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This study advances the previous understanding of the role of climate variability on Indonesian fire activity, by considering (i) the presence of different types of El Nino and (ii) the interaction between El Nino and the Indian Ocean Dipole (IOD). We classify 12 El Nino events during 1979-2016 into Eastern Pacific (EP) and Central Pacific (CP) types (four and eight El Nino events, respectively) and analyze observational data of sea surface temperature, precipitation, drought code, biomass burning carbon emission, visibility, and aerosol optical depth accordingly. We find that more intense and prolonged Indonesian drought and fires occur in the EP type, during which the emitted carbon amounts almost double those in the CP type. By further separating the CP type El Nino according to the phase of the IOD, that is, positive and negative, we show that fire seasons with less burning intensity and shorter duration are predominantly associated with weakly positive or even negative phase of the IOD phenomena. Moreover, fire intensity exhibits geographic diversity: fires are always more intensive in southern Kalimantan than in southern Sumatra in all El Nino events, although it is less dry in the former region. The outcome of this study can be applied to drought early warning, fire management, and air quality forecast in Indonesia and adjacent areas by identifying the type of El Nino and the phase of the IOD in advance.

Plain Language Summary Indonesian fires are well known for their adverse impact on regional air quality and climate because they release massive amounts of greenhouse gases and aerosols into the atmosphere. This study advances the previous understanding of the role of climate variability on Indonesian fire activity, by considering (i) the presence of different types (or location) of El Nino events in the Pacific Ocean and (ii) the interaction between El Nino and the Indian Ocean Dipole (IOD) phenomena. As a result, we find that more intensive and prolonged Indonesian fires occur during canonical El Nino events when the location of maximum SST anomaly is near the eastern Pacific accompanied with a positive phase of IOD (e.g., in 2006). In contrast, weaker Indonesian drought and fires likely occur in the El Nino events when the location of maximum SST anomaly is near the central Pacific accompanied by a weakly positive or even negative phase of the IOD instead (e.g., in 2009). The outcome of this study can be applied to drought early warning, fire management, and air quality forecast in Indonesia and adjacent areas by identifying the type (or location) of El Nino and the phase (or sign) of IOD in advance.

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