SINGAPORE - Since August, countries in South-east Asia, including Indonesia and Malaysia, have been choking in a blanket of persistent haze caused by raging fires in Indonesia.

Dense smoke haze has been seen over southern and central Sumatra and various parts of Kalimantan on most days since Aug 21.

Forest fires in Indonesia are more easily sparked during the ongoing dry season, which usually stretches from June to October. This year, the fire season is further worsened by a ‘Godzilla’ El Nino phenomenon, which makes the weather hotter and drier.

The confluence of these events have conjured flashbacks of the region’s worst air pollution incident in 2015.

That year was also an El Nino year, and the fires caused the Pollutant Standards Index (PSI) - a measure of air quality in Singapore - to soar above 300 in September, reaching hazardous levels and forcing schools to shut for a day. Half a million cases of respiratory infection were recorded in Indonesia then.

But weather experts told The Straits Times that a repeat of such a disaster this year seems unlikely, mainly because the onset of El Nino happened around June, later than the April onset in 2015. This means that the effects of this year’s El Nino will have a shorter overlap with the traditional dry season.

However, the severity of haze pollution experienced here can also be affected by other factors. The Straits Times speaks to weather and forestry experts on how the haze forecasts for the region could shape up.

What leads to haze over Singapore?

The severity of haze and when it occurs depends on the duration of dry weather, wind conditions and direction relative to the location of fires, the extent of burning, as well as measures taken on the ground to suppress fires, said the National Environment Agency (NEA).