Abstract
AbstractGlobal carbon emissions from fires are difficult to quantify and have the potential to influence interannual variability and long‐term trends in atmospheric CO2 concentrations. We used 4 years of Tropical Rainfall Measuring Mission (TRMM) Visible and Infrared Scanner (VIRS) satellite data and a biogeochemical model to assess spatial and temporal variability of carbon emissions from tropical fires. The TRMM satellite data extended between 38°N and 38°S and covered the period from 1998 to 2001. A relationship between TRMM fire counts and burned area was derived using estimates of burned area from other satellite fire products in Africa and Australia and reported burned areas from the United States. We modified the Carnegie‐Ames‐Stanford‐Approach (CASA) biogeochemical model to account for both direct combustion losses and the decomposition from fire‐induced mortality, using both TRMM and Sea‐viewing Wide Field of view Sensor (SeaWiFS) satellite data as model drivers. Over the 1998–2001 period, we estimated that the sum of carbon emissions from tropical fires and fuel wood use was 2.6 Pg C yr−1. An additional flux of 1.2 Pg C yr−1 was released indirectly, as a result of decomposition of vegetation killed by fire but not combusted. The sum of direct and indirect carbon losses from fires represented 9% of tropical and subtropical net primary production (NPP). We found that including fire processes in the tropics substantially alters the seasonal cycle of net biome production by shifting carbon losses to months with low soil moisture and low rates of soil microbial respiration. Consequently, accounting for fires increases growing season net flux by ∼12% between 38°N and 38°S, with the greatest effect occurring in highly productive savanna regions.
Highlights
Biomass burning and wildfires play an important role in the cycling of carbon in many ecosystems and represent a significant source of aerosols and trace gas emissions, in tropical and boreal regions (Crutzen & Andreae, 1990; Hao et al, 1990; Kasischke et al, 1995)
When scaling our burned area for southern Africa to the values reported in two other studies (Scholes et al, 1996; Barbosa et al, 1999b) and extrapolating that relationship to the Tropical Rainfall Measuring Mission (TRMM) domain we found an increase in emissions of 38% with an increase of area burned of 55%
We estimated that for the region observed by the TRMM satellite (388N to 388S), 2.6 Pg C yrÀ1 was lost as direct emissions and an extra 1.2 Pg C yrÀ1 was lost as respiration from fire-induced mortality
Summary
Biomass burning and wildfires play an important role in the cycling of carbon in many ecosystems and represent a significant source of aerosols and trace gas emissions, in tropical and boreal regions (Crutzen & Andreae, 1990; Hao et al, 1990; Kasischke et al, 1995). Studies estimated carbon losses from fires on a continental or global scale by developing inventories of aggregated fuel, combustion factors, and fire return times for different biome types, and extrapolating regional emissions estimates using global vegetation maps. Using an indirect satellite method, Scholes et al (1996) showed that the inventorybased methods overestimated burned areas when FRTs from productive savanna and other ecosystems that burn frequently were assumed to represent larger regions. Using a direct satellite-based measurement of fire scars, Barbosa et al (1999a) obtained burned areas for southern Africa that had considerable interannual variability, but with a mean comparable to the earlier estimates from Scholes et al (1996). During the 1980s in Africa, they found that emissions in a high fire year were double those in a low fire year
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