Smoke Blankets Borneo
The past few fire seasons in Indonesia have been pretty quiet, but a profusion of fire in Kalimantan, the Indonesian part of Borneo, and Sumatra in September 2019 has once again blanketed the region in a pall of thick, noxious smoke. Many schools have closed and several airports have canceled, diverted, or delayed flights in recent weeks as smoke lingered over the two islands, according to news reports.
The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite captured this image of Borneo on September 15, 2019. Smoke hovered over the islands and has triggered air quality alerts and health warnings in Indonesia and neighboring countries. Many of the fires were burning in Kalimantan, which is known for having extensive peat deposits, which are made up of a mixture of partly decayed plant materials formed in wetlands. Satellites have detected evidence of fires burning in this region throughout much of August, but the number and intensity of the fires increased in the first week of September.
Fires are a common occurrence in Kalimantan in September and October because farmers burn off agricultural and logging debris to clear the way for crops and livestock. In Kalimantan, the intent is often to prepare the land for new plantings of oil palm and acacia pulp. The Operational Land Imager (OLI) on Landsat 8 acquired the image below, which shows fires burning in several oil palm areas in southern Borneo. Shortwave-infrared observations have been overlain on a natural-color image to highlight the locations of active fires.
The map below shows organic carbon data from the GEOS forward processing (GEOS-FP) model, which assimilates information from satellite, aircraft, and ground-based observing systems. To simulate organic carbon, modelers make use of satellite observations of aerosols and fires. GEOS-FP also ingests meteorological data like air temperature, moisture, and winds to project the plume’s behavior. In this case, smoke has stayed relatively close to the source of the fires because winds have generally been gentle.
GEOS FP, like other weather and climate models, uses mathematical equations that represent physical processes to calculate what is happening in the atmosphere. The model calculates the position and concentration of organic carbon plumes every five minutes. The model ingests new aerosol data at three hour intervals, new meteorological data at six hour intervals, and new fire data on a daily basis.
Peat maps available through the Center for International Forestry Research’s Borneo Atlas indicate that many of the fires were burning in or near areas with underlain with peat — a mixture of partly decayed plant material formed in wetlands. Peat fires tend to be difficult to extinguish, often smoldering under the surface for months until wet season rains arrive.
Peat fires release large amounts of gases and particles, including carbon dioxide, methane, and fine particulate matter (PM2.5). Carbon dioxide and methane are potent greenhouse gases that warm the climate. PM2.5 is a mix of fine particulates known for having negative health effects.
PM2.5 — including types of aerosols called organic carbon and black carbon — are thought to be especially harmful because the particles are small enough to enter the lungs and bloodstream. Health research links exposure to black carbon to respiratory diseases, heart problems, and premature deaths. Evidence increasingly points to the toxicity of organic aerosols as well, though the health effects are less studied than some other particle types.
As he has done in past fire seasons, NASA Goddard Institute for Space Studies scientist Robert Field has been tracking the progression of the fire season in Indonesia. “They are really in the thick of another major event now. It is reminiscent of 2015, though buildup of smoke started a few weeks later this year because of rains in mid-August,” said Field, who is working on a project to better understand how various meteorological variables affect the likelihood that of vegetation burning. As part of that effort, he is also working on a NASA applied sciences project to integrate more satellite-based precipitation measurements into a fire danger monitoring system used by the Indonesian Meteorological, Climatological and Geophysical Agency.
“The fire counts from MODIS and VIIRS satellites have not been quite as high as they were in 2015 because of the late start, but the day-to-day increases in activity are now comparable to 2015,” said Field. “However, it is worth keeping in mind that many of these fires are burning underground or in areas with such thick smoke that satellites can’t detect them.”
During two past big fires years in Indonesia — 1997 and 2015 — El Niño conditions caused droughts that were major factors in exacerbating the fires. In 2019, El Niño conditions were neutral, but an oscillation of sea surface temperatures called the Indian Ocean Dipole appears to be responsible for the dry conditions this year, explained Field.