Colloquium: Jordi Vila-Guerau de Arellano

Forests and clouds are central to Earth’s carbon and water cycles, yet they are rarely studied as a coupled system. Recent observations reveal concurrent shifts in forest CO₂ uptake and cloud regimes across tropical, temperate, and boreal biomes, signaling changes in forest–atmosphere coupling with profound implications for cloud cycling and climate feedbacks. While rising CO₂ may enhance forest assimilation, declining trends in low cloud cover alters radiative fluxes and amplifies warming, potentially modifying forest photosynthesis, turbulence, and biogenic volatile organic compound emissions. In turn, these forest processes by controlling the partitioning of canopy turbulent fluxes, influence boundary-layer dynamics and cloud formation, yet current Earth system models largely overlook these cross-scale interactions.

To address this gap, and focusing on the Amazonia basin, we combine field observations from CloudRoots-Amazon22 field campaign, including remote sensing, with new multi-layer large-eddy simulations and high-resolution global models. CloudRoots-Amazon22 experiment, conducted at the ATTO/Campina supersites during August 2022 dry season, investigated the diurnal evolution of the clear-to-cloudy transition in the Amazon. High-frequency observations revealed that stomatal conductance responds to cloud optical thickness, that canopy–cloud radiative perturbations regulate sub-diurnal carbon and water exchange, and that turbulent fluxes and vertical transport adjust within minutes to cloud passages. Collocated surface fluxes, profiles of state variables, and carbon dioxide further established causal relationships between biophysical canopy processes and cloud mass fluxes.Building on these insights, I will present how we currently integrate high-frequency observations with turbulence-resolving simulations embedded in global storm-resolving models to quantify emergent shifts in cloud–forest coupling under changing climates. This integrated framework advances our understanding of how convective organization and photosynthesis co-evolve—bridging the gap between leaf-level processes and cloud-scale dynamics—essential to improve climate predictions.