Towards a more detailed representation of high-latitude vegetation in the global land surface model ORCHIDEE (ORC-HL-VEGv1.0)

Arsène Druel, Philippe Peylin, Gerhard Krinner, Philippe Ciais, Nicolas Viovy, Anna Peregon, Vladislav Bastrikov, Natalya Kosykh, Nina Mironycheva-Tokareva
2017 Geoscientific Model Development  
<p><strong>Abstract.</strong> Simulation of vegetation–climate feedbacks in high latitudes in the ORCHIDEE land surface model was improved by the addition of three new circumpolar plant functional types (PFTs), namely non-vascular plants representing bryophytes and lichens, Arctic shrubs and Arctic C<sub>3</sub> grasses. Non-vascular plants are assigned no stomatal conductance, very shallow roots, and can desiccate during dry episodes and become active again during wet periods, which gives them
more » ... a larger phenological plasticity (i.e. adaptability and resilience to severe climatic constraints) compared to grasses and shrubs. Shrubs have a specific carbon allocation scheme, and differ from trees by their larger survival rates in winter, due to protection by snow. Arctic C<sub>3</sub> grasses have the same equations as in the original ORCHIDEE version, but different parameter values, optimised from in situ observations of biomass and net primary productivity (NPP) in Siberia. In situ observations of living biomass and productivity from Siberia were used to calibrate the parameters of the new PFTs using a Bayesian optimisation procedure. With the new PFTs, we obtain a lower NPP by 31<span class="thinspace"></span>% (from 55°<span class="thinspace"></span>N), as well as a lower roughness length (−41<span class="thinspace"></span>%), transpiration (−33<span class="thinspace"></span>%) and a higher winter albedo (by +3.6<span class="thinspace"></span>%) due to increased snow cover. A simulation of the water balance and runoff and drainage in the high northern latitudes using the new PFTs results in an increase of fresh water discharge in the Arctic ocean by 11<span class="thinspace"></span>% (+140<span class="thinspace"></span>km<sup>3</sup><span class="thinspace"></span>yr<sup>−1</sup>), owing to less evapotranspiration. Future developments should focus on the competition between these three PFTs and boreal tree PFTs, in order to simulate their area changes in response to climate change, and the effect of carbon–nitrogen interactions.</p>
doi:10.5194/gmd-10-4693-2017 fatcat:zhtwkuicd5ccbpcclwip6fp3fa