In dry areas, a forest fire is often followed by a dust storm

About half of the world’s severe wildfires are followed by dust storms, in which the wind blows harmful soil particles, for example, mud upwards and sometimes moves hundreds of kilometers.

Yan Yu of Peking University and Paul Jennox of the US research institute NOAA drew this conclusion based on satellite images. Those images showed more than 150,000 wildfires worldwide from 2003 to 2020. Atmospheric researchers split their analysis Monday. natural earth sciences. This dust storm degrades air quality, as well as smoke and soot that are also released during wildfires.

Severe wildfires destroy vegetation and leave the soil dry. After that, the trees and shrubs no longer slow down the wind and there is nothing to hold the soil particles in place. For example, strong winds can blow and carry along soil particles of clay and silt (parasitic) with a size of about 20 micrometers. These storms can last from days to weeks.

150,000 satellite images

“Dust storms after wildfires have been observed locally on a few occasions, for example, America and Australia,” said Jennox, one of the authors. “However, it has not been studied worldwide.”

To change that, Yu and Ginoux analyzed 150,000 satellite images of wildfires from different parts of the world from 2003 to 2020. They only looked at severe wildfires: with at least 20 active fires within a radius of ten kilometers in seven days. Ginoux: „We analyzed satellite images of different colours. To detect fires, we looked into infrared rays that are invisible to the human eye, where heat sources are clearly visible. For differences in vegetation before and after the fire, we looked at images captured in visible green light. To see how soil moisture affects dust storms, we analyzed soil moisture using microwaves, light with a longer wavelength than red, green, and blue. To detect dust particles, we looked at a range of colors.

We’ve seen them almost everywhere: China, Spain and Australia

Paul Jennox NOAA

“It was a surprise to us that dust storms happen quite often after an intense wildfire, by at least half,” Ginoux continues. “And we’ve seen them almost everywhere in the world: China, Spain, Australia.”

How long dust storms last depends on the severity of the bushfires and how dry the soil is before the bushfires break out. The drier the ground, the longer the dust storm would last, even if the flames were intense. Water holds soil particles together, making them too heavy to kick in.

Half of the dust storms were seen in savannas, large grass plains, low vegetation and some trees. Ginoux: “After the severe wildfires here in California, you still have tree trunks slowing the wind. Farmland is always sprayed with water. But in the savannas there is mainly low vegetation with few trees. After a fire, all burned out. Plants are approx. Moreover, you mainly see these types of landscapes in dry areas.”

Dust storms, in turn, can lead to wildfires and new dust storms. Dust particles can end up in the air, where they absorb sunlight. Then the surrounding air heats up, so that water vapor does not condense into the atmosphere and rain does not occur. ”