Abstract
AbstractFire risk in the Amazon can be predicted several months before the onset of the dry season using sea surface temperatures in the tropical north Atlantic and tropical Pacific. The lead times between ocean state and the period of maximum burning (4–11 months) may enable the development of forecasts with benefits for forest conservation, yet the underlying physical and biological mechanisms responsible for these temporal offsets are not well known. Here, we examined the hypothesis that year‐to‐year variations in soil water recharge during the wet season modify atmospheric water vapor and fire behavior during the following dry season. We tested this hypothesis by analyzing terrestrial water storage observations from the Gravity Recovery and Climate Experiment (GRACE), active fires from the Moderate Resolution Imaging Spectroradiometer (MODIS), and several other satellite and atmospheric reanalysis datasets during 2002–2011. We found that terrestrial water storage deficits preceded severe fire seasons across the southern Amazon. The most significant relationships between monthly terrestrial water storage and the sum of active fires during the dry season occurred during April–August (p < 0.02), corresponding to 1–5 month lead times 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 terrestrial water storage, and subsequently, surface and column atmospheric water vapor. Our results suggest that terrestrial water storage observations from GRACE have the potential to improve fire season forecasts for the southern Amazon.
Highlights
[7] Based on this set of mechanisms, fire season severity in the Amazon may be sensitive to water storage anomalies that occur near the beginning of the dry season in response to the cumulative effect of precipitation and evapotranspiration anomalies in preceding months
[13] For each region described in Figure 1, we examined the correlations between terrestrial water storage sampled during different months before the fire season and the fire season severity
The cumulative effect of below average precipitation and above average evapotranspiration in high fire years (Figures 6a and 6b) appeared to drive the observed deficits in terrestrial water storage that were significant at the end of the wet season and through the middle of the dry season
Summary
[2] Fires in the Amazon modify many important linkages in the Earth system and are a major threat to efforts to manage these ecosystems sustainably. [7] Based on this set of mechanisms, fire season severity in the Amazon may be sensitive to water storage anomalies that occur near the beginning of the dry season in response to the cumulative effect of precipitation and evapotranspiration anomalies in preceding months We tested this hypothesis using satellite observations of terrestrial water storage from the Gravity Recovery and Climate Experiment (GRACE) and active fires from the Moderate Resolution Imaging Spectroradiometer (MODIS) [Giglio et al, 2003]. We examined three regions in the southern Amazon (Figure 1), which encompass most of the active fire observations in evergreen broadleaf forests in the basin (approximately 75%) We chose these three large overlapping 750 km radius discs for our analysis because we wanted to resolve important east-west differences in drought and fire noted in earlier studies [Chen et al, 2011], yet retain large enough footprints with GRACE to maintain high signal-to-noise ratios for the monthly terrestrial water storage retrievals. With the use of these multiple satellite observations, we developed a conceptual model of the physical and biological mechanisms contributing to the SST-fire teleconnections described in earlier work
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