30-meter resolution! New breakthrough in large-scale and high-resolution permafrost mapping in Northeast China

Do you know what permafrost is? As the name suggests, permafrost is a frozen layer of soil with a temperature of 0°C or below. There is ice in the soil layer, but no snow on the surface. Permafrost generally exists in high-latitude areas and high mountains and plateaus in mid- and low-latitude areas. The total area of ​​permafrost on Earth is about 35 million square kilometers, accounting for 25% of the total area of ​​the continent , which is a considerable proportion. Among them, Russia and Canada are the countries with the most widespread permafrost. China also has permafrost, mainly distributed in the northern part of Northeast China, the high mountainous areas of Northwest China and the Qinghai-Tibet Plateau.

Depending on the external climate conditions, some frozen soil will thaw periodically with the change of seasons. If the soil freezes in winter and melts completely in summer, this kind of frozen soil is called seasonal frozen soil. If the frozen soil is thicker, or the external temperature is low all year round, the frozen soil remains frozen for many years, or remains frozen for at least three consecutive years, this kind of frozen soil is called permafrost. Permafrost is generally thicker in high latitudes and high altitudes, and thinner in low latitudes and low altitudes. It gradually becomes thinner from high latitudes to low latitudes, and from high altitudes to low altitudes, and even disappears completely.

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There is a large amount of permafrost in Northeast my country. However, due to global warming and human activities, the surface temperature of the permafrost area in Northeast China, located on the southern edge of the Eurasian permafrost area, has gradually increased, the thickness of the frozen layer has gradually decreased, and the area of ​​permafrost has also been reduced year by year. But how much has it been reduced? Where is there still permafrost and where is it gone? Where is the thickness of permafrost? These situations are very unclear. There is a lack of permafrost thermal stability classification standards and mapping that can reflect the dynamic changes of permafrost in Northeast China. Until 2023, many research and engineering construction are still referring to the permafrost regional distribution map drawn by my country in the 1970s, which seriously restricts the development of regional basic scientific research and comprehensive planning and construction.

Recently, after nearly 10 years of investigation, observation and research, Professor Shan Wei's team from the Institute of Cold Regions Science and Engineering of Northeast Forestry University has completed the latest 30-meter resolution permafrost distribution and spatiotemporal change map of Northeast China , and published them in the international journals "Remote Sensing" and "Sustainable Development" under the titles of "Thermal State Map of Permafrost in Northeast China Based on Surface Freezing Number Model" and "Spatial Distribution and Variation Characteristics of Permafrost Temperature in Northeast China", marking a new breakthrough in large-scale, high-resolution permafrost mapping in Northeast China.

Professor Shan Wei's team analyzed the distribution and changes of the annual average surface temperature and surface freezing number (SFnc) from 2003 to 2019. The distribution map shows that there is no extremely stable permafrost area in Northeast my country. Due to the continuous rise in temperature, the distribution of stable permafrost is shrinking. In just 16 years from 2003 to 2019, the permafrost area has decreased from 327,700 square kilometers to 271,000 square kilometers; the area of ​​semi-stable permafrost has increased slightly, and the area of ​​transitional or unstable permafrost is also increasing.

The distribution characteristics of permafrost show that permafrost with lower temperatures is mainly distributed in the Greater Khingan Range, from the northernmost tip of Mohe to the Arshan in the middle of the Greater Khingan Range. From a local perspective, altitude is the main factor controlling the temperature of permafrost, but from an overall perspective, latitude is the main factor controlling the distribution of permafrost. The overall change characteristics of the thermal distribution of permafrost are: the southern boundary of the permafrost area moves northward, the thermal state of regional permafrost decreases, and the number of metastable, transitional or unstable permafrost areas increases after the permafrost thaws.

This research result can provide more detailed basic data for regional research on permafrost and environment in Northeast my country, and provide important data support for climate change feedback, natural disaster process research, and terrestrial ecosystem response warning and prevention in permafrost areas of Eurasia.

References

[1]https://doi.org/10.3390/su14138178

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This article is a work of Science Popularization China-Starry Sky Project

Produced by: Science Popularization Department of China Association for Science and Technology

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Author: Zeng Xinyue Popular science creator Reviewer: Zhang Yuxiu Associate Professor, School of Earth and Planetary Sciences, Chinese Academy of Sciences Editor: Zhong Yanping