Progress has been made in the study of long-term snow cover changes in high Asia where Xinjiang habitats are located

High Asia, refers to the central part of Asia centered on the Qinghai-Tibet Plateau in the high altitude area, roughly including the Himalayas, Nianqing Tanggula Mountains, Kunlun Mountains, Karakoram Mountains, Tianshan Mountains and other mountain systems, with a space span of 25 ° N-46 ° N, 64 ° E-106 ° E, known as the "third pole" of the earth and "Asian water tower", is the most abundant area of snow and glaciers in the polar region
.
Snow cover is an important component of the cryosphere in high Asia, and its changes directly affect the water balance and energy balance
in this region.
The IPCC's sixth assessment report pointed out that the greenhouse gases emitted by human activities have undoubtedly caused global warming, and the average rate of warming in the Asian region in recent decades is about twice the average rate of warming in China and even the
world in the same period.
Snow is sensitive to rising temperatures and is often used as an indicator
of climate change.
Identifying long-term changes in snow cover in high Asian regions is of great significance for the prevention of water disasters and the survival and social stability of
humans in the "Third Pole" region.

Analyzing changes in snow cover in high Asia from shorter time series sometimes leads to conclusions that are inconsistent with conventional assertions
.
Previous studies based on shorter time series have found no significant reduction in the area of high Asian snow cover, or even an increase in
snow duration.
In addition, numerous previous studies have observed that high mid- and high-altitude areas in Asia heat up faster than lower altitudes, but it is unclear
whether there is an altitude dependence on snow changes due to the lack of long-term snow cover data 。 In view of the above problems, the team of researchers Chen Yaning of the State Key Laboratory of Desert and Oasis Ecology, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, developed a long-term, high-quality, daily high Asian snow coverage (HMA SCE) product, which systematically studied the temporal and spatial changes
of snow accumulation indicators (SCA and SCP) in different sub-regions and different altitudes in high Asia in the past 40 years under the background of global climate change.
The following preliminary results were obtained:

Key Result 1: Daily cloud-free snow products (i.
e.
, HMA SCE products)
were developed in the High Asia region by integrating AVHRR CDR SR and existing snow products.
HMA SCE products cover the entire high Asian region, with a time range of 1982-2019 and a spatial resolution of 5 km
.
The accuracy of HMA SCE products has been verified by the snow depth data in the station, and the OA, PA and UA have reached 81.
99%, 84.
20% and 76.
39%
respectively.
In addition, the accuracy of HMA SCE products has also achieved considerable performance by being validated by finer resolution products (Landsat images and M*D10A1GL06 products) and can be used for future climate change studies
in high Asian cryospheres.

Key Outcome 2: Analysis of the long-term variation of snow cover indicators shows that between 1982 and 2018, the snow cover area (SCA) in high Asia showed a significant reduction trend (-0.
56% ^a-1), The Snow Days (SCD) has been shortened by 15.
5 days, the Snow Start Date (SOD) has been delayed by about 5.
6 days (it is worth mentioning that in recent years, SOD has shown a certain advance in the Tianshan area due to the cooling trend of autumn temperatures), and the Snow End Date (SED) has been advanced by about 10 days
.
The areas where SCA (SCD) has decreased significantly are mainly in the southeast of the Qinghai-Tibet Plateau, while SCA (SCD) has shown a slight upward trend
due to the unique seasonal cycle in the surrounding areas such as the Western Tianshan Mountains.
The sensitivity analysis results showed that the snow phenology (SCP) was more sensitive to temperature rise, with temperature contributing 77.
6% to SOD and 69.
8%,
respectively.

Main Result 3: There is an altitude dependence on SCD changes, that is, below 5000 meters, and the shortening rate of SCD increases with the increase of altitude
.
This phenomenon is related
to factors such as the characteristics of the region itself, the altitude dependence of warming (EDW), and the increase in black carbon.
It is worth mentioning that above 5000 meters, the SCD reduction trend is weakening, which may be related
to the absence of EDW phenomenon above 5000 meters.

The results were published in Science Bulletin under the title "The continuing shrinkage of snow cover in High Mountain Asia over the last four decades.
"
The first author of the paper is Dr.

Li Yupeng of the Xinjiang Institute of Biological Areas.
The research was funded by the National Natural Science Foundation of China
.

Article link: https://doi.
org/10.
1016/j.
scib.
2022.
09.
012

Data link: https://doi.
org/10.
57760/sciencedb.
j00076.
00112

Figure 1 Flowchart of the generation of high Asian snow products

Figure 2 Changes in the phenology of high Asian snow