Research on long-term snow cover changes in high Asia has been progressed

High Asia refers to the high-altitude area of central Asia centered on the Qinghai-Tibet Plateau, including the Himalayas, Nianqing Tanggula Mountain, Kunlun Mountain, Karakoram Mountain, Tianshan Mountains and other mountain systems, with a spatial span of 25°N-46°N, 64°E-106°E, known as the “third pole” of the earth, “Asian water tower”, is the richest area in addition to 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 the region. According to the IPCC Sixth Assessment Report, greenhouse gases emitted by human activities contribute to global warming, so the average warming rate in Asia in recent decades is about twice the average warming rate of China and the world in the same period. Snow cover is sensitive to warming and is often used as an indicator of climate change. Identifying long-term changes in snow cover in high Asia is important for preventing water disasters and human survival and social stability in the “Third Pole” region.

Analyzing snow cover changes in high Asia from shorter time series sometimes leads to conclusions that are inconsistent with traditional assertions. Previous studies based on shorter time series have found that the snow cover area in high Asia has not decreased significantly, and even shows a trend of increasing snow cover duration. In addition, previous studies have observed that high altitudes in high Asia warmed faster than at lower altitudes, but it is unclear whether there is an elevation dependence on snow cover changes due to the lack of long-term snow cover data. In response to the above problems, the team of Chen Yaning, a researcher at 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 cover (HMA SCE) product, explored the temporal and spatial changes of snow cover indicators (SCA and SCP) in different subregions and different altitudes in high Asia in the past 40 years under the background of global climate change, and obtained the following preliminary results: (1) The study integrates AVHRR CDR SR and existing snow products, developed daily cloud-free snow products (i.e. HMA SCE products) in high Asia. HMA SCE products cover the entire High Asia region with a time horizon of 1982-2019 and a spatial resolution of 5 km. The accuracy of HMA SCE products is verified by the snow depth data in the station, which reaches 81.99%, 84.20% and 76.39% in OA, PA and UA respectively. In addition, HMA SCE products are also highly accurate through finer resolution products (Landsat images and M*D10A1GL06 products) and can be used for future climate change studies in the high Asian cryosphere. (2) The analysis of the long-term changes of snow cover indicators shows that from 1982 to 2018, the snow cover area (SCA) in high Asia showed a significant reduction trend (-0.56% a-1), the number of snow cover days (SCD) decreased by 15.5 days, the snow cover start date (SOD) was delayed by about 5.6 days (in recent years, due to the cooling trend of autumn temperature, SOD showed a certain advance in the Tianshan region), and the snow cover end date (SED) was 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) in surrounding areas such as the West Tianshan Mountains show a slight upward trend due to unique seasonal cycles. The sensitivity analysis results showed that the snow cover phenology (SCP) was more sensitive to temperature rise, and the contribution of temperature to SOD and SED reached 77.6% and 69.8%, respectively. (3) There is an altitude dependence in SCD changes, that is, below 5000 meters, the shortening rate of SCD increases with the increase of altitude. This phenomenon is related to factors such as regional characteristics, altitude dependence (EDW) of warming and increased black carbon. Above 5000 meters, the SCD reduction trend weakens, which may be related to the absence of EDW above 5000 meters.

Figure 1.Flow chart of high Asian snow products

Figure 2.Changes in snow cover phenology in high Asia

The study, titled The continuing shrinkage of snow cover in High Mountain Asia over the last four decades, was published in Science Bulletin. The research work was supported by the National Natural Science Foundation of China. (Source: Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences)

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