The haze affected Indonesia from at least late June,[1] to the end of October, turning into an international problem for other countries in September. It was the latest occurrence of the Southeast Asian haze, a long-term issue that occurs in varying intensity during every dry season in the region.[10] It was caused by forest fires resulting from slash-and-burn practices, principally on the Indonesian islands of Sumatra and Kalimantan, which then spread quickly in the dry season.[11][12][13][14][15][16][17][18][19]
More than 28 million people in Indonesia alone were affected by the crisis, and more than 140,000 reported respiratory illness.[9][26] According to a 2016 Harvard-Columbia University study, the haze caused more than 100,000 additional deaths, most of them (> 90,000) in Indonesia.[27][28] But later, the claim was refuted by Indonesia, Singapore and Malaysian health authorities.[29] The haze caused by the Indonesian forest fires has been shown to increase haze related illnesses, such as upper respiratory illnesses and acute conjunctivitis, in Singapore.[30]
The Indonesian government estimated that the haze crisis would cost it between 300 and 475 trillion rupiah (up to US$35 billion or S$47 billion) to mitigate.[31] School closures due to the haze were implemented in Indonesia, Malaysia and Singapore; these affected nearly four million students in Malaysia alone.[32][33][34] Among the events disrupted or even cancelled due to the haze were the 2015 FINA Swimming World Cup in Singapore and the Kuala Lumpur Marathon in Malaysia.
Heavy rains in Sumatra and Kalimantan in the last days of October 2015 significantly reduced the size and number of fires, and improved the air quality in most affected areas.[2][3][35][36] In turn, the NEA of Singapore stopped issuing haze advisories from 15 November 2015.
^Koplitz et al.: Public health impacts of the severe haze in Equatorial Asia in September–October 2015: demonstration of a new framework for informing fire management strategies to reduce downwind smoke exposure. Environmental Research Letters Vol. 11, No. 9, 2016, doi:10.1088/1748-9326/11/9/094023.