari23, Georg Wohlfahrt24, Will Woodgate25,26, and Philippe Ciais2 Yuan Zhang et al.
  • 1Laboratoire de Météorologie Dynamique, IPSL, Sorbonne Université/CNRS, Paris, France
  • 2Laboratoire des Sciences du Climat et de l'Environnement (LSCE), IPSL, CEA/CNRS/UVSQ, Gif sur Yvette, France
  • 3Department of Geography, Ludwig–Maximilian University of Munich, Munich, Germany
  • 4Department of Geography, University of Augsburg, Augsburg, Germany
  • 5Institut Pierre–Simon Laplace, CNRS/Sorbonne Université, Paris, France
  • 6Institute for Environment and Sustainability, Joint Research Centre, European Commission, Ispra, Italy
  • 7Guangdong Province Key Laboratory for Climate Change and Natural Disaster Studies, School of Atmospheric Sciences, Sun Yat-sen University, Guangzhou 510275, China
  • 8Climate and Agriculture Group, Agroscope, Zürich, 8046, Switzerland
  • 9School of Geography and Earth Sciences and McMaster Centre for Climate Change, McMaster University, Hamilton, ON, Canada
  • 10Faculty of Land and Food Systems, University of British Columbia, Vancouver, BC, Canada
  • 11Poznan University of Life Sciences, Piatkowska 94, 60-649 Poznan, Poland
  • 12Research Faculty of Agriculture, Hokkaido University, Sapporo 060-8589, Japan
  • 13Global Institution for Collaborative Research and Education, Hokkaido University, Sapporo 060-8589, Japan
  • 14Institute for Atmospheric and Earth System Research/Physics, Faculty of Sciences, University of Helsinki, Finland
  • 15Autonomous Province of Bolzano, Forest Services, Via Brennero 6, Bolzano 39100, Italy
  • 16Faculty of Science and Technology, Free University of Bolzano, Piazza Università 5, Bolzano 39100, Italy
  • 17CIRAD, UMR Eco&Sols, BP1386, CP18524, Dakar, Senegal
  • 18Eco&Sols, Univ Montpellier, CIRAD, INRAE, IRD, Montpellier SupAgro, Montpellier, France
  • 19LMI IESOL, Centre IRD-ISRA de Bel Air, BP1386, CP18524 Dakar, Senega
  • 20Basque Centre for Climate Change, Sede Building 1, Scientific Campus of the University of the Basque Country, 48940, Leioa, Spain
  • 21Ikerbasque, Basque Science Foundation, 48013 Bilbao, Spain
  • 22University of Goettingen, Bioclimatology, Büsgenweg 2, 37077 Göttingen, Germany
  • 23Institute of BioEconomy, National Research Council, 50145 Firenze, Italy
  • 24Department of Ecology, University of Innsbruck, Innsbruck, Austria
  • 25CSIRO Land & Water, Canberra, ACT, Australia
  • 26School of Earth and Environmental Sciences, University of Queensland, St Lucia, 4067, Qld, Australia

Abstract. Aerosol and cloud-induced changes in diffuse light have important impacts on the global land carbon cycle by changing light distribution and photosynthesis in vegetation canopies. However, this effect remains poorly represented in current land surface models. Here we add a light partitioning module and a new canopy light transmission module to the ORCHIDEE land surface model (trunk version, v5453) and use the revised model, ORCHIDEE_DF, to estimate the fraction of diffuse light and its effect on gross primary production (GPP) in a multi-layer canopy. We evaluate the new parameterizations using flux observations from 159 eddy covariance sites over the globe. Our results show that compared to the original model, ORCHIDEE_DF improves the GPP simulation under sunny conditions and captures the observed higher photosynthesis under cloudier conditions in most plant functional types (PFTs). Our results also indicate that the larger GPP under cloudy conditions compared to sunny conditions is mainly driven by increased diffuse light in the morning and in the afternoon, and by decreased VPD and air temperature at midday. The observations show strongest positive effects of diffuse light on photosynthesis are found in the range 5–20 °C and VPD < 1 kPa. This effect is found to decrease when VPD becomes too large, or temperature falls outside that range likely because of increasing stomatal resistance to leaf CO2 uptake. ORCHIDEE_DF underestimates the diffuse light effect at low temperature in all PFTs and overestimates this effect at high temperature and high VPD in grasslands and croplands. The new model has the potential to better investigate the impact of large-scale aerosol changes on the terrestrial carbon budget, both in the historical period and in the context of future air quality policies and/or climate engineering.

Yuan Zhang et al.

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Model code and software

ORCHIDEE_DFv1.0_site Y. ZHANG https://doi.org/10.14768/20200407003.1

Yuan Zhang et al.

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Latest update: 22 Sep 2020
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Short summary
We improved the ORCHIDEE LSM by distinguishing diffuse and direct light in canopy and evaluated the new model with observations from 159 sites. Compared with the old model, the new model has better sunny GPP and reproduced the diffuse light fertilization effect observed at flux sites. Our simulations also indicate different mechanisms causing the observed GPP enhancement under cloudy conditions at different time. The new model has the potential to study large scale impacts of aerosol changes.
We improved the ORCHIDEE LSM by distinguishing diffuse and direct light in canopy and evaluated...
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