A month has passed since wildfires erupted simultaneously in Gyeongbuk, Gyeongnam, and Ulsan, and recovery efforts have begun in earnest. With significant time expected for the removal of burned dwellings and other facilities, the supply of temporary housing for affected residents is progressing slowly. Concerns about secondary damage, such as landslides, are also increasing ahead of the monsoon season. As accurate assessments of the wildfire damage scale continue to be released, it has been analyzed that the extent of this wildfire damage is much wider than initially predicted.

The satellite service corporation NaraSpace released an analysis of the wildfire damage in Gyeongnam’s Sancheong County, Gyeongbuk’s Uiseong County, and Ulsan’s Ulju County, where the response level was at the highest stage 3, following the wildfires that occurred in the Yeongnam region at the end of March.

According to the Korea Forest Service, the total number of wildfires in March was 147, most of which did not cause significant damage due to successful initial responses. However, wildfires that broke out from March 21 onward in Gyeongbuk, Gyeongnam, and Ulsan expanded due to strong winds, exacerbating the damage. In particular, the wildfires in Gyeongnam’s Sancheong and Gyeongbuk’s Uiseong worsened as they reignited.

On March 22, a medium-resolution imaging spectroradiometer (MODIS) on board the NASA Aqua satellite captured images of the Yeongnam forest fire. Smoke from a large fire is visible. /NASA

The damaged area increased 12 times in a week

The NaraSpace analysis team used images captured by the Earth observation satellite Sentinel-2, operated by the European Space Agency (ESA), to analyze accurate damage status and affected areas in the wildfire-affected regions. This satellite consists of two twin satellites that orbit 768 kilometers above the Earth, capturing the same location once every five days. Sentinel-2 is equipped with a camera sensor that recognizes objects on the ground with dimensions ranging from 10 to 60 meters as a point. It detects various light such as visible light, near-infrared, and shortwave infrared that reflect from the ground.

The areas of forest fires nationwide in March /Narspace

The wildfire that broke out in Sancheong County, Gyeongnam, on the afternoon of the 21st of last month spread to the nearby area of Hadong, worsening the damage. The Korea Forest Service announced on the 24th of the same month that the firefighting rate reached 70%, but after that, reignition occurred in various places, leading to an increase in the affected area. An analysis of satellite images revealed that the affected area in Sancheong was 15.29 square kilometers by the 24th. However, as the fire spread north and south, it was analyzed that the affected area increased to 21.63 square kilometers by the 1st. Of the regions that suffered wildfire damage, approximately 19% (4.13 square kilometers) experienced moderate to severe damage. In particular, it was found that the upper part of the trees, known as the canopy layer, was burned or damaged by heat. Damage to the tree bark or internal structure slows down growth and causes decay due to pathogen invasion.

On the afternoon of the 21st of last month, a forest fire that broke out in Sancheong County, Gyeongnam, spread to the nearby area of Hadong, increasing the damage. The Korea Forest Service stated that as of the 24th of the same month, the extinguishing rate had reached 70%, but afterward, reignition occurred in various places, indicating an increase in the area affected. An analysis of satellite images showed that by the 24th, the affected area in Sancheong was 15.29㎢. However, as the fire spread north and south, the affected area increased to 21.63㎢ on the 1st. /ESA, Narspace

In Uiseong, Gyeongbuk, the fire spread through strong winds to nearby areas such as Andong, Cheongsong, and Yeongdeok, causing significant damage. Uiseong experienced the most severe damage among the stage 3 wildfire areas. The wildfire that began in Uiseong on the 22nd of last month had not yet spread to other regions by the 24th. However, the fire rapidly spread beyond Andong to Cheongsong, Yeongyang, and Yeongdeok, propelled by westerly winds at 15 meters per second. Actual analysis of satellite images revealed that the wildfire damage area in Uiseong was approximately 68.91 square kilometers by the 24th, but the next image taken on the 1st showed this figure had surged 12 times to 844.04 square kilometers. The area that suffered moderate to severe damage was also calculated to be 285.37 square kilometers, a figure that is 33 times the area of Yeouido in Seoul (8.48 square kilometers), indicating a significantly high proportion of severe damage among the wildfire-affected areas.

On the 22nd of last month, a forest fire that started in Uiseong, Gyeongbuk, had not spread to other areas by the 24th. However, the fire has spread rapidly over 15m per second westward, confirming that it has moved beyond Andong to Cheongsong, Yeongyang, and Yeongdeok. /ESA, Narspace

The wildfire that occurred in Ulju County, Ulsan, on the afternoon of the 22nd of last month, was not extinguished until the 27th of the same month. Satellite analysis showed that the wildfire damage area in Ulsan was approximately 3.58 square kilometers by the 25th, which was relatively smaller than the damage in other areas where a stage 3 wildfire response was issued.

The affected area is wider than expected

The Korea Forest Service had previously reported that the estimated area impacted by the wildfire was 45,157 hectares (451.57 square kilometers) until recently. However, this analysis has confirmed that as of the 1st, a far larger area of 844.04 square kilometers in Uiseong and nearby areas was affected by the wildfires.

In relation to this, the government conducted field surveys of the wildfire damage area in two rounds, from the 28th of last month to the 8th of this month and from the 9th to the 15th. The Korea Forest Service publicly released revised results on the 18th that the area affected by the large wildfires in Gyeongbuk, Gyeongnam, and Ulsan amounted to 1,040 square kilometers (104,000 hectares). This is 2.2 times larger than the area initially reported by the Korea Forest Service immediately after the firefighting efforts. The provisional affected area by region is shown as 288.53 square kilometers in Uiseong, 267.09 square kilometers in Andong, 206.55 square kilometers in Cheongsong, 162.08 square kilometers in Yeongdeok, 24.03 square kilometers in Sancheong, 9.94 square kilometers in Hadong, and 11.90 square kilometers in Ulsan Ulju. This analysis result using satellite images captured during the same period is generally consistent.

On the afternoon of the 22nd of last month, a forest fire that broke out in Ulju County, Ulsan, had an extinguishing rate of 98% by the 25th, but the extinguishing work was only completed on the 27th. By the 25th, the affected area from the Ulsan forest fire was about 3.58㎢, which was relatively smaller than other areas where a stage 3 forest fire response was issued. /ESA, Narspace

The Korea Forest Service explained that the major discrepancy between the initial announcement of the wildfire area and recent survey results is due to the fast-moving fires caused by strong winds, which left no fire lines in the extinguished areas, and intense haze that made identifying fire lines difficult. The initially announced area of the wildfire impact zone was based on boundaries defined using helicopter and drone images and ground observations, which differs from the areas of wildfire damage identified through field surveys in purpose and methodology.

To accurately assess the scale of wildfire damage and potential economic losses, real-time identification of wildfire locations and affected areas is necessary. The analysis team used Fire Layer technology, which combines infrared and visible light bands to identify firefighting locations without physically visiting the site. By analyzing shortwave infrared (SWIR) radiation, it is possible to track whether fires occur in dense foliage that obscures views of the leaves and the direction of fire spread.

The analysis team utilized near-infrared (NIR) and shortwave infrared (SWIR) reflected from trees and vegetation to compute a value known as the Normalized Burn Ratio (NBR), confirming the area and intensity of wildfire damage. These two types of infrared are frequently used as indicators of forest and woodland conditions. When the forest is healthy, NIR shows high reflectivity while SWIR shows low reflectivity. Conversely, recent wildfire damage areas exhibit low NIR reflectivity and high SWIR reflectivity. By examining the differences in values before and after wildfire damage, it is possible to determine the areas and intensity of wildfire damage.

On the third day of the large forest fire in Uiseong County, Gyeongbuk, on the 24th of last month, a forest fire is spreading through the mountainsides of Jeomgok-myeon in Uiseong County due to strong winds. /Yonhap News

Trees damaged by wildfires require harvesting as natural recovery is difficult. Information on the distribution of wildfire damage intensity obtained from satellites is also useful for wildfire recovery planning. The analysis team noted that differences in NBR values can relatively accurately estimate the severity of wildfire damage.

The recent wildfires in the Yeongnam region have been recorded as the largest in history, exceeding four times the affected area of the East Coast wildfires in 2000 (237.94 square kilometers). Thirty residents of the affected area lost their lives, and 45 others were injured. In Andong, 1,379 buildings and dwellings were lost, 1,178 in Yeongdeok, 787 in Cheongsong, 351 in Uiseong, and 124 in Yeongyang, displacing 3,773 people overnight.

Areas affected by wildfires are exposed to secondary damage such as landslides and soil erosion during the rainy season. The Korea Forest Service completed emergency assessments of 4,207 landslide-prone areas from the 28th of last month to the 11th of this month, ahead of the rainy season. They announced plans to install 12 erosion control dams this year and to build an additional 91 dams starting next year.

References

NaraSpace Earthpaper, https://ep.naraspace.com/

With advancements in low-cost space launch vehicles and small satellite technology, we have entered an era of real-time observation of events occurring on Earth. Satellites are now utilized in various areas, including defense, monitoring disasters and calamities, damage assessments, and industrial trend analysis. ChosunBiz will publish a series of space journalism titled ‘The world viewed from satellites’ and ‘The economy viewed from satellites,’ integrating satellite service company NaraSpace and satellite imagery data with coverage in defense, industry, economy, society, and international affairs.