Most of that choking haze that engulfs South-East Asia annually comes from peatland catching fire during the dry season in the middle of the year. Not only is the smoke a huge health hazard but the fires also increase emissions of greenhouse gases across South-East Asia.
Peatland is wet and soggy in its natural state; once it dries out, it becomes highly flammable. Dry peatland, once set alight to clear it of vegetation, can burn for days or weeks, even smouldering unseen underground after the fire above has been extinguished.