Fires increase Amazon forest productivity through increases in diffuse radiation

Atmospheric aerosol scatters solar radiation increasing the fraction of diffuse radiation and the efficiency of photosynthesis. We quantify the impacts of biomass burning aerosol (BBA) on diffuse radiation and plant photosynthesis across Amazonia during 1998-2007. Evaluation against observed aerosol optical depth allows us to provide lower and upper BBA emissions estimates. BBA increases Amazon basin annual mean diffuse radiation by 3.4-6.8% and net primary production (NPP) by 1.4-2.8%, with quoted ranges driven by uncertainty in BBA emissions. The enhancement of Amazon basin NPP by 78-156TgCa-1 is equivalent to 33-65% of the annual regional carbon emissions from biomass burning. This NPP increase occurs during the dry season and acts to counteract some of the observed effect of drought on tropical production. We estimate that 30-60TgCa-1 of this NPP enhancement is within woody tissue, accounting for 8-16% of the observed carbon sink across mature Amazonian forests.This research was funded by the Natural Environment Research Council (NE/ J004723/1 and NE/J009822/1). P.A. was supported by FAPESP grants 2013/ 05014-0, 2014/50297-2 and CNPq. Data recorded in French Guiana benefited from an “Investissements d’Avenir” grant managed by Agence Nationale de la Recherche (CEBA ANR-10-LABX-25-01). We thank researchers from the TRENDY multimodel intercomparison project for access to data, the LBA central office at INPA for logistical support and the principal investigators and their staff for establishing and maintaining the AERONET sites used in this stud