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Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
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Volume 11, issue 7
Geosci. Model Dev., 11, 2857-2873, 2018
https://doi.org/10.5194/gmd-11-2857-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Geosci. Model Dev., 11, 2857-2873, 2018
https://doi.org/10.5194/gmd-11-2857-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Development and technical paper 13 Jul 2018

Development and technical paper | 13 Jul 2018

Vegetation distribution and terrestrial carbon cycle in a carbon cycle configuration of JULES4.6 with new plant functional types

Anna B. Harper1, Andrew J. Wiltshire2, Peter M. Cox1, Pierre Friedlingstein1, Chris D. Jones2, Lina M. Mercado3,4, Stephen Sitch3, Karina Williams2, and Carolina Duran-Rojas1 Anna B. Harper et al.
  • 1College of Engineering, Mathematics, and Physical Sciences, University of Exeter, Exeter EX4 4QF, UK
  • 2Met Office Hadley Centre, Fitzroy Road, Exeter EX1 3PB, UK
  • 3College of Life and Environmental Sciences, University of Exeter, Exeter EX4 4PS, UK
  • 4Centre for Ecology and Hydrology, Wallingford OX10 8BB, UK

Abstract. Dynamic global vegetation models (DGVMs) are used for studying historical and future changes to vegetation and the terrestrial carbon cycle. JULES (the Joint UK Land Environment Simulator) represents the land surface in the Hadley Centre climate models and in the UK Earth System Model. Recently the number of plant functional types (PFTs) in JULES was expanded from five to nine to better represent functional diversity in global ecosystems. Here we introduce a more mechanistic representation of vegetation dynamics in TRIFFID, the dynamic vegetation component of JULES, which allows for any number of PFTs to compete based solely on their height; therefore, the previous hardwired dominance hierarchy is removed.

With the new set of nine PFTs, JULES is able to more accurately reproduce global vegetation distribution compared to the former five PFT version. Improvements include the coverage of trees within tropical and boreal forests and a reduction in shrubs, the latter of which dominated at high latitudes. We show that JULES is able to realistically represent several aspects of the global carbon (C) cycle. The simulated gross primary productivity (GPP) is within the range of observations, but simulated net primary productivity (NPP) is slightly too high. GPP in JULES from 1982 to 2011 is 133PgCyr−1, compared to observation-based estimates (over the same time period) between 123±8 and 150–175PgCyr−1. NPP from 2000 to 2013 is 72PgCyr−1, compared to satellite-derived NPP of 55PgCyr−1 over the same period and independent estimates of 56.2±14.3PgCyr−1. The simulated carbon stored in vegetation is 542PgC, compared to an observation-based range of 400–600PgC. Soil carbon is much lower (1422PgC) than estimates from measurements ( > 2400PgC), with large underestimations of soil carbon in the tropical and boreal forests.

We also examined some aspects of the historical terrestrial carbon sink as simulated by JULES. Between the 1900s and 2000s, increased atmospheric carbon dioxide levels enhanced vegetation productivity and litter inputs into the soils, while land use change removed vegetation and reduced soil carbon. The result is a simulated increase in soil carbon of 57PgC but a decrease in vegetation carbon of 98PgC. The total simulated loss of soil and vegetation carbon due to land use change is 138PgC from 1900 to 2009, compared to a recent observationally constrained estimate of 155±50PgC from 1901 to 2012. The simulated land carbon sink is 2.0±1.0PgCyr−1 from 2000 to 2009, in close agreement with estimates from the IPCC and Global Carbon Project.

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Dynamic global vegetation models are used for studying historical and future changes to vegetation and the terrestrial carbon cycle. JULES is a DGVM that represents the land surface in the UK Earth System Model. We compared simulated gross and net primary productivity of vegetation, vegetation distribution, and aspects of the transient carbon cycle to observational datasets. JULES was able to accurately reproduce many aspects of the terrestrial carbon cycle with the recent improvements.
Dynamic global vegetation models are used for studying historical and future changes to...
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