In a new study, Harvard University researchers and their colleagues estimate that the 2015 smoke event caused upwards of 100,000 deaths across Indonesia, Malaysia, and Singapore.
During periods of extreme dry weather caused by El Niño and a phenomenon called the positive Indian Ocean Dipole, smoke emissions are considerably higher — either because farmers are taking advantage of the dry weather to burn more land or because once burning, the fires are more difficult to control. Although many fires burn in remote areas of Indonesia, prevailing winds can carry the smoke hundreds of miles to densely populated cities like Palembang in Sumatra, and Singapore and Kuala Lumpur.
The region experienced similar smoke conditions caused by El Niño in 2006 but the Harvard-led team found that deaths from air pollution more than doubled between the 2006 and 2015 events, from about 38,000 to about 100,000. This is largely because of where the fires burned in relation to population centers, and their intensity. Fires in southern Sumatra and nearby Jambi province turn out to be particularly deadly.
“Based on years of epidemiological research, we understand very well the relationship between pollution and mortality,” said Jonathan Buonocore, coauthor and research associate at the T.H. Chan School of Public Health. “We know for each incremental increase in air pollution, you get a certain incremental increase in mortality risk.”