Sea surface temperatures and terrestrial water storage provide early warning information about fire season severity in the Amazon

Fires in South America cause forest degradation and contribute to carbon emissions associated with land use change. We investigated the relationship between year-to-year changes in satellite observations of active fires in South America and sea surface temperatures. We found that the Oceanic Niño Index was correlated with interannual fire activity in the eastern Amazon whereas the Atlantic Multidecadal Oscillation index was more closely linked with fires in the southern and southwestern Amazon. Combining these two climate indices, we developed an empirical model that predicted regional fire season severity with 3-5 month lead times. We further examined the hypothesis that year-to-year variations in soil water recharge during the wet season modifies atmospheric water vapor and fire behavior during the following dry season. We tested this hypothesis by analyzing terrestrial water storage (TWS) observations from the Gravity Recovery and Climate Experiment (GRACE), active fires from the Moderate Resolution Imaging Spectroradiometer (MODIS), and other satellite and climate data during 2002-2011. We found that TWS anomalies at the end of the wet season were negatively correlated with the number of active fires during the dry season for three regions across the southern Amazon. The most significant relationships (p < 0.02) were observed for TWS anomalies during April-August, several months before the peak month of burning (September). Analysis of other datasets provided evidence for a cascade of processes during drought events, with lower cumulative precipitation (and higher cumulative evapotranspiration) in the wet season substantially reducing TWS, and subsequently surface and column water vapor. Our results indicate that TWS from GRACE also has the potential to provide early warning information about fire season severity in the Amazon.