Incorporating vegetation dynamics for terrestrial isoprene and monoterpene emission estimates: Linking LPJ-GUESS (v4.0) with the EMAC modelling system (v2.54)

Earth system models (ESMs) are state-of-the-art models which integrate previously separate models of the ocean, atmosphere and vegetation in one comprehensive modelling system enabling the investigation of interactive feedbacks between different components of the Earth system. Global isoprene and monoterpene emissions from terrestrial vegetation, which represents the most important source of VOCs in the Earth system, are needed for a suitable representation in global and regional chemical transport models given their impacts on the atmosphere. Consequently, to accurately determine the budget of isoprene and monoterpenes in the atmosphere, adequate emissions from the terrestrial vegetation are a requirement for input into regional and global scale chemistry-transport or chemistry-climate models. Due to the feedbacks of vegetation activity involving interactions with the weather and climate, a coupled modelling system between vegetation and atmospheric chemistry is a recommended tool to address the fate of biogenic volatile organic compounds (bVOCs). In this work, we present further development in linking LPJ-GUESS, a global dynamic vegetation model, to the atmospheric chemistry-enabled atmosphere-ocean general circulation model EMAC. We evaluate terrestrial bVOC emission estimates from the submodel ONEMIS in EMAC with (1) prescribed climatological vegetation boundary conditions at the land-atmosphere interface; and (2) dynamic vegetation states calculated in LPJ-GUESS (replacing the “offline” vegetation inputs). LPJ-GUESS-driven global emission estimates for isoprene and monoterpenes were found to be 599 Tg yr⁻¹ and 111 Tg yr⁻¹, respectively. Additionally, we evaluated the sensitivity of the new coupled system in doubling CO₂ scenarios. Higher temperatures resulted in an increase in bVOC emissions (+47% and +69% for isoprene and monoterpenes, respectively), whereas CO₂-fertilisation resulted in an increase of 18% in isoprene emissions and 37% in monoterpene emissions. We provide evidence that the new coupled model yields suitable estimates for global bVOC emissions that are responsive to vegetation dynamics, thus enabling further research in land-biosphere-atmosphere interactions.