Authors:

David L. A. Gaveau¹, Mohammad A. Salim¹, Kristell Hergoualc’h¹, Bruno Locatelli^1,2, Sean Sloan³,
Martin Wooster⁴, Miriam E. Marlier⁵, Elis Molidena¹, Husna Yaen¹, Ruth DeFries⁵, Louis Verchot^1,6,
Daniel Murdiyarso^1,7, Robert Nasi¹, Peter Holmgren¹ & Douglas Sheil^1,8

¹Center for International Forestry Research, P.O. Box 0113 BOCBD, Bogor 16000, Indonesia,
²UPR BSEF, CIRAD, TA C-105/D, Campus international de Baillarguet, 34398 Montpellier Cedex 5, France,
³Centre for Tropical Environmental and Sustainability Science, School of Marine & Tropical Biology, James Cook University, PO Box 6811, Cairns, QLD 4870, Australia,
⁴King’s College London, Department of Geography, KCL, Strand, London, WC2R 2LS, UK and NERC National Centre for Earth Observation,
⁵Department of Ecology, Evolution, and Environmental Biology, Columbia University, New York, New York 10027, USA,
⁶Center for Environmental Sustainability, Earth Institute, Columbia University. Schermerhorn Extension, 1200 Amsterdam Avenue New York, NY 10027-5557, USA,
⁷Department of Geophysics and Meteorology, Bogor Agricultural University, Indonesia,
⁸Department of Ecology and Natural Resource Management (INA), Norwegian University of Life Science (NMBU), Box 5003, 1432A ° s, Norway.

Abstract:
Trans-boundary haze events in Southeast Asia are associated with large forest and peatland fires in Indonesia. These episodes of extreme air pollution usually occur during drought years induced by climate anomalies from the Pacific (El Nin˜o Southern Oscillation) and Indian Oceans (Indian Ocean Dipole).

However, in June 2013 – a non-drought year – Singapore’s 24-hr Pollutants Standards Index reached an all-time record 246 (rated ‘‘very unhealthy’’). Here, we show using remote sensing, rainfall records and other data, that the Indonesian fires behind the 2013 haze followed a two-month dry spell in a wetter-than-average year. These fires were short-lived (one week) and limited to a localized area in Central Sumatra (1.6% of Indonesia): burning an estimated 163,336 ha, including 137,044 ha (84%) on peat. Most burning was confined to deforested lands (82%; 133,216 ha). The greenhouse gas (GHG) emissions during this brief, localized event were considerable: 172 6 59 Tg CO_2-eq (or 31 6 12 Tg C), representing 5–10% of Indonesia’s mean annual GHG emissions for 2000–2005. Our observations show that extreme air pollution episodes in Southeast Asia are no longer restricted to drought years. We expect major haze events to be increasingly frequent because of ongoing deforestation of Indonesian peatlands.

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Supplementary Materials.