Worldwide examination of glacier change is based on detailed observations from only a small number of glaciers. The ground-based detailed individual glacier monitoring is of strong need and extremely important in both regional and global scales. A long-term integrated multi-level monitoring has been carried out on Urumqi Glacier No. 1 (UG1) at the headwaters of the Urumqi River in the eastern Tianshan Mountains of Central Asia since 1959 by the Tianshan Glaciological Station, Chinese Acamedey of Sciences (CAS), and the glaciological datasets promise to be the best in China. The boundaries of all glacier zones moved up, resulting in a shrunk accumulation area. The stratigraphy features of the snowpack on the glacier were found to be significantly altered by climate warming. Mass balances of UG1 show accelerated mass loss since 1960, which were attributed to three mechanisms. The glacier has been contracting at an accelerated rate since 1962, resulting in a total reduction of 0.37 km(2) or 19.3% from 1962 to 2018. Glacier runoff measured at the UG1 hydrometeoro-logical station demonstrates a significant increase from 1959 to 2018 with a large interannual fluctuation, which is inversely correlated with the glacier's mass balance. This study analyzes on the changes in glacier zones, mass balance, area and length, and streamflow in the nival glacial catchment over the past 60 years. It provides critical insight into the processes and mechanisms of glacier recession in response to climate change. The results are not only representative of those glaciers in the Tianshan mountains, but also for the continental-type throughout the world. The direct observation data form an essential basis for evaluating mountain glacier changes and the impact of glacier shrinkage on water resources in the interior drainage rivers within the vast arid and semi-arid land in northwestern China as well as Central Asia.

As an icon of anthropogenic climate change, alpine glaciers are highly sensitive to climate change. However, there remain research gaps regarding trends in climate extremes in glacierized regions and their relationship with local glacier mass balance. In this study, these re-lationships and their underlying links were explored in a typical glacierized region in the Eastern Tianshan Mountains, China, from 1959 to 2018. All warm extremes exhibited increasing trends that intensified dramatically from the 1990s. Meanwhile, decreasing trends were found for all cold extremes except for the temperatures of the coldest days and coldest nights. All of the precipitation extremes demonstrated increasing trends, except for consecutive dry days and consecutive wet days. Statistically significant positive/negative correlations were detected between glacier mass balance and six warm extremes (TN90p, TX90p, SU99p, TR95p, TXx, and TNx)/four cold extremes (TN10p, TX10p, FD0, and ID0). Simulation results showed that the impact of the intensity/frequency of the warm extremes (TN90p, TX90p, SU99p, and TR95p) on glacier ablation was remarkable and the effect of the cold extremes (FD0 and ID0) on accumulation was also significant. Additionally, the increases in the intensity and frequency of most climate extremes seemed more remarkable in glacierized regions than in non-glacierized regions. Hence, studies on glacier-climate interactions should focus greater attention on the impacts of climate extremes on glacier evolution.

The glacier is a crucial freshwater resource in arid and semiarid regions, and the vulnerability of the glacier change is intimately linked to regional ecological services and socio-economic sustainability. Taking the Tianshan Mountains region in China as an example, a basic framework for studying the vulnerability of glacier change was constructed so as to address factors such as physical geography, population status, socio-economic level, agricultural development, and social services. The framework was based on key dimensions, that is, exposure, sensitivity, and adaptability, and this constituted a targeted evaluation index system. We examined the spatial structure and spatial autocorrelation of the glacier change vulnerability using ArcGIS and GeoDa software. The influence and interaction of natural, social, economic, population and other factors on glacier change adaptability was examined using the GeoDetector model. The results suggested the following: (1) The vulnerability level decreased from the western region to the eastern region with significant differences between the two regions. The eastern region had the lowest vulnerability, followed by the central region, and then western region which had the highest vulnerability. (2) Significant positive and negative correlations were found between exposure, sensitivity, and adaptability, indicating that the areas with high exposure and high sensitivity to glacier change tended to have a low adaptive capacity, which led to high vulnerability, and vice versa. (3) The spatial heterogeneity regarding the ability to cope with glacier change reflected the combined effects of the natural, social, economic, and demographic factors. Among them, factors such as the production value of secondary and tertiary industries, the urban population, urban fixed-asset investment, and the number of employees played major roles regarding the spatial heterogeneity of glacier change.

The impact of climate change on glaciers and the hydrological processes in the easternmost end of the eastern Tianshan Mountains has yet to be understood. This study investigated the glacier change (area, surface elevation and volume change) and analyzed the variation of the observed runoff series over the past four decades in the Yushugou Basin, Eastern Tianshan Mountains. The hydrological processes were also simulated through the HBV-light model to quantify the impact of climate change on the glacier and runoff. The results showed that the glacier area has decreased by 13% and the total volume has decreased by 0.018 km(3) over the past four decades. A significant increasing trend (p < 0.01) was detected for the annual runoff and monthly runoff (May to September; p < 0.01). The simulation results revealed that the Yushugou River was highly recharged by glacial runoff and a negative tendency was found for the glacier mass balance on the basin scale over the past 38 years. As a region with an extremely dry climate and the lowest precipitation in the Tianshan Mountains, the observation and simulation of glaciers is critical to the security assessment of local water resources.

The accumulation and ablation processes of seasonal snow significantly affect the land surface phenology in a mountainous ecosystem. However, the ability of snow to regulate the alpine land surface phenology in the arid regions is not well described in the context of climate change. The impact of snowpack changes on land surface phenology and its driving factors were investigated in the Tianshan Mountains using the land surface phenology metrics derived from satellited products and a snow dataset from downscaled regional climate model simulations covering the period from 1983 to 2015. The results demonstrated that the annual mean start of growing season (SOS) and length of growing season (LOS) experienced a significant (p < 0.05) decrease and increase with a rate of -2.45 days/decade and 2.98 days/decade, respectively. The significantly advanced SOS and increased LOS were mainly seen in the Western Tianshan Mountains and Ili Valley regions with elevations from 2500 to 3500 m a.s.l and below 3000 m a.s.l, respectively. During the early spring, the significant decline in snow cover fraction (SCF) could advance the SOS. In contrast, snowmelt amount and annual maximum snow water equivalent (SWE) have an almost equally substantial positive correlation with annual maximum vegetation greenness. In particular, the SOS of grassland was the most sensitive to variations of snow cover fraction during early spring than that of other vegetation types, and their strong relationship was mainly located at elevations from 1500 to 2500 m a.s.l. Its greenness was significantly controlled by the annual maximum snow water equivalent in all elevation bands. Both decreased SCF and increased temperature in the early spring caused a significant advance of the SOS, consequently prolonging the LOS. Meanwhile, more SWE and snowmelt amount could significantly promote vegetation greenness by regulating the soil moisture. The results can improve the understanding of the snow ecosystem services in the alpine regions under climate change.

Mountains form distinct geographical units with complex topographic and climatic features. Mountain ecosystems, especially those in arid and semi-arid regions, are likely to be strongly influenced by climate change. The NDVI-based vegetation response to climate change was analyzed in the Tianshan Mountains in China, one of the largest mountain systems of central Asia. Datasets, including the Normalized Difference Vegetation Index (NDVI), precipitation, soil moisture, and snow cover, were used to analyze spatial patterns of NDVI during 2001-2013. A trend test and correlation analysis were used to verify the results. Results showed that: (1) Spatial patterns of NDVI in the Tianshan Mountains revealed significant differences during 2001-2013. A decreasing trend appeared mainly in the Ili River Valley (<-0.005 NDVI/year), the Kaidu River (-0.01 to -0.005 NDVI/year), and Bogda Shan (-0.005 to 0 NDVI/year). NDVI in the western Tianshan Mountains, eastern and western Bogda Shan showed an increasing trend. (2) Spring NDVI in the Tianshan Mountains decreased, while summer NDVI increased during 2001-2013. (3) Spatial variations in vegetation dynamics were attributed to the interaction of the four spheres of the earth's system, hydrosphere-pedosphere-atmosphere-biosphere. The main contributors including temperature, precipitation, and soil moisture had a notable effect on variations in vegetation. (4) The snow cover in the mountains was crucial for vegetation growth, especially in the winter half of the year. Understanding the spatial characteristics of NDVI in mountains under the effects of climate change will underpin further study in this ecological environment.

Upfreezing is an important geomorphic process in the periglacial environment. It is a product of cold climate and thus an important part of the cryospheric processes. Based on the long-term positioning observations in the source area of the Urumqi River, this article represents an in-depth discussion of the characteristics of sorted circles and upfreezing mechanisms in the Tianshan Mountains. In the source area of the Urumqi River, the intensity of upfreezing is the highest within the top 25 cm near the surface, while targets with a diameter of 3 cm are least affected by upfreezing. There is no distinct difference between the centre with fine grains and the margin with coarse debris within the same sorted circle in terms of the intensity of upfreezing. The correlation analysis demonstrates that temperature plays an important role in upfreezing and the development of sorted circles. A long-time positioning observation of sorted circles reveals that periglacial landforms are sensitive to regional climate change and respond quickly to the temperature increase of the recent two decades. Enhanced upfreezing was found to be due to increased soil moisture content.