In Sumatra and Indonesia, seasonal fires and the thick smoke they produce plagued the islands for nearly two months in late 2006. Beginning in mid-September 2006, the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra and Aqua satellites detected numerous fires in daily images of the area. This image was captured by Aqua MODIS on November 5, 2006. Active fire locations are marked with red dots. Thick smoke spreads between the two islands, the grayish haze mingling with brighter clouds.
Many factors contribute to the fires, which usually start from agricultural burning, but often spread into adjacent tropical forest. When the forests have been degraded by logging, they become much more prone to fire. In addition, climate fluctuations, such as droughts that occur in concert with El Niño events, can make the fires worse. During droughts, the typically soggy forest floor of these lowland forests dries out. The thick layer of dead vegetation on the forest floor, peat, becomes flammable and produces enormous quantities of smoke when it burns.
Agricultural and forest fires burning on Sumatra and Borneo since late September 2006 blanketed a wide region with smoke that interrupted air and highway travel and pushed air quality to unhealthy levels. Fires were still burning in early November.