3D plant modeling to better assess heat impacts on vegetation in heterogeneous microclimates.

To address climate change and the growing frequency of heatwaves and droughts, several dual-land solutions have been proposed - including agroforestry, agrivoltaics, and downstream hedgerow systems - which integrate trees, photovoltaic panels, or hedgerows with agricultural crops. At a short time scale, such configurations protect crops from excessive sunlight and strong winds, while at a longer time scale, they improve water conservation, thus enhancing crop thermoregulation during heatwaves and droughts (Barron-Gafford, et al., 2019). To accurately predict the level of protection provided, two key challenges arise: (1) modeling the impact of hedgerows, trees, or panels on the microclimate; and (2) assessing how the modified microclimate influences vegetation energy and water balances.

To this end, the considered approach leverages the Computational Fluid Dynamics software code_saturne, which enables three-dimensional simulations of how obstacles alter the microclimate quantities. Vegetation effect on airflow is represented using source and sink terms following (Katul, et al., 2004, and Vernier, et al., 2026b), while the soil–plant–atmosphere continuum model developed by A. Tuzet is used to estimate plant energy and water balances, together with photosynthesis, and water stress (Tuzet, et al., 2003, and Vernier, et al., 2026a) (see Figure below). More recently, three-dimensional energy, water, and radiation balances at the leaf-agglomerate scale have been implemented into code_saturne to better simulate the influence of trees on the microclimate, and improve the accuracy and details of tree temperature estimations. 

The key drivers of plant temperature are simulated: incident radiation, convective exchange coefficient, stomatal conductance, together with air temperature and humidity. As illustrated in the Figure below, two heterogeneity scales are observed: a large one at the canopy level, and a small one at the tree level. On the one hand, trees attenuate wind speed by a factor of three between the inflow and the canopy flow, increasing convection resistance from approximately 15 s/m at the first trees with respect to the inflow to approximately 30 s/m for a tree at the center of the canopy. Alongside an approximate 1°C increase in air temperature, the first trees with respect to the inflow are about 2°C cooler than those located at the center of the canopy. On the other hand, part of each tree absorbs radiation while another one remains shaded, either by its own structure or by neighboring trees. This results in heterogeneous stomatal conductance at the tree scale, and, consequently, differences in plant temperature of more than 5°C. 

The next step consists in evaluating how combining trees, crops, hedgerows, and photovoltaic panels can help mitigate the impacts of heatwaves and droughts on agricultural production. Simulations of such systems are compared to measurements conducted at experimental agrivoltaic power plants, integrating photovoltaic panels above grapevines and apple trees, or obtained from agricultural fields located downstream of hedgerows. The ultimate goal is to optimize the geometry of panels, hedgerows, and trees to maximize their protective benefits, thereby boosting agricultural productivity and strengthening resilience to climate change.