Abstract
Fires are a fundamental part of the Earth System. In the last decades, they have been altering ecosystem structure, biogeochemical cycles and atmospheric composition with unprecedented rapidity. In this study, we implement a complex networks-based methodology to track individual fires over space and time. We focus on extreme fires—the 5% most intense fires—in the tropical forests of the Brazilian Legal Amazon over the period 2002–2019. We analyse the interannual variability in the number and spatial patterns of extreme forest fires in years with diverse climatic conditions and anthropogenic pressure to examine potential synergies between climate and anthropogenic drivers. We observe that major droughts, that increase forest flammability, co-occur with high extreme fire years but also that it is fundamental to consider anthropogenic activities to understand the distribution of extreme fires. Deforestation fires, fires escaping from managed lands, and other types of forest degradation and fragmentation provide the ignition sources for fires to ignite in the forests. We find that all extreme forest fires identified are located within a 0.5-km distance from forest edges, and up to 56% of them are within a 1-km distance from roads (which increases to 73% within 5 km), showing a strong correlation that defines spatial patterns of extreme fires.
Highlights
Between deforestation and fire because the decrease in fire activity was not as strong as the decline in deforestation during the period 2003–2015
We find a total of 351.991 fire clusters in tropical evergreen forests of the Brazilian Legal Amazon (BLA) over the period 2002–2019, which account for 43% of the total number of fire clusters registered in the 18-year period in the region
Our findings are in line with previous studies underscoring that both climatic and anthropogenic factors determine the spatiotemporal distribution of extreme fires in the region
Summary
Warm Sea Surface Temperature (SST) in the tropical North Atlantic weakens northeast trade wind moisture transport during the summer resulting in reduced rainfall during the dry season especially in western and southwestern Amazon [15,16]. We apply the complex networks-based methodology developed in Traxl et al [35,36] to fire data for the first time We implement this novel methodology to identify individual fires and track their evolution over space and time. We compare spatial occurrence and interannual variability of extreme fires in evergreen forests of the BLA and interpret both spatial and temporal patterns in relation to large-scale climate events, and to anthropogenic drivers such as deforestation and road development. We address the following objectives: (1) apply a novel network-based methodological approach that enables us to identify individual fires for the evaluation of spatio-temporal dynamics of extreme fires in Amazonian evergreen forests. (3) Identify potential impacts of climatic drivers such as the ENSO- and AMO-associated severe droughts, as well as anthropogenic drivers such as deforestation and distance from roads and forest edges on the spatiotemporal variability of extreme fires
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