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Influence of sun zenith angle on canopy clumping and the resulting impacts on photosynthesis

Braghiere, Renato K. and Quaife, Tristan and Black, Emily and Ryu, Youngryel and Chen, Qi and De Kauwe, Martin G. and Baldocchi, Dennis (2020) Influence of sun zenith angle on canopy clumping and the resulting impacts on photosynthesis. Agricultural and Forest Meteorology, 291 . Art. No. 108065. ISSN 0168-1923.

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Addressing the impact of vegetation architecture on shortwave radiation transfer in land surface models is important for accurate weather forecasting, carbon budget estimates, and climate predictions. This paper investigates to what extent it is possible to retrieve structural parameters of two different parameterization schemes from direct transmittance derived from digital hemispherical photography and 3D radiative transfer modeling for two study sites with different vegetation canopy architectures. Neglecting the representation of 3D canopy structure in radiative transfer schemes leads to significant errors in shortwave radiation partitioning (up to 3.5 times more direct transmittance in the 3D model). Structural parameters, referred to as whole canopy ‘clumping indices’, were obtained in order to evaluate the impact of angular variation in clumping on shortwave radiation transfer. Impacts on photosynthesis were evaluated at site level with the UKESM land surface model, JULES. A comparison between flux tower derived and modeled photosynthesis indicates that considering zenith angular variations of structural parameters in the radiative transfer scheme of the UKESM land surface model significantly improves photosynthesis prediction in light limited ecosystems (from RMSE = 2.91 μmol CO₂.m⁻².s⁻¹ to RMSE = 1.51 μmol CO₂.m⁻².s⁻¹, 48% smaller), typically with enhanced photosynthesis from bottom layers.

Item Type:Article
Related URLs:
URLURL TypeDescription
Braghiere, Renato K.0000-0002-7722-717X
Quaife, Tristan0000-0001-6896-4613
Black, Emily0000-0003-1344-6186
Ryu, Youngryel0000-0001-6238-2479
De Kauwe, Martin G.0000-0002-3399-9098
Baldocchi, Dennis0000-0003-3496-4919
Additional Information:© 2020 Elsevier B.V. Received 9 October 2019, Revised 23 May 2020, Accepted 31 May 2020, Available online 12 June 2020. This work was partly conducted during a PhD scholarship supported by the ‘Science without Borders’ Program at the University of Reading (grant number 9549-13-7). Financed by CAPES – Brazilian Federal Agency for Support and Evaluation of Graduate Education within the Ministry of Education of Brazil. This research was carried out in part at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. California Institute of Technology. Government sponsorship acknowledged. This material is based upon work partly supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Terrestrial Ecosystem Science program under Award Numbers DE-SC0008317 and DE-SC0016188. Funding was also provided by the NASA IDS program. Copyright 2020. All rights reserved. Tristan Quaife's contribution was funded by the NERC National center for Earth Observation. The authors would like to thank Pier-Luigi Vidale, Sue Grimmond, and Peter North for discussions on radiative transfer and carbon budget. A UNIX patch file for JULES version 4.6 is available from The JULES code is available from the UK Met Office code repository: Model simulation results were made available with this publication. The authors thank three anonymous reviewers whose comments improved the manuscript. Declaration of Competing Interest: None.
Funding AgencyGrant Number
University of Reading9549-13-7
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)UNSPECIFIED
Department of Energy (DOE)DE-SC0008317
Department of Energy (DOE)DE-SC0016188
Subject Keywords:Vegetation canopy architecture; Vegetation structure; Clumping index; Gross primary productivity; Radiative transfer schemes; Digital hemispherical photography; Parameterization schemes
Record Number:CaltechAUTHORS:20200904-094141081
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Official Citation:Renato K. Braghiere, Tristan Quaife, Emily Black, Youngryel Ryu, Qi Chen, Martin G. De Kauwe, Dennis Baldocchi, Influence of sun zenith angle on canopy clumping and the resulting impacts on photosynthesis, Agricultural and Forest Meteorology, Volume 291, 2020, 108065, ISSN 0168-1923, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:105259
Deposited By: Renato Braghiere
Deposited On:08 Sep 2020 16:47
Last Modified:08 Sep 2020 17:16

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