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Discussion papers
https://doi.org/10.5194/acp-2018-924
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2018-924
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 18 Sep 2018

Research article | 18 Sep 2018

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Studying the impact of biomass burning aerosol radiative and climate effects on the Amazon rainforest productivity with an Earth System Model

Florent F. Malavelle1, Jim M. Haywood1,2, Lina M. Mercado3,4, Gerd A. Folberth2, Nicolas Bellouin5, Stephen Sitch3, and Paulo Artaxo6 Florent F. Malavelle et al.
  • 1CEMPS, University of Exeter, Exeter, EX4 4QE, UK
  • 2UK Met-Office Hadley Centre, Exeter, EX1 3PB, UK
  • 3CLES, University of Exeter, Exeter, EX4 4RJ, UK
  • 4Centre for Ecology and Hydrology, OX10 8BB, UK
  • 5Department of Meteorology, University of Reading, Reading, RG6 6BB, UK
  • 6Department of Applied Physics, Institute of Physics, University of Sao Paulo, Sao Paulo, Brazil

Abstract. Diffuse light conditions can increase the efficiency of photosynthesis and carbon uptake by vegetation canopies. The diffuse fraction of photosynthetically active radiation (PAR) can be affected by either a change in the atmospheric aerosol burden and/or a change in cloudiness. During the dry season, a hotspot of Biomass Burning on the edges of the Amazon rainforest emits a complex mixture of aerosols and their precursors and climate-active trace gases (e.g. CO2, CH4, NOx etc). This creates potential for significant interactions between chemistry, aerosol, cloud, radiation and the biosphere across the Amazon region. The combined effects of biomass burning on the terrestrial carbon cycle for the present-day are potentially large, yet poorly quantified. Here, we quantify such effects using the Met Office Hadley Centre Earth System Model HadGEM2-ES which provides a fully coupled framework with interactive aerosol, radiative transfer, dynamic vegetation, atmospheric chemistry and biogenic volatile organic compound emission components. Results show that the overall net impact of present-day biomass burning aerosols is to increase net primary productivity (NPP) by +80 to +105TgC/yr, or 1.9 to 2.7%, over the central Amazon basin on annual mean. For the first time we show that this enhancement is the net result of multiple competing effects: an increase in diffuse light which stimulates photosynthetic activity in the shaded part of the canopy (+65 to +110TgC/yr), a reduction in the total amount of radiation (−52 to −105TgC/yr) which reduces photosynthesis and feedback from climate adjustments in response to the aerosol forcing which increases the efficiency of biochemical processes (+67 to +100TgC/yr). These results illustrate that despite a modest direct aerosol effect (the sum of the first two counteracting mechanisms) the overall, net impact of biomass burning aerosols on vegetation, is sizeable, when indirect climate feedbacks are considered. We demonstrate that capturing the net impact of aerosols on vegetation should be assessed considering the system-wide behaviour.

Florent F. Malavelle et al.
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Florent F. Malavelle et al.
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Diffuse light can increase the efficiency vegetation photosynthesis. Diffuse light results from scattering by either clouds or aerosols in the atmosphere. During the dry season biomass burning on the edges of the Amazon rainforest contributes significantly to the aerosol burden over the entire region. We show that despite a modest effect of change in light condition, the overall impact of biomass burning aerosols on the vegetation is yet important when indirect climate feedbacks are considered.
Diffuse light can increase the efficiency vegetation photosynthesis. Diffuse light results from...
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