Glacier variations and their response to climate change in an arid inland river basin of Northwest China

Glaciers are a critical freshwater resource of river recharge in arid areas around the world. In recent decades, glaciers have shown evidence of retreat due to climate change, and the accelerated ablation of glaciers and associated impacts on water resources have received widespread attention. Glacier variations result from climate change, so they can serve as an indicator of climate change. Considering the climatic differences in different elevation ranges, it is worthwhile to explore whether different responses exist between glacier area and air temperature in each elevation zone. In this study, we selected a typical arid inland river basin(Sugan Lake Basin) in the western Qilian Mountains of Northwest China to analyze the glacier variations and their response to climate change. The glacier area data from 1989 to 2016 were delineated using Landsat Thematic Mapper(TM), Enhanced TM+(ETM+) and Operational Land Imager(OLI) images. We compared the relationships between glacier area and air temperature at seven meteorological stations in the glacier-covered areas and in the Sugan Lake Basin, and further analyzed the relationship between glacier area and mean air temperature of the glacier surfaces in July–August in the elevation range of 4700–5500 m a.s.l. by the linear regression method and correlation analysis. In addition, based on the linear regression relationship established between glacier area and air temperature in each elevation zone, we predicted glacier areas under future climate scenarios during the periods of 2046–2065 and 2081–2100. The results indicate that the glaciers experienced a remarkable shrinkage from 1989 to 2016 with a shrinkage rate of –1.61 km2/a(–0.5%/a), and the rising temperature is the decisive factor dominating glacial retreat; there is a significant negative linear correlation between glacier area and mean air temperature of the glacier surfaces in July–August in each elevation zone from 1989 to 2016. The variations in glaciers are far less sensitive to changes in precipitation than to changes in air temperature. Due to the influence of climate and topographic conditions, the distribution of glacier area and the rate of glacier ablation first increased and then decreased in different elevation zones. The trend in glacier shrinkage will continue because air temperature will continue to increase in the future, and the result of glacier retreat in each elevation zone will be slightly slower than that in the entire study area. Quantitative glacier research can more accurately reflect the response of glacier variations to climate change, and the regression relationship can be used to predict the areas of glaciers under future climate scenarios. These conclusions can offer effective references for assessing glacier variations and their response to climate change in arid inland river basins in Northwest China as well as other similar regions in the world.     

Hydrological and water cycle processes of inland river basins in the arid region of Northwest China

The increasing shortage in water resources is a key factor affecting sustainable socio-economic development in the arid region of Northwest China(ARNC). Water shortages also affect the stability of the region's oasis ecosystem. This paper summarizes the hydrological processes and water cycle of inland river basins in the ARNC, focusing on the following aspects: the spatial-temporal features of water resources(including air water vapor resources, runoff, and glacial meltwater) and their driving forces; the characteristics of streamflow composition in the inland river basins; the characteristics and main controlling factors of baseflow in the inland rivers; and anticipated future changes in hydrological processes and water resources. The results indicate that:(1) although the runoff in most inland rivers in the ARNC showed a significant increasing trend, both the glaciated area and glacial ice reserves have been reduced in the mountains;(2) snow melt and glacier melt are extremely important hydrological processes in the ARNC, especially in the Kunlun and Tianshan mountains;(3) baseflow in the inland rivers of the ARNC is the result of climate change and human activities, with the main driving factors being the reduction in forest area and the over-exploitation and utilization of groundwater in the river basins; and(4) the contradictions among water resources, ecology and economy will further increase in the future. The findings of this study might also help strengthen the ecological, economic and social sustainable development in the study region.     

Economic losses from reduced freshwater under future climate scenarios: An example from the Urumqi River,Tianshan Mountains

As important freshwater resources in alpine basins, glaciers and snow cover tend to decline due to climate warming, thus affecting the amount of water available downstream and even regional economic development. However, impact assessments of the economic losses caused by reductions in freshwater supply are quite limited. This study aims to project changes in glacier meltwater and snowmelt of the Urumqi River in the Tianshan Mountains under future climate change scenarios (RCP2.6 (RCP, Representative Concentration Pathway), RCP4.5, and RCP8.5) by applying a hydrological model and estimate the economic losses from future meltwater reduction for industrial, agricultural, service, and domestic water uses combined with the present value method for the 2030s, 2050s, 2070s, and 2090s. The results indicate that total annual glacier meltwater and snowmelt will decrease by 65.6% and 74.5% under the RCP4.5 and RCP8.5 scenarios by the 2090s relative to the baseline period (1980-2010), respectively. Compared to the RCP2.6 scenario, the projected economic loss values of total water use from reduced glacier meltwater and snowmelt under the RCP8.5 scenario will increase by 435.10×10⁶ and 537.20×10⁶ CNY in the 2050s and 2090s, respectively, and the cumulative economic loss value for 2099 is approximately 2124.00×10⁶ CNY. We also find that the industrial and agricultural sectors would likely face the largest and smallest economic losses, respectively. The economic loss value of snowmelt in different sectorial sectors is greater than that of glacier meltwater. These findings highlight the need for climate mitigation actions, industrial transformation, and rational water allocation to be considered in decision-making in the Tianshan Mountains in the future.     

Glacier mass balance in High Mountain Asia inferred from a GRACE release-6 gravity solution for the period 2002–2016

We provide estimates of glacier mass changes in the High Mountain Asia (HMA) area from April2002 to August 2016 by employing a new version of gravity solutions of the Gravity Recovery and ClimateExperiment (GRACE) twin-satellite mission. We find a total mass loss trend of the HMA glaciers at a rateof –22.17 (±1.96) Gt/a. The largest mass loss rates of –7.02 (±0.94) and –6.73 (±0.78) Gt/a are found forthe glaciers in Nyainqentanglha Mountains and Eastern Himalayas, respectively. Although most glaciers inthe HMA area show a mass loss, we find a small glacier mass gain of 1.19 (±0.55) and 0.77 (±0.37) Gt/a inKarakoram Mountains and Western Kunlun Mountains, respectively. There is also a nearly zero massbalance in Pamirs. Our estimates of glacier mass change trends confirm previous results from the analysisof altimetry data of the ICESat (ICE, Cloud and Land Elevation Satellite) and ASTER (AdvancedSpaceborne Thermal Emission and Reflection Radiometer) DEM (Digital Elevation Model) satellites inmost of the selected glacier areas. However, they largely differ to previous GRACE-based studies which weattribute to our different post-processing techniques of the newer GRACE data. In addition, we explicitlyshow regional mass change features for both the interannual glacier mass changes and the 14-a averagedseasonal glacier mass changes. These changes can be explained in parts by total net precipitation (netsnowfall and net rainfall) and net snowfall, but mostly by total net radiation energy when compared to datafrom the ERA5-Land meteorological reanalysis. Moreover, nearly all the non-trend interannual masschanges and most seasonal mass changes can be explained by the total net radiation energy data. The massloss trends could be partly related to a heat effect due to increased net rainfall in Tianshan Mountains, QilianMountains, Nyainqentanglha Mountains and Eastern Himalayas. Our new results for the glacier mass changein this study could help improve the understanding of glacier variation in the HMA area and contribute tothe study of global change. They could also serve the utilization of water resources there and in neighboringareas.     

祁连山北大河流域冰川变化遥感监测

基于1956年地形图和2003年ASTER影像数据,在RS和GIS技术支持下,确定了1956年和2003年的冰川边界,对祁连山北大河流域冰川近47 a来的变化进行了研究。结果表明：该流域372条冰川面积在47 a间共减小了33.56 km²,平均每条减小0.09 km²,变化率-15.42%,冰川末端累计退缩51 015 m。分析显示,小冰川比大冰川消融的更快。对研究区附近气象站近年来的年平均气温、夏季平均气温和年降水量进行分析,认为气温升高是北大河流域冰川快速萎缩的主要原因。与中国西部其他冰川进行对比研究发现,北大河流域冰川消融速率比新疆要快,但较黑河流域及其他子流域要慢,初步推测是由冰川所在区域的气候及冰川自身因素共同作用的结果。     

近50年来新疆天山南北坡典型流域冰川与冰川水资源的变化

冰川是大自然修筑的"固体水库",在水资源的构成中占有重要地位。新疆地处内陆干旱区,是我国现代冰川面积分布最广的地区之一。冰川和冰川融水为新疆灌溉农业发展提供了可靠的水资源保障。本文根据中国冰川编目及近年来其它冰川研究成果和监测资料,对1960年以来新疆,主要是天山山区的冰川与冰川径流的变化进行了分析。分析表明,受全球气候变暖的影响,上世纪60年代以来至本世纪初,天山冰川的变化整体上以退缩为主,1963-2000年冰川面积平均减少12.5%。但受地理位置和地势条件的影响,不同流域的冰川变化存在着较大的区域性差异。随着冰川的强烈退缩和冰川融水的增加,使得近十余年来新疆天山地区大部分冰川补给河流径流量呈增加的趋势。     

近20 a中国天山东段典型冰川变化及其气候响应

冰川作为重要的淡水资源的存储体,也是气候变化的敏感"指示器"。在干旱半干旱区,冰川变化对人们的生产、生活和生态产生重要的影响。本文基于1990—2015年Landsat TM及ETM+遥感影像数据,利用雪盖指数法(NDSI)和阈值法,分析博格达峰及喀尔力克山的冰川面积变化,结合长时间序列的气温、降水数据分析天山东段典型冰川的气候响应。结果表明:(1)博格达峰与喀尔力克山的冰川均呈现退缩趋势,与气温和降水的变化趋势一致。(2)博格达峰和喀尔力克山冰川面积变化在东南坡向有波动增加趋势,其他坡向则未出现该现象。(3)从两个冰川不同坡向的面积和面积重心分布变化分析,博格达峰冰川面积在东坡方向退缩速率最大,而喀尔力克山的冰川在东北坡方向退缩速率最大。(4)根据栅格气象资料分析,近四五十年博格达地区冰川面积退缩速率大于喀尔力克山地区,并且博格达峰降水量的增加对冰川的退缩起到的作用不大,喀尔力克山的降水量对冰川面积的退缩起到了一定的抑制作用。(5)通过对博格达峰地区和喀尔力克山地区不同坡向的冰川面积与年均气温、年均降水量进行Person相关性分析,博格达峰地区、喀尔力克山地区各个坡向的冰川面积变化与降水相关系数均很小。但博格达峰地区北、东北、东南坡向的冰川面积与区域气温变化相关系数较高,喀尔力克山地区东南、东北坡向的冰川面积与区域气温的相关系数高且显著性明显。分析其原因,在年内尺度上,博格达峰地区、喀尔力克山地区是湿季气温升高所致,干湿两季降水量的增多,并没有使得冰川整体的退缩有所减缓。     

Spatiotemporal changes of typical glaciers and their responses to climate change in Xinjiang,Northwest China

Glaciers are highly sensitive to climate change and are undergoing significant changes in mid-latitudes. In this study, we analyzed the spatiotemporal changes of typical glaciers and their responses to climate change in the period of 1990-2015 in 4 different mountainous sub-regions in Xinjiang Uygur Autonomous Region of Northwest China: the Bogda Peak and Karlik Mountain sub-regions in the Tianshan Mountains; the Yinsugaiti Glacier sub-region in the Karakorum Mountains; and the Youyi Peak sub-region in the Altay Mountains. The standardized snow cover index (NDSI) and correlation analysis were used to reveal the glacier area changes in the 4 sub-regions from 1990 to 2015. Glacial areas in the Bogda Peak, Karlik Mountain, Yinsugaiti Glacier, and Youyi Peak sub-regions in the period of 1990-2015 decreased by 57.7, 369.1, 369.1, and 170.4 km², respectively. Analysis of glacier area center of gravity showed that quadrant changes of glacier areas in the 4 sub-regions moved towards the origin. Glacier area on the south aspect of the Karlik Mountain sub-region was larger than that on the north aspect, while glacier areas on the north aspect of the other 3 sub-regions were larger than those on the south aspect. Increased precipitation in the Karlik Mountain sub-region inhibited the retreat of glaciers to a certain extent. However, glacier area changes in the Bogda Peak and Youyi Peak sub-regions were not sensitive to the increased precipitation. On a seasonal time scale, glacier area changes in the Bogda Peak, Karlik Mountain, Yinsugaiti Glacier, and Youyi Peak sub-regions were mainly caused by accumulated temperature in the wet season; on an annual time scale, the correlation coefficient between glacier area and annual average temperature was -0.72 and passed the significance test at P<0.05 level in the Karlik Mountain sub-region. The findings of this study can provide a scientific basis for water resources management in the arid and semi-arid regions of Northwest China in the context of global warming.     

Five decades of glacier changes in the Hulugou Basin of central Qilian Mountains,Northwest China

The Heihe River Basin is the second largest inland river basin in the arid regions of Northwest China. Glaciers provide a large proportion of water resources for human production and living. Studies of glacier changes and their impact on water resources in the arid lands are of vital importance. A joint expedition was carried out in 2010 for investigating glaciers in the Hulugou Basin, which is located in the upper reaches of Heihe River. Therefore, glacier changes in the Hulugou Basin of central Qilian Mountains during the past 50 years were analyzed in this study by comparing topographic maps, satellite images, digital elevation models and field observation data from different periods. Results showed that the total area of the 6 glaciers in the Hulugou Basin decreased by 0.590±0.005 km2 during the period 1956–2011, corresponding to a loss of 40.7% over the total area in 1956. The average area reduction rate of the 6 glaciers is 0.011 km2/a. During the past five decades, the glacier shrinkage was accelerated. The changes in glacier ice surface elevation ranged from –15 to 3 m with an average thinning of 10±8 m or an annual decrease of 0.23±0.18 m(0.20±0.15 m/a water equivalent) for the period 1956–2000. The area of Shiyi Glacier in the Hulugou Basin decreased from 0.64 km2 in 1956 to 0.53 km2 in 2011 with a reduction rate of 17.2%. The Shiyi Glacier had been divided into two separated glaciers because of severe melting. Comparative analysis showed that glacier shrinkage in the Hulugou Basin is more serious than that in the other regions of Qilian Mountains.     

1957-2009年祁连山老虎沟流域冰川变化遥感研究

利用1:50000地形图,4期Landsat TM遥感影像及2009年RTK冰川边界测量结果,获得了1957-2009年间老虎沟冰川流域的面积变化特征,结合气候变化背景资料,探讨了冰川面积变化对气候变化的响应。结果表明:目视解译是老虎沟流域冰川变化遥感研究的最优方法;1957-2009年间老虎沟冰川面积共减少了11.59%,以1994-1999年间的缩减最为显著,1999-2009年间的变化次之,1957-1994年变化最小。冰川缩减率与气温增加值成正比,与冰川规模成反比。该结果为进一步丰富冰川变化及水资源研究奠定了基础,具有重要的科研价值和社会意义。     

Region-wide glacier area and mass budgets for the Shaksgam River Basin,Karakoram Mountains,during 2000–2016

The Karakoram Mountains are well known for their widespread surge-type glaciers and slight glacier mass gains.On the one hand,glaciers are one of the sensitive indicators of climate change,their area and thickness will adjust with climate change.On the other hand,glaciers provide freshwater resources for agricultural irrigation and hydroelectric generation in the downstream areas of the Shaksgam River Basin(SRB)in western China.The shrinkage of glaciers caused by climate change can significantly affect the security and sustainable development of regional water resources.In this study,we analyzed the changes in glacier area from 2000 to 2016 in the SRB using Landsat TM(Thematic Mapper)/ETM+(Enhanced Mapper Plus)/OLI(Operational Land Imager)images.It is shown that the SRB contained 472 glaciers,with an area of 1840.3 km2,in 2016.The glacier area decreased by 0.14%/a since 2000,and the shrinkage of glacier in the southeast,east and south directions were the most,while the northeast,north directions were the least.Debris-covered area accounted for 8.0%of the total glacier area.We estimated elevation and mass changes using the 1 arc-second SRTM(Shuttle Radar Topography Mission)DEM(Digital Elevation Model)(2000)and the resolution of 8 m HMA(High Mountain Asia)DEM(2016).An average thickness of 0.08(±0.03)m/a,or a slight mass increase of 0.06(±0.02)m w.e./a has been obtained since 2000.We found thinning was significantly lesser on the clean ice than the debris-covered ice.In addition,the elevation of glacier surface is spatially heterogeneous,showing that the accumulation of mass is dominant in high altitude regions,and the main mass loss is in low altitude regions,excluding the surge-type glacier.For surge-type glaciers,the mass may transfer from the reservoir to the receiving area rapidly when surges,then resulting in an advance of glacier terminus.The main surge mechanism is still unclear,it is worth noting that the surge did not increase the glacier mass in this study.     

Growth of the Sayram Lake and retreat of its water-supplying glaciers in the Tianshan Mountains from 1972 to 2011

Inland lakes and alpine glaciers are important constituents of water resources in arid and semiarid regions. Understanding their variations is critical for both an accurate evaluation of the dynamic changes of water resources and the retrieval of climatic information. On the basis of earlier researches, this study investigated the growth of the Sayram Lake and the retreat of its water-supplying glaciers in the Tianshan Mountains using long-term sequenced remote sensing images. Our results show that over the past 40 years, the surface area and the water level of the lake has increased by 12.0±0.3 km2 and 2.8 m, respectively, and the area of its water-supplying glaciers has decreased continuously since the early 1970 s with a total reduction of about –2.13±0.03 km2. Our study has indicative significance to the research of regional climate change.     

近23年来北天山冰川面积变化对气候的响应

利用1989、1998、2011年的Landsat TM、ETM+遥感影像为数据源,运用比值阈值法(b3/b5)结合目视解译方法,提取了北天山3个时段的冰川边界,并在地理信息系统技术支持下分析了该区域冰川的变化情况。研究表明:北天山整体变化幅度较大,冰川表现为萎缩的趋势,近23年来冰川面积减小了14.93%。分析认为,较大的变化率是由于研究区面积<1km2的冰川数量占总数的比重较大(近80%)造成的。同时分析了北天山冰川空间结构特征,<0.5km2面积的冰川对气候变化最为敏感,消融率最高,1～5km2面积的冰川对消融总量贡献比例最大。依据分形理论对未来冰川变化进行初步预测,分析认为研究区冰川的消融率仍保持比较高的状态。     

1960-2009年中国天山现代冰川末端变化特征

基于冰川定位观测、野外考察、航空摄影、遥感影像和地形图分析方法,研究了1960-2009年中国天山8条冰川末端变化特征。结果表明：1960-2009年,在天山地区气温与降水呈上升趋势的背景下,8条冰川均处于退缩状态,退缩速率由西向东逐渐减缓,其变化幅度因气候环境、地理位置、冰川规模和冰川形态等的不同而存在明显的区域性与阶段性差异。其中,乌鲁木齐河源1号冰川1962-1973年冰川末端退缩速率为5.96 m•a^-1,1973-1980年为3.28 m•a^-1,1980-1993年为3.93 m•a^-1,在1993年完全分离成东、西两支独立的冰川;博格达峰四工河4号冰川末端1962-1981年退缩速率为6 m•a^-1,1981-2006年为8.9 m•a^-1,2006-2009年为13.3 m•a^-1。表碛覆盖的青冰滩72号冰川和74号冰川末端1964-2009年退缩速率分别为41 m•a^-1和30 m•a^-1,远较无表碛覆盖的庙儿沟平顶冰川退缩迅速（1972-2007年冰川末端退缩速率为2.32 m•a^-1）。表面特征（表碛）亦是造成冰川变化差异的一个主要原因。     

1973-2010年布喀塔格峰冰川波动对气候变化的响应

通过遥感图像处理技术和目视解译方法提取1973-2010年位于昆仑山中段的布喀塔格峰冰川界限,用GIS分析近37a冰川面积变化,并系统地研究其对气候变化的响应情况。结果表明:1973-2010年布喀塔格峰冰帽表现先扩大(1973-1976年)后退缩(1976-2010年)趋势,总面积缩小了5.42%,每年退缩0.14%。分析1960-2010年研究区的气候变化特征,发现布喀塔格峰冰帽退缩的关键因素是气候变暖,年降水量的增加不能够抵消由夏季温度剧烈上升导致的冰川消融率,并且地形条件、地理位置以及冰川规模都是影响冰川波动的重要因素。     

近51a来乌鲁木齐河源区径流特征及对气候变化的响应

基于天山乌鲁木齐河源区1959-2009年的径流与气象记录,采用线性回归、M-K突变检验法和水量平衡模型分析了河源区气候、冰川及融水量的变化特征。研究发现:河源区冰川径流量与冰川物质平衡成负相关关系,过去51a间河源1号冰川融水径流共增加157.48×104m3,冰川融水径流量增加主要是由冰川退缩和降水量增加造成的。自20世纪90年代以后,冰川融水径流量增加显著,但整个河源区径流量却在减少,与气温升高导致蒸散能力增强、地下冰结构变化及冰川融水补给能力下降等有关。     

Climate change and its impacts on mountain glaciers during 1960-2017 in western China

Mountain glaciers are highly sensitive to climate change. In this paper, we systematically analyzed and discussed the responses of glaciers to climate change during 1960-2017 in western China by the methods of least squares and correlation analysis. Results show that the maximum temperature, minimum temperature, average temperature, and precipitation significantly increased in western China at the rates of 0.32°C/10a, 0.48°C/10a, 0.39°C/10a, and 11.20 mm/10a, respectively. However, the wind speed, hours of sunshine, snowfall, and snowy days displayed decreasing trends at the rates of -0.53 m/(s?10a), 3.72 h/10a, -2.90 mm/10a, and -0.10 d/10a, respectively. The annual percentage of glacier area decreased by approximately 0.42%, and the average glacier area decreased by 2.76 km²/a. Meanwhile, glacial shrinkages were greater in the Altay Mountains, Tanggula Mountains, and Qilian Mountains than in the other mountainous regions. Glacier accumulation decreased while melt volume increased at a rate of 2.7×10⁴ m³/a. The area of melt volume was 1.3 times that of the glacier accumulation area. The glacier mass balance (GMB) decreased substantially at a rate of -14.0 mm/a, whereas the equilibrium line altitude (ELA) showed an increasing trend at a rate of 0.5 mm/a. After 1997, the mass was smaller than -500.0 mm, indicating a huge loss in glaciers. Furthermore, relationships between ELA and GMB and various climatic factors were established. Temperature and precipitation demonstrated a significantly negative correlation, whereas wind speed and snowy days had significantly positive correlations with GMB. Snowy days also exhibited a remarkably negative correlation with ELA. The strong warming trend and less snowy days were thought to be the main factors leading to glacial melting, whereas the increase in precipitation, and reductions of sunshine hours and wind speed might slow glacial melting.     

哈密地区冰川变化趋势分析

雪冰融水是哈密地区地表径流的一种主要方式。受全球气候变暖的影响,哈密地区的冰川处于加速融化的阶段,水资源成为哈密地区发展的主要瓶颈。通过对哈密地区冰川物质平衡、面积、厚度、冰川区水文气象等参数的观测,预测冰川水文和水资源的变化,为更好地利用好哈密地区有限的水资源,为可持续发展,提出应对措施。     

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