Impact of Future Warming and Enhanced [CO2] on the Vegetation-Cloud Interaction

The effects of increases in carbon dioxide and temperature on the vegetation-atmosphere-cloud interaction are studied with a bottom-up approach. Using the 3-D large-eddy simulation technique coupled with a CO2-sensitive dynamic plant physiological submodel, we aimed to spatially and temporally understand the surface and vegetation forcing on the coupled land-atmosphere interactions in future scenarios. Four simulations were designed: a control simulation for current conditions, an enhanced carbon dioxide simulation (current +200 ppm), an elevated temperature simulation (current +2 K), and a simulation covering the combination of both elevations in temperature and CO2. With elevations in carbon dioxide, plant transpiration is reduced due to stomatal closure, resulting in reduced latent- and increased sensible heat fluxes. Although no effects on cloud cover were found in this simulation, the in-cloud moisture flux was enhanced. Elevations in temperature yielded opposite results with reduced sensible and increased latent heat fluxes, which reduced the turbulent kinetic energy and buoyancy rates, thereby negatively impacting cloud formation. Our future climate mimicking simulation shows minimal changes in the regional energy balance due to offsetting effects between increased temperature and [CO2], while plant photosynthesis increased and transpiration decreased. The atmospheric boundary layer was drier, even though surface fluxes were very similar current conditions, thereby hampering cloud formation and development. Our results highlight the necessity of small scales and interactions, which require a bottom-up approach to be able to accurately capture the nonlinear plant-atmosphere interactions.