A 3D Canopy Radiative Transfer Model for Global Climate Modeling: Description, Validation, and Application

The process of solar radiative transfer at the land surface is important to energy, water, and carbon balance, especially for vegetated areas. Currently the most commonly used two-stream model considers the plant functional types (PFTs) within a grid to be independent of each other and their leaves...

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Bibliographic Details
Published in:Journal of climate 2014-02, Vol.27 (3), p.1168-1192
Main Authors: Yuan, Hua, Dickinson, Robert E., Dai, Yongjiu, Shaikh, Muhammad J., Zhou, Liming, Shangguan, Wei, Ji, Duoying
Format: Article
Language:English
Subjects:
Absorption
Albedo
Canopies
Canopy
Climate models
Climatology. Bioclimatology. Climate change
Earth, ocean, space
Ecological modeling
Exact sciences and technology
External geophysics
Forest canopy
Geophysics. Techniques, methods, instrumentation and models
Global climate
Global climate models
Incident radiation
Leaves
Meteorology
Modeling
Modelling
Multilayers
Numerical simulations
Optical properties
Plant cover
Radiation
Radiative transfer
Remote sensing
Rivers
Shadows
Shape
Shape effects
Three dimensional modeling
Three dimensional models
Vegetation
Vegetation canopies
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Summary:The process of solar radiative transfer at the land surface is important to energy, water, and carbon balance, especially for vegetated areas. Currently the most commonly used two-stream model considers the plant functional types (PFTs) within a grid to be independent of each other and their leaves to be horizontally homogeneous. This assumption is unrealistic in most cases. To consider canopy three-dimensional (3D) structural effects, a new framework of 3D canopy radiative transfer model was developed and validated by numerical simulations and shows a good agreement. A comparison with the two-stream model in the offline Community Land Model (CLM4.0) shows that an increase of canopy absorption mainly happens with sparse vegetation or with multilayer canopies with a large sun zenith angleθ sunand is due to increases of the ground and sky shadows and of the optical pathlength because of the shadow overlapping between bushes and canopy layers. A decrease of canopy absorption occurs in densely vegetated areas with smallθ sun. For a one-layer canopy, these decreases are due to crown shape effects that enhance the transmission through the canopy edge. For a multilayer canopy, aside from these shape effects, transmission is also increased by the decreased ground shadow due to the shadow overlapping between layers. Ground absorption usually changes with opposite sign as that of the canopy absorption. Somewhat lower albedos are found over most vegetated areas throughout the year. The 3D model also affects the calculation of the fraction of sunlit leaves and their corresponding absorption.
ISSN:0894-8755
1520-0442
DOI:10.1175/JCLI-D-13-00155.1