The widespread burning of lowland forests on Borneo, as seen in this image taken by the MODIS instrument on the Aqua satellite, is an annual, manmade occurrence. People use fires to manage agricultural lands, including large palm tree plantations. So too, there are other fires that are started accidentally during activities like logging and then quickly get out of control. Lightning strikes in dry, hot areas are also a cause for widespread fires as well.
In El Nino years, like the current one of 2015, Indonesia experiences lower than average rainfall which can turn in a severe drought. As the usually swampy forests dry out leaving behind a rich abundance of fire fuel in the form of peat, both intentional and accidental fires can quickly grow out of control. When peat dries it is quite flammable. Burning peat also generates a huge amount of thick, dark smoke. This thick smoke produced by these fires contributes to the greenhouse gas emissions worldwide.
NASA’s Aqua satellite collected this natural-color image with the Moderate Resolution Imaging Spectroradiometer, MODIS, instrument on September 08, 2015. Actively burning areas, detected by MODIS’s thermal bands, are outlined in red. NASA image courtesy Jeff Schmaltz LANCE/EOSDIS MODIS Rapid Response Team, GSFC. Caption by Lynn Jenner