Implementation of MEGAN v3.2 in SURFEX v9.0: A new framework for global biogenic emission simulations

Abstract. Biogenic volatile organic compounds (BVOCs), and isoprene in particular, strongly influence tropospheric chemistry, air quality, and climate feedbacks, making their accurate representation essential in atmospheric chemistry and climate modelling. However, simulated global isoprene budgets remain highly uncertain, spanning a wide range across models due to differences in emission factor datasets, land-surface descriptions, and environmental stress parametrizations. A recent study implemented the MEGAN v2.1 biogenic emission model within the SURFEX land-surface model, but this framework did not include developments introduced in MEGAN v3.2 or updates to SURFEX itself. Here we present the implementation and evaluation of MEGAN v3.2 within SURFEX v9.0 and compare it with the former MEGAN v2.1 – SURFEX v8.1 configuration. Global offline simulations for 2019 were performed using two meteorological forcing datasets to assess the sensitivity of simulated isoprene emissions to the MEGAN upgrade, soil moisture stress, emission factor parametrization, and land-cover description. Specifically, the transition from MEGAN v2.1 to v3.2 strongly reduces global annual isoprene emissions, yielding totals of 216–318 Tg yr⁻¹, primarily driven by the updated gridded emission factor dataset prescribing lower emission potentials across most land regions. These lower totals are nonetheless consistent with recent evidence suggesting that MEGAN v2.1 overestimates emission potentials for certain vegetation types, and the spatial distribution and seasonal variability of isoprene remain largely preserved, indicating that the upgrade mainly rescales emission magnitudes rather than reorganizing global emission patterns. Sensitivity experiments further demonstrate that emission factor parametrization and land-cover description constitute first-order controls on simulated isoprene budgets, with associated uncertainties exceeding those related to meteorological forcing. The upgraded SURFEX-MEGAN framework therefore provides a robust basis for future coupled atmospheric chemistry applications.