One-dimensional modeling of radiation absorption by vine canopies: Evaluation of existing model assumptions, and development of an improved generalized model

Authors: PONCE DE LEON, MARIA - University Of California, Davis; Alfieri, Joseph; Prueger, John; HIPPS, LAWRENCE - Utah State University; Kustas, William; AGAM, NURIT - Ben Gurion University Of Negev; BAMBACH, NICOLAS - University Of California, Davis; McElrone, Andrew; Knipper, Kyle; Roby, Matthew; BAILEY, BRIAN - University Of California, Davis

Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/18/2025
Publication Date: 7/18/2025
Citation: Ponce de Leon, M.A., Alfieri, J.G., Prueger, J.H., Hipps, L., Kustas, W.P., Agam, N., Bambach, N., McElrone, A.J., Knipper, K.R., Roby, M.C., Bailey, B. 2025. One-dimensional modeling of radiation absorption by vine canopies: Evaluation of existing model assumptions, and development of an improved generalized model. Agricultural and Forest Meteorology. 373. Article 110706. https://doi.org/10.1016/j.agrformet.2025.110706.
DOI: https://doi.org/10.1016/j.agrformet.2025.110706

Interpretive Summary: This study examines how well different models can simulate the way sunlight moves through vine canopies. Standard models are straightforward but may not account for the complexity and variety in canopy structure. The researchers used a more detailed model, HELIOS, along with real-world measurements in vineyards, to test simpler models that consider different canopy characteristics, like leaf density and arrangement. The findings showed that simpler models, especially those using a constant "clumping factor," didn't predict sunlight movement accurately—they tended to overestimate. A new model proposed in the study, which considers the varied structure of canopies, performed better in simulating sunlight movement through different vine canopies. This study’s results are important as they can help improve calculations related to sunlight movement in vineyards, affecting other processes like water use by plants. This improved model can be especially useful in satellite-based land and crop studies.

Technical Abstract: Land surface models typically rely on simplified one-dimensional models of radiation transfer through plant canopies to improve efficiency. Canopy heterogeneity introduces three-dimensional effects that are difficult to represent within simple models. Model validation is complicated by the difficulty of measuring large-scale radiation transfer in complex, heterogeneous environments. In this study, simple models considering a clumping factor and geometric approaches were evaluated with the aid of a three-dimensional leaf-resolving radiation model, HELIOS, and field measurements in vine canopies. A range of heterogeneous canopies with a rectangular prism crown shape and with varying leaf area index, spacing, trellis system, and leaf angle distributions were generated and used to isolate various model assumptions. Results showed that assuming a constant clumping factor and attenuation coefficient considerably over-predicted radiation transfer for all canopy cases. Assuming a constant clumping factor resulted in large errors. For the variable clumping factor model, errors increased significantly when the path length through vegetation was not correctly represented. Compared to the clumping factor models, the proposed geometric binomial model accounts for the variable path length through vegetation and multiple crown intersections, resulting in small errors for these heterogeneous canopies. With some additional inputs related to the canopy structure, this scheme could be incorporated in crop models, terrestrial ecosystem models and land surface models, particularly those based on satellite remote sensing data. Results of this work provide quantitative guidance to improve the calculation of radiation transfer in vineyards and, thus, other dependent biophysical processes such as evapotranspiration and its partitioning into soil evaporation and plant transpiration.