Abstract

Tropical carbon emissions are largely derived from direct forest clearing processes. Yet, emissions from drought-induced forest fires are, usually, not included in national-level carbon emission inventories. Here we examine Brazilian Amazon drought impacts on fire incidence and associated forest fire carbon emissions over the period 2003–2015. We show that despite a 76% decline in deforestation rates over the past 13 years, fire incidence increased by 36% during the 2015 drought compared to the preceding 12 years. The 2015 drought had the largest ever ratio of active fire counts to deforestation, with active fires occurring over an area of 799,293 km2. Gross emissions from forest fires (989 ± 504 Tg CO2 year−1) alone are more than half as great as those from old-growth forest deforestation during drought years. We conclude that carbon emission inventories intended for accounting and developing policies need to take account of substantial forest fire emissions not associated to the deforestation process.

Highlights

  • Tropical carbon emissions are largely derived from direct forest clearing processes

  • Our analysis of sea surface temperature anomalies (SSTA) showed that the two strongest droughts in this century, occurring in 2005 and 2010, were strongly correlated with the anomalous warming of the Atlantic ocean captured by the Atlantic Multidecadal Oscillation (AMO)[19, 20] index (Fig. 1a–e)

  • The 2015 drought occurred following a simultaneous development of anomalous warming of the equatorial and eastern tropical north Pacific and tropical north Atlantic oceans, as measured by the Multivariate El Nino Index (MEI)[21], the Pacific Decadal Oscillation (PDO)[22] and the AMO19, 20 indices, respectively (Figs 1a–e and 2a)

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Summary

Introduction

Tropical carbon emissions are largely derived from direct forest clearing processes. Yet, emissions from drought-induced forest fires are, usually, not included in national-level carbon emission inventories. Most Earth System Models (ESMs) predict increasing dry season intensity in Amazonia in the 21st century This is directly related to radiative forcing[11] and declining Northern Hemisphere aerosol production[12, 13], which tend to cause anomalous variation of sea surface temperatures (SST) and drive large-scale swings in precipitation over Amazonia. Recent drought events (i.e., 2005, 2010 and 2015) can serve as a model for assessing how oceanic modes shift the amount and distribution of Amazonian rainfall, in turn affecting spatio-temporal patterns of fire-prone regions in future climate conditions These events, provide a unique opportunity to quantify the sensitivity of drought-fire interaction under the current trend of reduced deforestation rates in the Brazilian Amazon. We analyze 13 years of monthly time series (2003–2015) of sea surface temperature anomalies (SSTA) indices[19,20,21,22] combined with a suite of satellite-derived rainfall[23], active fire detections[24], atmospheric carbon monoxide (CO)[25], annual deforestation[7] and burned area data for the Brazilian Amazon

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