Abstract
Abstract. Significant inter-annual variability of biomass burning was observed in South America over the 2007–2009 period. The 2007 number of fires detected from space in South America, as well as the magnitude of the atmospheric aerosol load resulting from fire activity, was the largest over the last ten years. The huge 2007 increase in fire activity was followed by large reductions in the 2008 and 2009 burning seasons. Large drops of the atmospheric load of carbonaceous aerosols over the subcontinent, relative to previous years, was registered in 2008 and 2009 by the OMI sensor onboard the Aura platform, and the MODIS sensors on the Terra and Aqua satellites. The 2009 fire season in South America was the least active of the last ten years. Satellite observations of fire statistics, precipitation, and aerosol optical depth data were used to analyze the fire season over South America and Central Africa during the last ten years to understand the factors that led to the 2007 and 2009 extremes. An analysis of precipitation anomaly data shows that the largest 6-month (May–October) precipitation deficit of the last ten years in South America occurred during 2007. The same analysis indicates that in 2009, this region experienced the largest excess precipitation of the decade. Since precipitation is the most important meteorological factor controlling biomass burning activity, it can be concluded that the 2007 maximum and 2009 minimum in fire activity and aerosol load were driven by the observed levels of precipitation. Analysis of the precipitation record, however, does not explain the extremely low 2008 biomass burning activity. Although the 2008 precipitation deficit was similar in magnitude to the one that in 2005 contributed to the second most intense biomass burning season in the last ten years, the 2008 fire season was surprisingly weak. The combined analysis of satellite data on atmospheric aerosol load, fire counts and precipitation strongly suggests that the observed 2008 decline in aerosol load and fire activity in South America was heavily influenced by conditions other than meteorological factors.
Highlights
Biomass burning is a widespread agricultural practice for land clearing used in most tropical farmlands in South America (SA) and Central and Southern Africa (CA)
The 2007–2008 fire reduction following political boundaries suggests that the 2008 decrease in burning observed in South America might have been related to the effect of economic and/or regulatory forces that were in effect primarily in Brazil resulting in a lesser number of fires ignited
The observed decrease in the OMI signal and MODIS extinction optical depth in 2008 and 2009 over South America is consistent with the reported fire count statistics that clearly indicate an actual reduction in the number of fires in South America during the burning seasons in 2008 and 2009
Summary
Biomass burning is a widespread agricultural practice for land clearing used in most tropical farmlands in South America (SA) and Central and Southern Africa (CA). Koren et al (2007, 2009) examined the inter-annual variability of biomass burning in the Amazon basin using MODIS aerosol optical depth data and fire counts observations from the NOAA-12 Advanced Very High Resolution Radiometer (AVHRR) in the period 2000– 2006. They reported a generally increasing trend up to about 2005 followed by a sudden drop in 2006. The effect of the reduced 2008 fire activity in South America on tropospheric ozone production is analyzed by Ziemke et al, (2009)
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