[A-HW18] Hydrology & Water Environment

[AHW18-P02] Estimating solar radiation exposure on the canopy and evaluating transpiration of Japanese cypress forest

*Xinwei Wang¹, Takashi Gomi¹, Kotani Ayumi¹, ChanWei Chiu², Yusuke Mizuuchi³ (1.Nagoya University Graduate School of Bioagricultural Sciences, 2. Tsukuba University School of Life and Eniornimental Science, 3.University of Tokyo Forests Ecohydrology Research Institute)

Keywords:Transpiration, Solar Radiation, 3D canopy modeling, Sap flow

Transpiration is a vital process in forests, facilitating the release of water vapor from the tree canopy into the atmosphere through stoma. It serves as a significant pathway for water transfer from the surface to the atmosphere. Current measurement techniques for single-tree sap flow are very useful for studying transpiration and are not affected by spatial heterogeneity of topography, especially in countries such as Japan, where mountainous forests make up a much larger proportion of the forest. However, scaling up the proportion of sap flow from a single tree to an entire forest can lead to errors. This study at the Ecohydrology Research Institute of the University of Tokyo Forests, focused on a 37-year-old Japanese cypress forest. The study used an unmanned aerial vehicle (UAV) for 3D canopy modeling and sap flow monitoring with the aim of (1) estimating radiation exposure of the canopy and (2) assessing sap flow in relation to canopy structure.
The 3D model simulated Solar Radiation duration and distribution. Sap flow measurements based on the Granier method with weather data from the nearby station were analyzed. It was shown that distribution of incident solar radiation on individual tree crowns is affected by the structure of adjacent tree crowns. In turn, sap flow responds differently to different orientations, which is likely related to differences in the distribution of solar radiation in the direction. These preliminary insights emphasize the need for further research to validate the findings and understand the mechanisms of water transport in trees under changing environmental conditions.