Cloud–Forest Coupling: New insights integrating Amazon Observations and Explicit Canopy-Cloud Simulations

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 processes influence clear/cloud boundary layer dynamics 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 advance our understanding on the forest-cloud coupling, we focus on the Amazon basin as a proof-of-concept where we integrate field observations from the CloudRoots-Amazon22 campaign with new multi-layer canopy large-eddy simulations that explicitly resolve interactions between the forest canopy and the clear/cloudy boundary layer. The CloudRoots-Amazon22 experiment, conducted at the ATTO and Campina supersites during the August 2022 dry season, investigated the sub-diurnal evolution of the common clear-to-cloudy transition in the Amazon.

High-frequency observations reveal that stomatal conductance responds to variations in cloud optical thickness, demonstrating that canopy–cloud radiative perturbations regulate sub-diurnal canopy carbon and water exchange. Turbulent fluxes and vertical transport adjust within minutes to cloud passages, highlighting rapid land–atmosphere coupling. Collocated surface fluxes, profiles of thermodynamic variables, and CO₂ concentrations, further establish causal links between biophysical canopy processes and cloud dynamical development.

Building on these insights, we present an integrated framework that combines high-frequency observations with turbulence-resolving simulations embedded in global storm-resolving models to quantify shifts in cloud–forest coupling under climate change. This coupled approach advances our understanding of how cloud-radiative perturbations, turbulent transport, and photosynthesis co-evolve, bridging leaf-level processes and cloud-scale dynamics, and provides a pathway to constrain key uncertainties in Earth system models.