Fire activity and smoke pollution in Indonesia under the influence of drought
induced by 2015 El-Niño episode(2015 年のエルニーニョに伴う干ばつのもとで発生したインドネシアの火災と煙汚染)
Radyan Putra Pradana
ABSTRACTDuring the 2015 dry season, there were massive forest fire events in Indonesia associated with theextremely dry condition due to the El-Niño event. Previous El-Niño episodes have caused forest fire events inSumatra and Kalimantan islands, that potentially alters the function of tropical forest from carbon sink to carbon
source. In addition, the fire can influence on hydrological cycle because low soil moisture could reduce
evapotranspiration and atmospheric moisture, resulting in inactive convection process and less precipitation.
Therefore, the synthetic study of fire events have collected global attention in recent years, especially after
1997/1998 El-Niño event brought considerable environmental and economic damages. This study aims to evaluate
the impact of the latest strong El-Niño episode in 2015 in comparison to past events to understand the drought andfire conditions under which they occurred. For this purpose, a long term reanalysis dataset, MERRA2, provided byNASA was utilized to examine the relationship between aerosol optical depth (AOD) and meteorological parameters
during 1980-2015. This study also used the Global Fire Emission Dataset version 4 (GFED4) to examine thebiomass burning carbon emissions during 1997-2015.
The fire and smoke pollution in 2015 had occurred repeatedly in southern Sumatra and south-central
Kalimantan. The fires often occur during abnormally dry years. Precipitation anomaly and sea surface temperature
anomaly over Indonesia show strong positive correlation over Indonesia region during July to October. This
indicates less precipitation and resulting drought condition was due to the lower than normal sea surface temperaturearound Indonesia which weakened the convective activity.
The most severe drought and forest fires during 2015 occurred in September and October. In September,precipitation decreased considerably and precipitation anomaly reached -3.1 mm/day relative to climatology inKalimantan. This probably contributes to 78.6 TgC of carbon emission and 0.71 of AOD. Meanwhile, in Sumatra it
was noted that precipitation anomaly decreases by -2.73 mm/day relative to climatology and contribute to 35.2 TgCemissions and 0.6 of AOD. In October, precipitation anomaly reached -2.71 mm/day relative to climatology inKalimantan, and contribute to 15.6 TgC of emission and 0.76 of AOD. In Sumatra the precipitation decreased by-3.78 mm/day and caused 16.1 TgC of emission and 0.90 of AOD.
The mean precipitation during July-October 2015 was the second lowest since 1997 both in Sumatra (4.85mm/day) and Kalimantan (2.94 mm/day). It was a favorable condition for fire and haze occurrence. Since 1997 theaerosol emission in 2015 (29.2 TgC) was the third highest after 1997 (95.6 TgC) and 2006 (29.8 TgC) events, andthe 2015 AOD (0.46) was fourth highest after 1997 (1.01), 2002 (0.6) and 2006 (0.51) in Kalimantan. Despite theemission in 2006 (16.2 TgC) was higher than in 2015 (16.1 TgC), the 2015 AOD (0.5) was higher than 2006 (0.46)
in Sumatra. This indicates that high emissions do not always accompany high AOD because of the dynamicaltransport of aerosols in the atmosphere.
The difference in fire environments between Sumatra and Kalimantan may be partly attributed to different
patterns of human activity and government policy. This study analyzed the drought as the preconditioning of the fireoccurrence. Further studies will be needed to clarify the contribution of local human activity as a trigger of fires.
Key words: El-Niño 2015, forest fire, biomass burning emission, aerosol optical depth (AOD), precipitation