A clear understanding of the changes of water resources under the background of environmental changes is of great significance for scientific management and utilization of water resources in China. This study systematically analyzed the spatial-temporal variations of surface water resources in China since 2000. Water vulnerability in current (2010s) and its trends from 2000 to late-2010s in different regions of China were also summarized. In addition, the correspondingly adaptive measures to counter regional risks to water resources were proposed. We concluded that the runoff of major rivers had been decreasing in eastern China and increasing in western China during 2000-2018. In the arid area of Northwest China, the alpine runoff has shown an overall upward trend since the late-1990s/early-2000s, with a 10%-25% increase caused by the increase of glacial meltwater and precipitation. While the runoff of each hydrological station in the 2000s-2010s was 34.7% lower than that in the 1950s-2010s on average. The increases in precipitation and glacial meltwater with global warming caused a rapid expansion of lakes in the Qinghai-Tibet Plateau and Xinjiang, thus leading to an increase in total area and water quantity of lakes in China from 1995 to 2015. The mean contribution rates of climate change and human activity to runoff change in river basins of China were 53.5% and 46.5%, respectively, during the period of 2000-2010s. The driving factor of runoff change in many river basins has gradually changed from climate change (1950s-2000) to human activity (2000-2018). During 2000-2018, the contributions of human activities to runoff change were 50%-80% in major rivers of eastern China. The vulnerability in most areas of Northwest China and North China is generally high, with the vulnerability index greater than 0.6. Comparatively, in Northeast, East, South, and Central China, it is lower or not vulnerable. In Southwest China, the vulnerability varies greatly with Yunnan and Sichuan relatively low while Chongqing and Guizhou relatively high. The precipitation increase, the application of water-saving technology, the establishment of flood control and drought relief engineering facilities, and the introduction of relevant policies and measures have helped to gradually reduce the vulnerability of water resources in most areas of North and Northwest China (except Xinjiang) from 2000 to 2010s. Water vulnerability has been increasing in southern China, caused by climate change and the development of industry and agriculture, which increases water resource exposure since 2000. Based on the typical risk factors and vulnerability characteristics of water resources in different regions, this study proposed some targeted adaptive measures correspondingly so as to scientifically deal with the problems of surface water resources in China.

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.

Non-growing season CO2 emissions from Arctic tundra remain a major uncertainty in forecasting climate change consequences of permafrost thaw. We present the first time series of soil and microbial CO2 emissions from a graminoid tundra based on year-round in situ measurements of the radiocarbon content of soil CO2 (Delta(CO2)-C-14) and of bulk soil C (Delta C-14), microbial activity, and temperature. Combining these data with land-atmosphere CO2 exchange allows estimates of the proportion and mean age of microbial CO2 emissions year-round. We observe a seasonal shift in emission sources from fresh carbon during the growing season (August Delta(CO2)-C-14 = 74 +/- 4.7 parts per thousand, 37% +/- 3.4% microbial, mean +/- se) to increasingly older soil carbon in fall and winter (March Delta(CO2)-C-14 = 22 +/- 1.3 parts per thousand, 47% +/- 8% microbial). Thus, rising soil temperatures and emissions during fall and winter are depleting aged soil carbon pools in the active layer and thawing permafrost and further accelerating climate change.

Ecological environment in the arid areas of Northwest China is very vulnerable. Ecological vulnerability is considered to be one of the important indicators to measure the status and evolutions of the regional ecological environment and has become a key measure in the study of ecological change. However, studies on the ecological vulnerability in the whole arid areas of Northwest China on the county scale are currently sparse. Here, according to vegetation, land use type, topography, climate and socio-economic data, we present the spatial and temporal evolution of ecological vulnerability in the arid areas of Northwest China over the period 2000-2018 by structuring a pressure (P)-sensitivity (S)-restoration (R) ecological vulnerability evaluation index system and using an ordered weighted average (OWA) model. Our results suggested that the overall ecological vulnerability in the arid areas of Northwest China was dominated by the severe level from 2000 to 2018 with an average multiyear ecological vulnerability index of 0.48, which appeared a slight downward trend with the implementation of ecological restoration measures. Ecological vulnerability exhibited a significant stepped differentiation feature, and the eastern and western regions were markedly lower than that of the central region. Gravity center of the ecological vulnerability index has a significant spatial difference, which developed in the shape of Z direction between Heshuo county and Tuokexun county. Our study revealed the dynamic changes of ecological vulnerability at the county scale and provided decision-making information for the formulation of targeted ecological vulnerability management measures. Under the background of climate change and the new normal of social economy, the dynamic monitoring of ecological vulnerability and effective identification of vulnerability factors still require in-depth research.

Climate change increases the risk of severe alterations to essential wildlife habitats. The Arctic fox (Vulpes lagopus (Linnaeus, 1758)) uses dens as shelters against cold temperatures and predators. These dens, needed for successful reproduction, are generally dug into the active layer on top of permafrost and reused across multiple generations. We assessed the vulnerability of Arctic fox dens to the increasing frequency of geohazards (thaw settlement, mass movements, and thermal erosion) that is arising from climate change. On Bylot Island (Nunavut, Canada) we developed, and calculated from field observations, a qualitative vulnerability index to geohazards for Arctic fox dens. Of the 106 dens studied, 14% were classified as highly vulnerable, whereas 17% and 69% had a moderate and low vulnerability, respectively. Vulnerability was not related to the probability of use for repro- duction. Although climate change will likely impact Arctic fox reproductive dens, such impact is not a major threat to foxes of Bylot Island. Our research provides the first insights into the climate-related geohazards potentially affecting Arctic fox ecology in the next decades. The developed method is flexible and could be applied to other locations or other species that complete their life cycle in permafrost regions.

Earth's cryosphere and biosphere are extremely sensitive to climate changes, and transitions in states could alter the carbon emission rate to the atmosphere. However, little is known about the climate sensitivities of frozen soil and vegetation production. Moreover, how does climate heterogeneity control the spatial patterns of such sensitivities, and influence regional vulnerability of both frozen soil and vegetation production? Such questions are critical to be answered. We compiled long-time-series dataset including frozen soil depth (FD), normalized difference vegetation index (NDVI), and temperature and precipitation across Tibetan Plateau to quantify their sensitivities. Results reveal large spatial heterogeneity in FD and NDVI sensitivities. Precipitation alleviated FD sensitivities to warming in the cold northeast zone but accelerated FD sensitivities to precipitation in the warm south and southeast. Meanwhile, the positive warming effect on the NDVI was largely offset by slow increase of precipitation. Areas with high FD decreasing rate were found in northeast, inland, and south and southeast zones. Predominate area across the nine eco-regions are characterized as medium FD decreasing rate, and are synchronized with positive NDVI response in inland and west Himalayas, but negative in northeast and south and southeast. Precipitation restriction on NDVI would be pronounced in moist south and southeast. Our study provides new information that makes a much-needed contribution to advancing our understandings of the effects of global climate change on cryosphere and biosphere, which has important implications for global climate and our ability to predict, and therefore prepare for, future global climatic changes. Our attempt confirms that the method we used could be used to identify climate sensitivity of permafrost based on substantial observation data on active layer dynamics in future.

Permafrost landscapes are particularly susceptible to the observed climate change due to the presence of ice in the ground. This paper presents the results of the mapping and assessment of landscapes and their vulnerability to potential human impact and further climate change in the remote region of Eastern Chukotka. The combination of field studies and remote sensing data analysis allowed us to identify the distribution of landscapes within the study polygon, reveal the factors determining their stability, and classify them by vulnerability to the external impacts using a hazard index, H. In total, 33 landscapes characterized by unique combinations of vegetation cover, soil type, relief, and ground composition were detected within the 172 km(2) study polygon. The most stable landscapes of the study polygon occupy 31.7% of the polygon area; they are the slopes and tops of mountains covered with stony-lichen tundra, alpine meadows, and the leveled summit areas of the fourth glacial-marine terrace. The most unstable areas cover 19.2% of the study area and are represented by depressions, drainage hollows, waterlogged areas, and places of caterpillar vehicle passage within the terraces and water-glacial plain. The methods of assessment and mapping of the landscape vulnerability presented in this study are quite flexible and can be adapted to other permafrost regions.

Glaciers are a reliable freshwater resource in arid regions of West China and the vulnerability of its changes is closely related to regional ecosystem services and economic sustainable development. Here, we took the Qilian Mountains as an example and analyzed the spatiotemporal characteristics of glacier changes from 1998 to 2018, based on remote sensing images and the Second Chinese Glacier Inventory. We estimated the basic organizational framework and evaluation index system of glacier change vulnerability from exposure, sensitivity and adaptability, which covered the factors of physical geography, population status and socio-economic level. We analyzed the spatial and temporal evolutions of glacier change vulnerability by using the vulnerability evaluation model. Our results suggested that: (1) Glacier area and volume decreased by 71.12 +/- 98.98 km(2) and 5.59 +/- 4.41 km(3), respectively, over the recent two decades, which mainly occurred at the altitude below 4800 m, with an area shrinking rate of 2.5%. In addition, glaciers in the northern aspect (northwest, north and northeast) had the largest area reduction. Different counties exhibited remarkable discrepancies in glacier area reduction, Tianjuan and Minle presented the maximum and minimum decrease, respectively. (2) Glacier change vulnerability level showed a decreasing trend in space from the central to the northwestern and southeastern regions with remarkable differences. Vulnerability level had increased significantly over time and was mainly concentrated in moderate, high and extreme levels with typical characteristics of phases and regional complexity. Our study can not only help to understand and master the impacts of recent glacier changes on natural and social aspects but also be conducive to evaluate the influences of glacier retreat on socio-economic developments in the future, thus providing references for formulating relevant countermeasures to achieve regional sustainable development.

The vulnerability studies of human infrastructure in high-mountain areas influenced by geomorphological hazards in a changing climate are a rather young research field. Especially in high-alpine regions vulnerability maps are often not available, particularly regarding hiking trails or climbing routes. In this paper we present a heuristic approach to create vulnerability maps for Alpine trails and routes in the Grossglockner-Pasterze area (47 degrees 05'N, 12 degrees 42'E), an high-mountain area ranging from about 2000-3798 m a.s.l.. Therefore, the hazard potential that arises from gravitational mass-movements (rock falls, debris falls, other denudative processes) has been modelled in a two step approach. In the first step, the potential source areas were detected using a Digital Elevation Model combined with different further sources of information such as a geological map and orthophotos. Based on the estimation of the volume of the mobilizable substrate - which largely depends on the active layer thickness of permafrost - the second step was carried out by calculating transport paths and dispersal of the downward-moving material. The process model is based on a mass-conserving multiple direction flow propagation algorithm. Both disposition and process model were set up for the current environmental conditions (2010) and for a future scenario (2030) that is driven by a moderate regional climate scenario. Based on the assessment of these processes, susceptibility maps were generated. In a final step, vulnerability maps were created by combining the susceptibility maps with the alpine infrastructure. Considering the length of the trails, 5.5 % are classified in higher hazard classes in 2030 compared to 2010. The presented maps display all known major vulnerable trail and route sections in the study area properly. Furthermore, the evaluation of the maps by local and regional authority experts showed satisfactory results. However, future adaptions of both models - disposition as well as process model - are desirable, especially by the inclusion of better input data based on more empirical information on the processes.