Forest microclimate representations in land surface and ecosystem models: an inter-comparison

Land Surface Models (LSMs) are key components of Earth system models as they describe the spatial and temporal dynamics of vegetation and how it exchanges energy, momentum, water and CO2 with the atmosphere. These models have been greatly improved over the last fifty years to include more and more processes such as carbon and nutrient cycling, plant hydraulics or vegetation dynamics. However, in most LSMs, the vertical structure of vegetation canopies is taken into account only implicitly, through surface parameters such as displacement height or roughness height. This implicit representation of vegetation canopies prevents the estimation of the microclimate within and below the canopy and its influence on the energy, water and carbon exchanges. The representation of below-canopy microclimate seems to be a key development in order to improve energy and water balance descriptions in LSMs and our knowledge on forest response to a changing climate. This need justifies the current efforts of the land surface community to explicitly represent canopy microclimate in LSMs. This poster presents the main developments introduced in the ORCHIDEE LSM to address this need. A multi-layer energy budget representation previously implemented in an earlier version of ORCHIDEE (Ryder et al. (2015)) has been re-implemented, adapted and improved in the main ORCHIDEE version (i.e. Trunk) in order to represent the exchange of water and energy between vegetation and the atmosphere, and the turbulent transport of mass, energy and momentum within vegetation canopies. This model is evaluated against in situ observations, and compared with a more complex ecosystem model, MuSICA (Ogée et al. (2003)). To provide a comprehensive understanding of the strengths and drawbacks of the two models, and to pave the way to future improvements to the ORCHIDEE LSM, this model inter-comparison is carried out over a dataset that gathers measurements of intra-canopy temperature and humidity profiles and fluxes from 10 forest sites. In addition to the results of this inter-comparison, new perspectives for the ORCHIDEE community and general thoughts on microclimate modelling in LSMs induced by these developments will be drawn.