Incêndios florestais e queimadas no Amazonas: distribuição, suscetibilidade e emissões de carbono

Abstract

In Amazonia, fire is one of the most important disturbance agents through its connection with the land-use activities, atmospheric composition and the global carbon cycle. The results presented in the present study provide substantial information about the patterns and behavior of fire and its interactions with land use and meteorological components, as well as the impacts of forest fires on biomass and carbon emissions in Brazil‟s state of Amazonas. In Chapter 1 time series are derived from satellite data for hotspots, deforestation and rain, and these are used to determine the temporal and spatial distributions of fire in Amazonas. The seasonal patterns of each variable are determined together with their interactions with biomass burning. Of hotspots detected in the state of Amazonas, 60% were in the southern part of the state (with great temporal variability on both monthly and yearly timescales). Between 95% and 99% of the hotspots were recorded during the burning highest activity period (July to March) with peaks in frequency between August and October (the period of the year with the lowest precipitation). Deforestation activity occurs approximately three months before the start of the burning activity. The number of hotspots showed no linear relationship with the area deforested (p = 0.294, r² = 0.002, n = 68, DETER data; p = 0.357, r² = 0.000, n = 10, PRODES data), but strong inverse relationship with precipitation (p < 0.001, b = -0.009, n = 120). Hotspots are clustered in areas undergoing deforestation. There is marked seasonal and annual variability, with patterns changing over time. In Chapter 2 we determined the meteorological conditions under which the largest number of fire events occurs in southern Amazonas in a dry year (2004) and in a year (2005) with a severe drought that was provoked by a climate anomaly. In the year with the severe drought the spatial extent of the area in the southern part of the state of Amazonas that was susceptible to fire was 83% greater than in. In 2004 and 2005, 48% and 79%, respectively, of the cells with hotspots had weather conditions that were conducive to combustion, with monthly rainfall below 100 mm, average air temperature greater than 24°C, and relative humidity less than 65% (mainly in August and September). The number of hotspots detected in 2005 was more than twice the number detected in 2004. Meteorological parameters showed a tendency to differ between years, but not between areas with and without hotspots (PC1 = 48%, PC2 = 22%). Meteorological parameters showed values quite predictors of fire occurrence in the state of Amazonas (b = 0,83; p < 0,001; EP = 0,13; n = 8). Chapter 3 presents estimates areas affected by forest fires that occurred in 2005 in the municipalities of Boca do Acre and Lábrea (in the southern portion of the state of Amazonas) and presents estimates of loss of biomass and carbon stocks, as well as estimates of committed emissions from increased mortality of trees as a result of the fire. Fire scars observed on Landsat TM-5 satellite images from 2004-2006 were interpreted visually and were digitalized. We mapped ~865,6 km² of forest affected by fire, most (2.9% of the total forest cover) was concentrated along the southern borders of the municipalities bordering the states of Rondônia and Acre. The greatest loss of biomass due to an increase mortality of trees occurred four years after the fire: 4.5 × 106 Mg (total) and 3.7 × 106 Mg (above ground). Consequently, 2.2 × 106 Mg C (total) and 1.8 × 106 Mg C (above ground) of potential carbon emissions were committed from the initial burning of forest biomass and from the trees killed by the fire. Emissions occur through oxidation of dead biomass either by decomposition or by combustion. Forest fires affect extensive areas of forest and can emit significant quantities of carbon into the atmosphere in periods of severe drought.