Variability of vegetation fires with rain and deforestation in Brazil's state of Amazonas

- Biomass burning in Amazonia releases greenhouse gases.
- Climate change predictions indicate drying in Amazonia.
- Quantifying the relationship of fires to precipitation is needed.
- Hotspot data show fires occur more frequently under dryer conditions.

Understanding the variability of fire events and their relationship to precipitation and changes in land use and land cover is essential in order to evaluate the susceptibility of Amazonian vegetation. Time series of hotspots, of deforested area and of rainfall (all derived from satellite data) were used to determine the temporal and spatial distributions of fire in Brazil's state of Amazonas in order to establish the seasonal patterns of each variable and interactions with biomass burning. From 2003 to 2012, 60% of the hotspots detected were in the southern part of the state, with high variability between different months and years. Between 95% and 99% of the hotspots were recorded during the period of greatest occurrence of burning (July to March) with peaks during the months of August, September and October (the months with the lowest precipitation), suggesting that fires in Amazonas are mainly initiated by humans. Deforestation activity occurs approximately three months before the start of the burning activity. The number of hotspots did not show a relationship with the area deforested but showed a strong inverse relationship with rainfall. There is marked seasonal and annual variability, with patterns changing over time. Over the last decade the hotspots detected in Amazonas are associated not only with changes in land use and cover, but also with the use of fire in managing deforested areas.