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European Geosciences Union, Geoscientific Model Development, 2(8), p. 431-452, 2015

DOI: 10.5194/gmd-8-431-2015

Copernicus Publications, Geoscientific Model Development Discussions, 5(7), p. 6845-6891

DOI: 10.5194/gmdd-7-6845-2014

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A test of an optimal stomatal conductance scheme within the CABLE land surface model

Journal article published in 2014 by Mg G. De Kauwe ORCID, Jatin Kala, Ys-S. Lin ORCID, Aj J. Pitman, Be E. Medlyn ORCID, Ra A. Duursma, Gab Abramowitz ORCID, Yp-P. Wang ORCID, Diego G. Miralles ORCID
This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Abstract

Abstract. Stomatal conductance (gs) affects the fluxes of carbon, energy and water between the vegetated land surface and the atmosphere. We test an implementation of an optimal stomatal conductance model within the Community Atmosphere Biosphere Land Exchange (CABLE) land surface model (LSM). In common with many LSMs, CABLE does not differentiate between gs model parameters in relation to plant functional type (PFT), but instead only in relation to photosynthetic pathway. We constrained the key model parameter "g1", which represents plant water use strategy, by PFT, based on a global synthesis of stomatal behaviour. As proof of concept, we also demonstrate that the g1 parameter can be estimated using two long-term average (1960–1990) bioclimatic variables: (i) temperature and (ii) an indirect estimate of annual plant water availability. The new stomatal model, in conjunction with PFT parameterisations, resulted in a large reduction in annual fluxes of transpiration (~ 30% compared to the standard CABLE simulations) across evergreen needleleaf, tundra and C4 grass regions. Differences in other regions of the globe were typically small. Model performance against upscaled data products was not degraded, but did not noticeably reduce existing model–data biases. We identified assumptions relating to the coupling of the vegetation to the atmosphere and the parameterisation of the minimum stomatal conductance as areas requiring further investigation in both CABLE and potentially other LSMs. We conclude that optimisation theory can yield a simple and tractable approach to predicting stomatal conductance in LSMs.