Smoke Blankets the Amazon

Natural color

In the absence of human intervention, most of the forests in the Amazon River basin are too wet to burn. Yet for as long as scientists have observed the region by satellite, they have detected an abundance of fire activity, especially during the driest months of the year. This year has followed that pattern, with especially dense plumes of smoke streaming from fires near settlements and roads in the southern Amazon.

On September 5, 2022, the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite acquired a natural-color image (above) of smoke over parts of Bolivia and Brazil. Thick smoke emanated from Bolivia’s El Beni and Santa Cruz districts, where forests typically receive less rain than other parts of the Amazon basin. The smoke streamed north and mixed with plumes from fires burning in rainforests in several Brazilian states, including Acre, Amazonas, Rondônia, Pará, and Mato Grosso. Substantial fire activity in 2022 has occurred along key highways, notably BR-163 and the Trans-Amazonian highway in Pará and Amazonas (upper right of image).

The thickest smoke plumes amid the heavily forested (green) areas typically rise from deforestation fires. These are usually lit to dispose of piles of leftover wood, sometimes several months after forests have been bulldozed. Forest clearing for ranching and farming is common in both countries. Smaller smoke plumes in cleared, agricultural areas (brown) are typically grassland fires lit by ranchers and farmers to manage cattle pastures or croplands.

Human-caused deforestation and pasture fires sometimes escape control and spread unchecked. In wet parts of the Amazon, generally in the western and northern parts of the basin, this can lead to understory fires that smolder and spread along the forest floor. In drier areas, including the Chiquitano forests, Beni Savanna, and Chaco forests in Bolivia, fires tend to spread more quickly, burn hotter, produce more smoke, and can consume the forest canopy.

The second image above shows the same area using observations of shortwave infrared (SWIR) light from MODIS. In that map, each red dot depicts one “fire detection” observed by MODIS on September 5, 2022. A fire detection is a pixel in which the sensor and an algorithm sensed thermal anomalies indicative of fire activity during one of the satellite’s passes. Multiple fire detections can be generated by a single fire. (Note: The MODIS on Aqua does not detect every fire. It can miss some small fires or those burning under tree canopy. Aqua MODIS detects burning in the afternoon and does not capture fires that occur in the morning, evening, or overnight.)

Brazil’s National Institute for Space Research (INPE) uses MODIS observations to monitor daily fire activity in the Amazon; INPE scientists also maintain a record of MODIS fire detections that spans decades. The agency reported 226,677 Aqua MODIS fire detections throughout Amazon Basin countries between January 1 and September 12, 2022. Argentina, Bolivia, Colombia, Paraguay, and Venezuela all had more than 10,000 fire detections; Brazil had 117,436.

Brazil’s fire count in 2022 is the most since 2010, when INPE’s monitoring system reported 182,168 fire detections through September 12. From 2002 to 2006, dry weather and widespread deforestation led to particularly intense burning, with 127,000 to 189,000 fire detections in Brazil each year between January 1 and September 12, according to INPE data.

“We have seen plenty of fire activity in recent weeks, but we can’t yet say how the 2022 season will compare with other years,” said Alberto Setzer, a senior scientist at INPE. “The fire season in the southern Amazon doesn’t usually wind down until October or November. But already we see a familiar pattern: large numbers of fires are happening in the same areas where satellites have mapped deforestation in recent years.”

NASA Earth Observatory images by Joshua Stevens, using MODIS data from NASA EOSDIS LANCE and GIBS/Worldview. Story by Adam Voiland.

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