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Journal of Geographical Sciences >

2018 , Vol. 28 >Issue 2: 206 - 220

DOI: https://doi.org/10.1007/s11442-018-1468-y

Research Articles

Glacier changes in the Qilian Mountains in the past half-century: Based on the revised First and Second Chinese Glacier Inventory

  • SUN Meiping , 1, 2 ,
  • LIU Shiyin , 2, 3 ,
  • YAO Xiaojun 1 ,
  • GUO Wanqin 2 ,
  • XU Junli 2
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  • 1. College of Geography and Environment Sciences, Northwest Normal University, Lanzhou 730070, China
  • 2. State Key Laboratory of Cryosphere Sciences, Northwest Institute of Eco-Environment and Resources, CAS, Lanzhou 730000, China
  • 3. Institute of International Rivers and Eco-Security, Yunnan University, Kunming 650091, China

Author: Sun Meiping (1981-), PhD and Associate Professor, specializing in the research of hydrological processes and climate change impact assessment. E-mail:

*Corresponding author: Liu Shiyin, Professor, E-mail: ; This paper has been published in Chinese and revised partially.

Received date: 2017-06-07

  Accepted date: 2017-07-20

  Online published: 2018-02-10

Supported by

National Natural Science Foundation of China, No.41261016, No.41561016

National Basic Work Program of MST, No.2013FY111400

Postdoctoral Science Foundation of China, No. 2015M572619

Opening Foundation Projection of State Key Laboratory of Cryosphere Sciences, CAS, No. SKLCS-OP-2016-10

Youth Scholar Scientific Capability Promoting Project of Northwest Normal University, No. NWNU-LKQN-14-4

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Journal of Geographical Sciences, All Rights Reserved
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Abstract

Glaciers are the most important fresh-water resources in arid and semi-arid regions of western China. According to the Second Chinese Glacier Inventory (SCGI), primarily compiled from Landsat TM/ETM+ images, the Qilian Mountains had 2684 glaciers covering an area of 1597.81±70.30 km2 and an ice volume of ~84.48 km3 from 2005 to 2010. While most glaciers are small (85.66% are <1.0 km2), some larger ones (12.74% in the range 1.0-5.0 km2) cover 42.44% of the total glacier area. The Laohugou Glacier No.12 (20.42 km2) located on the north slope of the Daxue Range is the only glacier >20 km2 in the Qilian Mountains. Median glacier elevation was 4972.7 m and gradually increased from east to west. Glaciers in the Qilian Mountains are distributed in Gansu and Qinghai provinces, which have 1492 glaciers (760.96 km2) and 1192 glaciers (836.85 km2), respectively. The Shule River basin contains the most glaciers in both area and volume. However, the Heihe River, the second largest inland river in China, has the minimum average glacier area. A comparison of glaciers from the SCGI and revised glacier inventory based on topographic maps and aerial photos taken from 1956 to 1983 indicate that all glaciers have receded, which is consistent with other mountain and plateau areas in western China. In the past half-century, the area and volume of glaciers decreased by 420.81 km2 (-20.88%) and 21.63 km3 (-20.26%), respectively. Glaciers with areas <1.0 km2 decreased the most in number and area recession. Due to glacier shrinkage, glaciers below 4000 m completely disappeared. Glacier changes in the Qilian Mountains presented a clear longitudinal zonality, i.e., the glaciers rapidly shrank in the east but slowly in the central-west. The primary cause of glacier recession was warming temperatures, which was slightly mitigated with increased precipitation.

Key words： glacier change; glacier inventory; glacier volume; climate change; Qilian Mountains

Cite this article

SUN Meiping , LIU Shiyin , YAO Xiaojun , GUO Wanqin , XU Junli . Glacier changes in the Qilian Mountains in the past half-century: Based on the revised First and Second Chinese Glacier Inventory[J]. Journal of Geographical Sciences, 2018 , 28(2) : 206 -220 . DOI: 10.1007/s11442-018-1468-y

1 Introduction

Alpine glaciers are important components of the cryosphere (Kargel et al., 2014), act as natural recorders and indicators of climate change (Orelemans et al., 1998; Shi and Liu, 2000), and are important water resources as “alpine solid reservoirs” (Xie et al., 2005). As the country with the most alpine glaciers in the mid-low latitude regions of the world, China has 48571 glaciers covering a total area of 5.18×104 km2, which accounts for 7.1% of the world glacier area outside the Antarctic and Greenland (Liu et al., 2015). Glaciers and glacial meltwater are the most important fresh-water resources and play critical roles in maintaining fragile ecological balance and sustainable development of socio-economic activities in western China, especially in arid and semi-arid regions (Liu et al., 1999; Zhang et al., 2012). The Hexi Corridor, nurtured by glacial meltwater from the Qilian Mountains, is an important route for trade and cultural communication connecting Europe and Asia, and constitutes part of the Silk Road Economic Belt. Therefore, glacier changes in the Qilian Mountains have a great significance for Gansu and Qinghai provinces, and the entire nation.
Similar to glacier changes in western China, glaciers are in a state of mass loss, recession and thinning in the Qilian Mountains due to climate warming (Liu et al., 1999; Zhang M J et al., 2011; Wang et al., 2013). From the Little Ice Age (LIA) to 1990, the glaciers in the western Qilian Mountains generally receded; glacier area and volume has been characterized by larger reductions in the south and east compared to the north and west. About 95% of glaciers receded at a rate of ~419 m/a during the period 1956-2000 (Liu et al., 2002; Liu et al., 2006). The area of glaciers in the central Qilian Mountains decreased 21.7% from 1956 to 2003, and glacier areas reduced 29.6% and 18.7% in the Heihe River and Beida River basins, respectively (Chen et al., 2013). Bie et al. (2013) showed that the area of glaciers in the Heihe River basin decreased 138.90 km2 (-35.6%) from 1960 to 2010 and hypothesized that glaciers in this region were an intensive recessional type. Glaciers in the Lenglongling range, located in the eastern Qilian Mountains, also showed an overall recession, with some glaciers disappearing completely (Cao et al., 2010; Zhang et al., 2010). Tian et al. (2014) indicated that glaciers had an accelerated retreat in the Qilian Mountains since the 1990s. Based on Shuttle Radar Topography Mission (SRTM) and Ice, Cloud, and land Elevation Satellite (ICESat) data, Wang et al. (2013) calculated glacier volume loss in the Qilian Mountains and estimated an annual mass loss of 534.2 ± 399.5 × 106 m3 w.e. at the beginning of the 21st century, which clearly has high uncertainty. Due to the different data sources adopted by scholars and the study period, together with the area error in the First Chinese Glacier Inventory (FCGI) and complexity of glacier interpretation based on remote sensing (Paul et al., 2010; Yao et al., 2012), a more systematic study of glacier change and regional differentiation is necessary for the Qilian Mountains. Based on the revised FCGI and latest Second Chinese Glacier Inventory (SCGI) datasets, this paper analyzes glacier change in the Qilian Mountains for the past half-century. Furthermore, the study characterizes glacier change and provides a basis for rational utilization of water resources in this region.

2 Study area

The Qianlian Mountains (36°30′-39°30′N, 93°30′-103°00′E) are located in the northeastern margin of the Tibetan Plateau and are composed of a series of parallel mountains and valleys with a NW trend (Figure 1). Starting from Wushaoling in the east and ending at Dangjin Shankou (Pass) in the west, and stretching from the Hexi Corridor to the Qaidam Basin along the north-south direction, the Qilian Mountains have an approximate length of 800 km and width of 300 km (You and Yang, 2013). The Qilian Mountains are divided into three parts: eastern (Wuwei-Laji Mountain), central (Jiuquan-Delingha), and western (Yingzui Mountain-Da Qaidam), and are bounded by Qinghai Lake and Har Lake to the southwest (Wang et al., 1981). The terrain gradually rises from northeast to southwest, with Mount Tuanjie as the highest peak (also known as Kangze’gyai, 5826 m). This region has a plateau continental climate; the western region is controlled by westerly winds and the eastern region is influenced by the southeast and southwest monsoons. The annual average temperature is 5°C and annual precipitation is 250 mm. The precipitation mainly occurs in summer and gradually decreases from east to west.
Figure 1 The distribution of glaciers in the Qilian Mountains
According to the SCGI, in the Qilian Mountains, there are 2683 glaciers with an area of 1597.81 km2, accounting for 3.09% of total glacier area in China, and ranking 9th out of the 14 mountains and plateaus in western China with glaciers (Liu et al., 2015). Glacier types include continental glaciers in the central and eastern regions and polar glaciers in the western region (Shi and Liu, 2000). In the SCGI, glaciers in the Qilian Mountains are categorized by region: the Hexi (5Y4) and Qaidam (5Y5) interior areas of the Eastern Asia interior drainage (5Y), and Datong River basin (5J4) of the Yellow River exterior drainage (5J) (Shi, 2005). Specifically, the Hexi interior area includes the Shiyang, Heihe, Beida, Shule, and Danghe rivers located in the northern Qilian Mountains, and the Qaidam interior area includes the Haltang, Iqe, Tatalin Gol, Bayan Gol, and Buh rivers in the south.

3 Data and methods

3.1 Data sources

In the FCGI dataset for the Qilian Mountains published in 1981, the number and area of glaciers were manually derived from aerial topographic maps in the 1960s (Wang et al., 1981). In this study, the same aerial topographic maps used in the FCGI and other maps from different periods were collected to digitalize glacier boundaries. The data sources used in the revised FCGI dataset included 46 topographic maps with a scale of 1:100,000 and 18 topographic maps with a scale of 1:50,000. Furthermore, they were classified into three periods: 1956-1957, 1966-1978, and 1983. The area of glaciers illustrated in topographic maps from 1956, 1957, 1966, 1973, and 1975 accounted for ~90% of the total area of glaciers in the Qilian Mountains. The data sources adopted in the SCGI dataset were 16 Landsat TM/ETM+ remote sensing images with little cloud and snow cover; the path/row numbers were 132034, 133033, 134033, 134034, 135033, 135034, 136033, 136034, and 137033 and were freely downloaded from the USGS website (http://glovis.usgs.gov). The months of these remote sensing images were mainly concentrated in June-September from 2005 to 2009.
The digital elevation model (DEM) data used in the revised FCGI and SCGI were topographic maps and SRTM V4.1, respectively. The latter was provided by the Consultative Group on International Agricultural Research (CGIAR, http://srtm.csi.cgiar.org). The annual temperature and precipitation data in the Qilian Mountains for the period 1961-2010 were extracted from the 0.5°×0.5° gridded dataset for monthly temperature and precipitation in China provided by the China Meteorological Data Service Center (http://data.cma.cn).

3.2 Glacier inventory

According to the World Glacier Inventory (WGI), the FCGI dataset for the Qilian Mountains was completed from 1979 to 1980 by Chinese glaciologists (Wang et al., 1981). However, limited by technological conditions at that time, the area of each glacier was manually measured using the grid method or planimeter instrument, which has a worse precision than values calculated using GIS software (Yao et al., 2012). To improve the accuracy of glacier area and provide a comparison with the SCGI dataset, the manual digitalization method was adopted to revise the FCGI dataset. Procedures included scanning topographic maps, geometric rectification, heads-up digitalizing, calculating the geometric parameters of a glacier, and artificial verification of each glacier’s attributes. The statistics from the revised FCGI dataset demonstrated that there were 3000 glaciers with an area of 2014.96 km2 in the Qilian Mountains, which is larger than the previous result, i.e., the original number of glaciers was 2815 with an area of 1931 km2 (Wang et al., 1981). The methods used in the SCGI dataset have been described in detail by Liu et al. (2015) and Guo et al. (2015).

3.3 Error estimation

There are usually two methods to estimate the error in glacial extent based on artificial visual interpretation. One is field investigation and the other is a comparison with high-resolution remote sensing images (Yan and Wang, 2013). Due to the steep terrain and severe climate in the glaciated region, it is very difficult to verify the interpretation precision of glaciers using field investigation. Therefore, the latter method has been widely adopted for error estimation of glacier interpretation based on remote sensing images (Racoviteanu et al., 2009; Kargel et al., 2014). For the SCGI dataset, experienced researchers manually revised the boundaries of automatically derived glaciers (Liu et al., 2015). Although the SCGI dataset was created using visual interpretation that can be viewed as true glacier values, there were still some errors, such as the offset of pixel. In this study, the errors caused by spatial resolution of topographic maps and satellite remote sensing images were considered, which are calculated with the following formula:
ε=N·A/2 (1)
where ε is the error (m2); N is the number of pixels located in the boundary of glacier; A is the size of glacier boundary symbol on the topographic map or the area of one pixel in the remote sensing image, which are 729 m2 for a topographic map with a scale of 1:100,000 and 900 m2 for Landsat TM/ETM+ images, respectively. The results showed that the errors in glacier area in the FCGI and SCGI datasets for the Qilian Mountains due to image spatial resolution were ±105.90 km2 (±5.26%) and ±70.30 km2 (±4.40%), respectively.

3.4 Methods for calculating glacier area change

The change in glacier area was defined as the difference between the corresponding glacier areas in the FCGI and SCGI datasets. Due to the time span in the FCGI dataset, two methods, the rate and relative rate of glacier area change, were proposed to compare the glacier change in different basins, which are calculated as follows:
${{V}_{GAC}}=\frac{G{{A}_{s}}-G{{A}_{f}}}{{{Y}_{f-s}}}$ (2)
$P{{V}_{GAC}}=\left[ {{\left( \frac{G{{A}_{s}}}{G{{A}_{f}}} \right)}^{1/{{Y}_{f-s}}}}-1 \right]\times 100%$ (3)
where VGAC is the rate of glacier area change (km2×a‒1); PVGAC is the relative rate of glacier area change (%×a‒1); and GAs and GAf are glacier areas (km2) in the SCGI and FCGI, respectively. Yf‒s is the time interval (a, year) between the FCGI and SCGI, which can be obtained from the following formula:
${{Y}_{f-s}}=\frac{\sum\limits_{i=1}^{m}{{{A}_{i}}\cdot {{Y}_{i}}}}{\sum\limits_{i=1}^{m}{{{A}_{i}}}}-\frac{\sum\limits_{j=1}^{n}{{{A}_{j}}\cdot {{Y}_{j}}}}{\sum\limits_{j=1}^{n}{{{A}_{j}}}}$ (4)
where Ai and Yi are the area of glacier i and its acquisition year in a basin in the SCGI dataset, respectively; Aj and Yj are the area of glacier j and its acquisition year in this basin in the FCGI dataset, respectively; and m and n are the total number of glaciers in the basin in the SCGI and FCGI datasets, respectively.

3.5 Methods for calculating ice volume

Measurements of glacier thickness by GPR or drilling have only been conducted on a few glaciers; therefore, calculating glacier ice volume over a wide area depends on empirical formulas (Gärtner-Roer et al., 2014). The ice volume-area relation for a glacier is generally expressed using:
V=cAλ (5)
where V denotes the ice volume of glacier (km3); A is the area of glacier (km2); and c and λ are empirical coefficients. In this study, the values of c and λ proposed by Radić and Hock (2010), Grinsted (2013) and Liu et al. (2003) were adopted.

4 Results and discussion

4.1 The contemporary distribution of glaciers in the Qilian Mountains

4.1.1 General glacier characteristics
There were 2684 glaciers with an area of 1597.81 km2 and ice volume of 88.48 km3 in the Qilian Mountains during the period 2005-2010. As shown in Figure 2, a clear feature of glaciers in the Qilian Mountains was that glaciers with areas <1.0 km2 accounted for the largest number of glaciers, while glaciers with areas in the range of 1.0-5.0 km2 accounted for the most glacierized area. Specifically, there were 2299 glaciers with areas <1.0 km2, which accounted for 85.66% of the total number of glaciers in the Qilian Mountains. As glacier size increased, the number of glaciers rapidly decreased. There was only one glacier with an area >20 km2, Laohugou Glacier No.12, with an area of 20.42 km2. The area of glaciers appeared to have a normal distribution. Glaciers classified with areas between 2.0 km2 and 5.0 km2 accounted for the largest area (372.37 km2); glaciers classified with areas between 1.0 km2 and 2.0 km2 accounted for the second largest area, 305.67 km2. Together, these two area classes accounted for 42.44% of the total glacierized area in the Qilian Mountains. There were 858 glaciers with areas <0.1 km2, which had a total area of 41.50 km2 (2.60% of total glacierized area); this was approximately double the area of Laohugou Glacier No.12.
Figure 2 The total glacierized area and number of glaciers in different size classes in the Qilian Mountains between 2005 and 2010
4.1.2 Glacier altitude distribution
The primary terrain factors that influence the number and size of glaciers are the absolute elevation of the host mountain and relative elevation above the equilibrium line (Shi, 2000). Due to geologic structures and tectonics, the elevation gradually decreases from southwest to northeast in the Qilian Mountains. Although 30% of the mountainous area in the Qilian Mountains is above 4000 m, the glacierized area above the same altitude only occupies 1.29% of the total alpine area, which implies that it is poorly suited for glacier development. In general, the Qilian Mountains are divided into five sub-regions: (1) alpine and gorge region in the north, (2) alpine region upstream of the Shule and Danghe rivers, (3) moderately eroded alpine and valley region in the south, (4) alpine and basin region around Qinghai and Har lakes, and (5) strongly eroded valley region close to the Huang River. Due to high relief, strong erosion, and broken surfaces, glacier areas were usually smaller in the first sub-region. However, in the second sub-region, glaciers had larger areas and formed larger glaciated regions around the main peak in the Daxue, Shulenan, and Tergun Daban mountains with good terrain conditions for glacier development. The altitude in the fifth sub-region was very low, so there were no glaciers.
The statistical analysis based on an altitude interval of 50 m showed that the hypsography of the glacier area in the Qilian Mountains was in normal distribution (Figure 3). Glaciers developed in the elevation band of 4000- 5800 m, and glaciers located between 4800 and 5200 m. formed the main glacier bodies, accounting for 58.15% of the total area of glaciers. The glacier terminus with the lowest altitude (38°17′N, 100°19′E, 4017.8 m) was located in the Panjia River basin (5Y422F) on the north side of Tulai Mountain. Affected by parallel mountains and valleys with NW orientation, the median altitude of glaciers gradually rose from 4483.8 to 4820.2 m. along the Lenglongling, Zoulangnan, and Tulai mountains in the EW direction, which is similar to the trend in the equilibrium-line altitude (ELA) for the Qilian Mountains proposed by Su et al. (2014). The median altitudes of glaciers were between 5003.7 and 5097.2 m. in the wide western alpine region, including the Daxue, Shulenan, Danghenan, and Tergun Daban mountains. The highest median altitude (5234.1 m) of glaciers was located in the Qaidam Mountains.
Figure 3 Hypsography of glacier area in the Qilian Mountains
4.1.3 The distribution of glaciers in different drainage systems
As described in Section 2, glaciers in the Qilian Mountains were assigned to three drainage basins, categorized as 5Y4, 5Y5, and 5J4. Table 1 lists the statistics of glaciers in different drainage systems. Clearly, most glacier resources were in the Hexi interior area, in both area and number of glaciers, followed by the Qaidam interior area and Datong River basin. In the sub-basins, the Shule River basin had the most plentiful glaciers, with an area and ice volume accounting for 31.91% and 35.11% of the corresponding glacier totals in the Qilian Mountains, respectively. The average area of glaciers was the largest and the ice volume of glaciers was the second largest in the Haltang River basin, although the number of glaciers was fewer than in the Beida, Heihe, and Dang River basins. The basin with the least glacier resources was the Bayan Gol River, which only had 10 glaciers covering an area of 2.20 km2. Although there were 375 glaciers with an area of 78.33 km2 in the Heihe River, the second largest inland river in China, the average glacier area was the least of the 11 sub-basins.
Table 1 Glacier statistics by drainage basin in the Qilian Mountains
Basin (Code) Sub-basin (Code) Number Area Average
area(km2)		 Volume
(%) (km2) (%) (km3) (%)
Datong
River (5J4)		 Datong River
(5J42)		 68 2.53 20.83 1.30 0.31 0.73 0.86
Hexi interior
area (5Y4)		 Shiyang River (5Y41) 97 3.61 39.94 2.50 0.41 1.55 1.83
Heihe River (5Y42) 375 13.97 78.33 4.90 0.21 2.39 2.83
Beida River (5Y43) 577 21.50 215.27 13.47 0.37 8.75 10.36
Shule River (5Y44) 660 24.59 509.87 31.91 0.77 29.66 35.11
Danghe River (5Y45) 318 11.85 203.77 12.75 0.64 10.08 11.93
Total 2027 75.52 1047.18 65.54 0.52 52.43 62.07
Qaidam
interior
area (5Y5)		 Buh River-Qinghai
Lake (5Y51)		 24 0.89 10.27 0.64 0.43 0.42 0.50
Haltang River (5Y56) 268 9.99 283.52 17.74 1.06 17.58 20.81
Har Lake (5Y57) 108 4.02 78.73 4.93 0.73 4.56 5.40
Iqe River-Tatalin
Gol River (5Y58)		 179 6.67 155.08 9.71 0.87 8.69 10.29
Bayan Gol River
(5Y59)		 10 0.37 2.20 0.14 0.22 0.06 0.07
Total 589 21.94 529.8 33.16 0.90 31.31 37.07
4.1.4 The distribution of glaciers in different provinces
Based on administrative divisions, glaciers in the Qilian Mountains were located within cities of Jiuquan, Zhangye, and Wuwei in Gansu Province and the autonomous prefectures of Haixi and Haibei in Qinghai Province (Table 2). There were 1492 glaciers with a total area of 760.96 km2 and an ice volume of 37.94 km3 in Gansu Province. The glaciers in the Qilian Mountains play a dominant role in Gansu province and their area and ice volume accounted for 94.99% and 95.09% of the corresponding provincial glacier totals (Liu et al., 2015). They were mostly distributed in Jiuquan and Zhangye. Although the number of glaciers in Zhangye was more than that in Jiuquan, the area and ice volume of glaciers located in the latter was two and three times the former, respectively. Wuwei only had 35 glaciers, with an area of 6.32 km2 and volume of 0.17 km3; it was the municipal level administrative unit with the least glacier resources in this region. Due to the inconsistency between the main ridge of the Qilian Mountains and the provincial boundary of Gansu and Qinghai, all the glacial melt-water on the northern side of the Qilian Mountains flows into rivers in Gansu Province; the downstream Datong River (Liancheng-Honggu segment) receives the meltwater from glaciers located in Qinghai Province. Therefore, there were 2363 glaciers with an area of 1351.53 km2 and ice volume of 70.74 km3, and the meltwater was available in Gansu Province.
Table 2 Glacier statistics by province in the Qilian Mountains
Province City/Autonomous
Prefecture		 Number Area Volume
(%) (km2) (%) (km3) (%)
Gansu Jiuquan 718 26.75 508.99 31.86 28.17 33.35
Zhangye 739 27.53 245.65 15.37 9.60 11.36
Wuwei 35 1.31 6.32 0.40 0.17 0.20
Total 1492 55.59 760.96 47.63 37.94 44.91
Qinghai Haixi 825 30.74 729.79 45.67 42.79 50.65
Haibei 367 13.67 107.06 6.70 3.75 4.44
Total 1192 44.41 836.85 52.37 46.54 55.09
Qinghai Province had 1192 glaciers with an area of 836.85 km2 and ice volume of 46.54 km3 in the Qilian Mountains. Although the number of glaciers in Haixi Mongol and Tibetan Autonomous Prefecture was twice that in the Haibei Tibetan Autonomous Prefecture, the area and ice volume of glaciers of the former were much greater than in the latter. Outside of the Qilian Mountains, glaciers in Qinghai Province are distributed in the Kunlun, Tanggula, and Bayan Har mountains. The number, area, and ice volume of glaciers in the Qilian Mountains accounted for 31.35%, 21.26%, and 16.94% of the corresponding glacier totals in Qinghai Province, respectively.

4.2 Glacier change in the Qilian Mountains in the past half-century

4.2.1 The change of number, area, and volume of glaciers
Statistics from the FCGI and SCGI datasets demonstrated that the area of glaciers in the Qilian Mountains decreased by 420.81 km2 (-20.88%) during the period 1956-2010. In total, 509 glaciers, with an area of 55.12 km2, completely disappeared; and 122 glaciers decreased in area from 241.35 km2 to 193.90 km2 and split into 262 smaller glaciers. In addition, there were 55 glaciers, with an area of 3.67 km2, that were not in the original FCGI dataset. Tian et al. (2014) suggested that the glacier areas in the Qilian Mountains were 2041.50 km2 and 1575.82 km2 in the 1990s and 2010s, respectively; the reduction in glacier area was 465.68 km2, or -22.81%. Some previous studies (e.g. Ding, 2002; Cao et al., 2010; Zhang et al., 2010, 2011; Bie et al., 2013) have indicated that glaciers retreated in the Qilian Mountains between the 1950s and 1990s. However, in the FCGI dataset, the glacier areas in the 1990s were >2014.96 km2, indicating that Tian et al. (2014) overestimated the glacier area change in the Qilian Mountains. In the past half-century, the glacier areas in Gansu and Qinghai decreased by 218.97 km2 (-22.39%) and 198.44 km2 (-19.17%), respectively.
As listed in Table 3, the ice volume of glaciers and their change were the largest using the empirical constants proposed in Grinsted (2013); the smallest values were calculated using the empirical constants in Radić and Hock (2010). The results from Liu et al. (2003) were in the middle. The average ice volume loss of glaciers based on the three methods was 21.63 km3 in the Qilian Mountains for the past 50 years. The rates of glacier ice volume loss were between -5.38 km3/10a and -5.67%/10a.
Table 3 Glacier volume changes in the Qilian Mountains based on three sets of empirical constants
Ice volume of glaciers in the FCGI (km3) Ice volume of glaciers in the SCGI (km3) Glacier volume change Method of glacier volume calculation Reference
km3 km3/10a %/10a
101.90 81.30 -20.60 -5.12 -5.65 V=0.0365A1.375 Radić and Hock (2010)
109.86 87.52 -22.34 -5.56 -5.69 V=0.0433A1.29 Grinsted (2013)
108.44 86.49 -21.95 -5.46 -5.66 V=0.04A1.35 Liu et al. (2003)
4.2.2 Characteristics of glacier change
An analysis of the relative area change compared to the initial glacier area indicated greater relative loss for smaller glaciers and greater absolute loss for larger glaciers in the Qilian Mountains (Figure 4). There were 999 glaciers in the size class <0.5 km2; their area loss percentage was >50% and accounted for 33.32% of the total number of glaciers. The area of glaciers in the size class <0.1 km2 decreased by 271.01 km2, which was 64.40% of the total area loss. Although the area loss of some glaciers in the size class ≥5.0 km2 exceeded 1.0 km2, their small quantities resulted in a percentage <5.0%. Hence, the glaciers in the <1.0 km2 size class overwhelmingly dominated, in both absolute area change and relative area change of the glaciers in the Qilian Mountains.
Figure 4 Percentage and area changes in glaciers in the Qilian Mountains from 1956 to 2010
Analysis of glacier hypsography showed that ice coverage above 5500 m remained almost unchanged while the highest absolute ice loss occurred around 4650 m (Figure 5). The percentage of glacier area change gradually decreased with increasing elevation. Alarmingly, glaciers below 4000 m disappeared. Although the area loss percentage of glaciers below 4250 m exceeded 80% of their initial area, the absolute area loss of glaciers between 4350 and 5100 m constituted the main body of loss, >15.0 km2 in each 50 m elevation band and 84.24% of the total area loss of glaciers.
Figure 5 Altitudinal characteristics of glacial changes in the Qilian Mountains from 1956 to 2010
The highest number and area of glaciers were oriented northward, followed by the northeast and northwest orientations (Figure 6). There were similar numbers of glaciers oriented south, southeast, and southwest, although glacier area with a southwest orientation was the greatest of these three. The number of glaciers oriented westward was more than that oriented eastward, but the area of the former was less than the latter. Statistical analysis indicated that glacier change was consistent with the size of glaciers in all orientations, except for the northwest. The largest and least absolute area losses of glaciers were in the north and south orientations, which were -210.34 km2 and -5.03 km2, respectively. From the perspective of relative area change, glaciers oriented eastward showed the largest decrease (-32.72%), followed by the southwest, southeast, west, and north orientations, which were between -29.91% and -23.73%. Notably, the area loss of glaciers with a northwest orientation was the least (-1.85 km2 and -0.95%), which was possibly related to the intensive westerly.
Figure 6 Orientation characteristics of glacial changes in the Qilian Mountains from 1956 to 2010
4.2.3 The regional differences in glacier change
The area change rates of glaciers in 11 drainage basins in the Qilian Mountains in the period 1956-2010 were clearly different (Figure 7). The most rapid decrease in glacier area occurred in the Shule River basin (5Y44) with a rate of -24.5 km2/10a, followed by the Beida River basin (5Y56) and Heihe River basin (5Y42), with rates of -21.7 km2/10a and -17.0 km2/10a, respectively. The Haltang River basin (5Y56), which has the second largest area of glaciers, had a rate of -9.7 km2/10a. The lowest rate, -0.2 km2/10a, was found in the Bayan Gol River basin (5Y59), which was likely due to the basin having the lowest area of glaciers.
Figure 7 Area changes of glaciers in different drainage basins in the Qilian Mountains from 1956 to 2010
A comparison of relative rates of glacier area change indicates that the Datong River basin (5J42) had the fastest decrease, -19.97%/10a, followed by the Heihe River basin (5Y42) and Shiyang River basin (5Y41), with relative rates of -15.67%/10a and -14.21%/10a, respectively. The relative rates were similar in the Beida River (5Y45), Buh River-Qinghai Lake (5Y51), and Bayan Gol River (5Y59) basins, between -9.49%/10a and -7.81%/10a. The relative rates of five basins located in the west of Har Lake were slower, with absolute values below 4.45%/10a. The Iqe River-Tatalin Gol River basin (5Y58) in the westernmost region had the lowest relative rate, -2.96%/10a. The average relative rate of glacier area change was -2.43%/degree in the longitudinal direction, which indicated an accelerating trend in glacier area recession from west to east in the Qilian Mountains.
Figure 8 Change in summer temperature, (a) June, (b) July, (c) August, and (d) annual precipitation in the Qilian Mountains from 1961 to 2010
Generally, glacier survival, development, and evolution are closely related to climate change (Duan et al., 2009; Xie and Liu, 2010; Wang et al., 2011). Temperature has a strong effect on glacier change over longer time scales and larger spatial extents, while precipitation influences glacier advance or retreat over short times and small scales (Gao et al., 2000). In the recent five decades, temperature has significantly increased in the Qilian Mountains. The average rate of temperature rise has been approximately 0.5°C/10a, but up to 1°C/10a, since the 1990s (Wang et al., 2009). Annual precipitation has also increased and has been mainly concentrated in the summer; however, changes in precipitation are also regionally varied (Wang et al., 2009; Zhang et al., 2014). The most recent studies have demonstrated that there has been a trend toward warm and dry in the spring, autumn, and winter and warm and wet in the summer along the Hexi Corridor (Wang et al., 2009; Lin et al., 2014). However, these studies have used data from sparsely distributed metrological stations in the Qilian Mountains; therefore, it has been difficult to examine regional differences in temperature and precipitation. In this study, the 0.5°×0.5° gridded dataset of monthly temperature and precipitation was adopted to analyze inter-decadal variability in the Qilian Mountains. There has been an obvious trend in temperature increases in summer, as shown in Figure 8. The rate of temperature rise generally exceeded 0.2°C/10a and the Heihe River witnessed the highest temperature rise in June, July, and August. The change in annual precipitation gradually increased from east to west. Except for the Datong River, the rate of precipitation increase was above zero; notably, precipitation increases were as high as 10.0-20.0 mm/10a in the western alpine regions around the Tulainan, Danghenan, and Tergun Daban mountains. It is likely that the larger recession of glaciers was due to increasing temperature in the central-eastern parts of the Qilian Mountains. The temperature also rose in the western region, but the increased precipitation mitigated glacier mass loss to some extent. However, the mass gain from increased precipitation could not fully balance the mass loss from rising temperatures, which resulted in the overall recession of glaciers in the Qilian Mountains.

5 Conclusions

This study presented the current status and characteristics of glacier change in the Qilian Mountains based on the FCGI and SCGI datasets. Some conclusions are drawn as follows:
(1) There were 3000 glaciers with an area of 2014.96 km2 in the revised FCGI dataset for the Qilian Mountains, which was more than previously published. A statistical analysis of the latest SCGI dataset demonstrated that there were 2684 glaciers with an area of 1597.81 ± 70.30 km2 and ice volume of ~84.48 km3 in the Qilian Mountains for the period 2005-2010. Glaciers in the Qilian Mountains were distributed in Gansu and Qinghai provinces, which respectively had 1492 glaciers covering 760.96 km2 with an ice volume of 37.94 km3 and 1192 glaciers covering 836.85 km2 with an ice volume of 46.54 km3.
(2) Glaciers in the <1.0 km2 size class accounted for the largest number of glaciers, while glaciers in the 1.0-5.0 km2 size classes accounted for the largest area of glaciers in the Qilian Mountains. The largest glacier was Laohugou Glacier No.12 with an area of 20.42 km2 in 2009. More than 58% of the total glacier area was located between 4800 and 5200 m in elevation. The average median elevation of glacier area was 4972.7 m, and gradually rose from 4483.8 to 5234.2 m from east to west.
(3) The Shule River basin included the largest area and ice volume of glaciers, 31.91% and 35.11% of the total corresponding values. The drainage basin with the least glacier resources was the Bayan Gol River, with a glacierized area of only 2.20 km2. The Heihe River, the second largest inland river in China, had the minimum average glacier area, 0.21 km2.
(4) The area and ice volume of glaciers in the Qilian Mountains decreased 420.81 km2 (-20.88%) and 21.63 km3 (-20.26%) from 1956 to 2010, respectively. The primary decline in glacier resources was in the <1.0 km2 glacier size class. Due to rapid glacial recession, glaciers below 4000 m completely disappeared and area loss of glaciers below 4500 m was up to 50% of the initial area. The glacier area reduction between 4350 and 5100 m accounted for 84.24% of the total area loss. The number and area of glaciers decreased in all directions. The area of glaciers decreased fastest for glaciers with eastern orientation and slowest for glaciers with northwestern orientation. The highest reduction in glacier area occurred for those oriented north, -210.34 km2.
(5) There was an obvious longitudinal zonality in glacier change in the Qilian Mountains, i.e., the glaciers were rapidly receding in the east but more slowly in the central and western regions. The difference of relative rate was largest between the east and west; for example, the relative rate of area loss was between -14.21%/10a and -19.97%/10a in the Datong River and Shiyang River basins, while it was only -2.96%/10a in the Iqe River-Tatalin Gol River basin. The main factor that most influenced glacier recession was warming temperature, although increased precipitation mitigated glacier mass loss to some extent.

The authors have declared that no competing interests exist.

References

Publishing order | Descend order by publishing year | Descend order by cited within
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Liu S, Sun W, Shen Y, et al., 2003. Glacier changes since the Little Ice Age maximum in the western Qilan Shan, northwest China, and consequences of glacier runoff for water supply.Journal of Glaciology, 49(164): 117-124.Based on aerial photographs, topographical maps and the Landsat-5 image data, we have analyzed fluctuations of glaciers in the western Qilian Shan, northwest China, from the Little Ice Age (LIA) to 1990. The areas and volumes of glaciers in the whole considered region decreased 15% and 18%, respectively, from the LIA maximum to 1956.This trend of glacier shrinkage continued and accelerated between 1956 and 1990. These latest decreases in area and volume were about 10% in 34 years. The recent shrinkage may be due either to a combination of higher temperatures and lower precipitation during the period 1956-66, or to continuous warming in the high glacierized mountains from 1956 to 1990. As a consequence, glacier runoff from ice wastage between 1956 and 1990 has increased river runoff by 6.2 km3 in the four river basins under consideration. Besides, the equilibrium-line altitude (ELA) rise estimated from the mean terminus retreat of small glaciers <1km long is 46 m, which corresponds to a 0.3 C increase of mean temperatures in warm seasons from the LIA to the 1950s.

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[13]
Liu S Y, Ding Y J, Li J, et al., 2006. Glaciers in response to recent climate warming in western China.Quaternary Sciences, 26(5): 762-771. (in Chinese)Glaciers in China are primarily located in the Qinghai-Xizang (Tibet) Plateau and surrounding high mountains. The China Glacier Inventory (CGI) indicates that there are over 46377 glaciers in Western China,accounting for 52 percent of the total area in Central Asia. Meteorological records indicate that air temperature in Western China has risen by 0.2 per decade,and the 1990s is likely the warmest decade of the millennium; similarly,most of Western China also has seen an increase in precipitation during the past 50 years,for example,precipitation increased by 18% during the last half of the last century in northwestern provinces. Using remote sensing and Geographical Information System (GIS) methods,we have monitored the changes over 5000 glaciers in the past 50 years. We conclude that 82.2% of all the monitored glaciers retreated,while the remaining glaciers were enhanced. It should be mentioned that the enhanced glaciers were not necessarily enhanced over the entire observational period; in the past two decades while regional climate warming has been much evident many of the once expanded glaciers started to retreat. As a whole,glaciers that have been monitored show a total area loss of 4.5% from the late 1950s to the late 1990s. Investigation on glacier changes over the past few decades reveal some regional differences,which is mainly attributed to different dynamical responses of glaciers with different sizes and physical properties along with climate changes of that region. For example,glaciers in central and northwestern parts of the Qinghai-Xizang Plateau were relatively stable,while those in mountains surrounding the Plateau experienced extensive wastage. It is concluded that strong warming and reduced precipitation are likely key drivers for the extensive reduction of ice cover in the eastern and southern parts of the Plateau. In contrast,recent cooling in the northwestern and central parts of the Plateau may partially explain the relatively stable condition of those glaciers. The modest warming trend and increase in precipitation in the southeastern part of the Plateau could account for the modest changes in glaciers there. Although precipitation has increased in Northwest China (Tianshan,Qilian Shan,Eastern Pamirs,and so on),the strong warming may be the principal factor driving glacier retreat although large glaciers with heavy debris covering their ablation areas may also contribute to the variations of ice extent in the region. Glacier recession is a key factor in the variability of water resources in the arid river systems of Northwest China. The recent increase in discharge of these rivers may be partially related to the increase in glacial runoff caused by loss of ice during glacier retreat. Although the glaciers that we (and others) have monitored account for only 10% of the total number and 24% of the total area of glaciers in China,our results may be extrapolated to infer glacier changes in various mountain regions of China.

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[14]
Liu S Y, Shen Y P, Sun W X, et al., 2002. Glacier variation since the maximum of the Little Ice Age in the western Qilian Mountains, Northwest China.Journal of Glaciology and Geocryology, 24(3): 227-233. (in Chinese)Variations of global land ice are of particular interest to global change scientists and governmental authorities, which concern the effects of glacier change on worldwide sea level change, glacial related disasters in mountainous regions and water resources in arid areas. For mountainous areas like high mountains and plateaus in Central Asian, glacier melt water plays an important role in the water supply for irrigation, industrial and common life, especially, in the drought years. In this paper, a comparative analysis is performed for glacier area variation since the maximum of the Little Ice Age (LIA) in the western Qilian Mountains, Northwest China. Glacier extents in the LIA maximum and in 1956 were derived from air photos and relevant photogrammetric maps. The extent in 1990 was extracted from Landsat TM image acquired in Sept. 1990, which was geometrically corrected by coregistering to the above-mentioned maps. It is found that total glacier area in four large river basins was in average 16.9% more than that in 1956 (Table 1). The satellite image of 1990 in the north part (Daxueshan Mountains) of the western Qilian Mountains demonstrated a glacier area decrease of 4.8% compared with that in 1956. An analysis has been performed for the data of glacier inventory of the western Qilian Mountains. The analysis shows that glacier area has close relationship to ice volume, as well as to glacier length. Thus, Glacier volume and length changes between the LIA and 1956 and between 1956 and 1990 can be calculated. Calculation shows that glacier volume and length changes were about 14.1% and 11 5% (relative to the situation in 1956) from the LIA to 1956. The calculation for the Daxueshan Mountains from 1956 to 1990 was extended to the western part of the Qilian Mountains by using the derived relations. It is revealed that glacier area and volume decreased by 10 3% and 9 3% during this period, which means that there was a much stronger recession of glaciers from 1956 to 1990, and correspondingly the rivers in this region have received an extra glacial runoff of about 50 10 8 m 3.

[15]
Liu S Y, Yao X J, Guo W Q, et al., 2015. The contemporary glaciers in China based on the Second Chinese Glacier Inventory.Acta Geographica Sinica, 70(1): 3-16. (in Chinese)The Second Chinese Glacier Inventory(SCGI) was compiled based on remote sensing images after 2004 including Landsat TM/ETM + and ASTER images,and the digital elevation models(DEMs) from SRTM.The SCGI shows that there are 48,571 glaciers with a total area of 5.18 104km2and ice volume of 4.3 103-4.7 103km3in China(including glaciers measured from 1:50,000 or 1:100,000 topographic maps made from the 1960 s to the 1980 s because of no high quality remote sensing images for the contemporary glacier inventories).The number of glaciers with the area below 0.5 km2 reaches 33,061 and accounts for the majority part(66.07%) of glaciers in China.Glaciers with areas between 1.0 km2 and 50.0 km2 are totaled as ~3.40 104km2(~2.65 103km3 in ice volume) and constitute the main part of glaciers in China.The Yengisogat Glacier(359.05 km2),located in the Shaksgam Valley,north slope of the Karakoram Mountain,is the largest glacier in China.The glaciers are spatially distributed in 14 mountains and plateaus in western China.The Kunlun Mountains has the largest number of glaciers in China,followed by Tianshan Mountains,Nyainq ntanglha Range,the Himalayas and Karakoram.Glaciers in the above five mountains account for 72.26% of the total glacier number in China,however,over 55% of the total area of glaciers and 59% of the total ice storage in China are concentrated in the Kunlun Mountains,Nyainq ntanglha Range and Tianshan Mountains.The number and area of glaciers in Karakoram Mountains are less than those in the Himalayas,but the volume of the former is more than that of the latter because the glaciers in the Karakoram are generally larger.Some 4/5 of the total area of glaciers in China is mainly distributed in an altitudinal band between 4500-6500 m a.s.l.with regional differences depending on the general elevations of various mountains.Analogously,there is an obvious difference of glaciers in basins.The first level basin having the most glaciers is the East Asia interior drainage area(5Y) which occupies ~40% of glaciers in China.The Yellow River basin(5J) has the fewest glaciers where only 164 with an area of 126.72 km2 are distributed.Xinjiang and Xizang autonomous regions are the two provincial units rich in glaciers,with ~9/10 of the total area and ice storage of glaciers in China.

[16]
Orelemans J, Anderson B, Hubbard A, et al., 1998. Modelling the response of glaciers to climate warming.Climate Dynamics, 14(4): 267-274.Dynamic ice-flow models for 12 glaciers and ice caps have been forced with various climate change scenarios. The volume of this sample spans three orders of magnitude. Six climate scenarios were considered: from 1990 onwards linear warming rates of 0.01, 0.02 and 0.0460K a -1 , with and without concurrent changes in precipitation. The models, calibrated against the historic record of glacier length where possible, were integrated until 2100. The differences in individual glacier responses are very large. No straightforward relationship between glacier size and fractional change of ice volume emerges for any given climate scenario. The hypsometry of individual glaciers and ice caps plays an important role in their response, thus making it difficult to generalize results. For a warming rate of 0.0460K a -1 , without increase in precipitation, results indicate that few glaciers would survive until 2100. On the other hand, if the warming rate were to be limited to 0.0160K a -1 with an increase in precipitation of 10% per degree warming, we predict that overall loss would be restricted to 10 to 20% of the 1990 volume.

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[17]
Paul F, Barry R G, Cogley J G, et al., 2010. Recommendations for the compilation of glacier inventory data from digital sources.Annals of Glaciology, 50(53): 119-126.Modern geoinformatic techniques allow the automated creation of detailed glacier inventory data from glacier outlines and digital terrain models (DTMs). Once glacier entities are defined and an appropriate DTM is available, several methods exist to derive the inventory data (e.g. minimum, maximum and mean elevation; mean slope and aspect) for each glacier from digital intersection of both datasets. Compared to the former manual methods, the new grid-based statistical calculations are very fast and reproducible. The major aim of this contribution is to help in standardizing the related calculations to enhance the integrity of the Global Land Ice Monitoring from Space (GLIMS) database. The recommendations were prepared by a working group and also contribute to the European SpaceAgency project GlobGlacier. The document follows the former UNESCO manual for the production of the World Glacier Inventory published in 1970, identifies the potential pitfalls, and describes the differences from the former methods of compilation. The online background material for this paper (see http://www.glims.org) contains example scripts for calculation of each parameter and will be updated when required.

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[18]
Racoviteanu A E, Paul F, Raup B, et al., 2009. Challenges and recommendations in mapping of glacier parameters from space: Results of the 2008 Global Land Ice Measurements from Space (GLIMS) workshop, Boulder, Colorado, USA.Annals of Glaciology, 50(53): 53-69.On 16鈥18 June 2008 the US National Snow and Ice Data Center held a GLIMS workshop inBoulder, CO, USA, focusing on formulating procedures and best practices for operational glaciermapping using satellite imagery. Despite the progress made in recent years, there still remain many caseswhere automatic delineation of glacier boundaries in satellite imagery is difficult, error prone or timeconsuming. This workshop identified six themes for consideration by focus groups: (1) mapping clean iceand lakes; (2) mapping ice divides; (3) mapping debris-covered glaciers; (4) assessing changes in glacier area and elevation through comparisons with older data; (5) digital elevation model (DEM) generation from satellite stereo pairs; and (6) accuracy and error analysis. Talks presented examples and work in progress for each of these topics, and focus groups worked on compiling a summary of availablealgorithms and procedures to address and avoid identified hurdles. Special emphasis was given to establishing standard protocols for glacier delineation and analysis, creating illustrated tutorials and providing source code for available methods. This paper summarizes the major results of the 2008 GLIMS workshop, with an emphasis on definitions, methods and recommendations for satellite data processing. While the list of proposed methods and recommendations is not comprehensive and is still a work inprogress, our goal here is to provide a starting point for the GLIMS regional centers as well as for the wider glaciological community in terms of documentation on possible pitfalls along with potential solutions.

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Radić V, Hock R, 2010. Regional and global volumes of glaciers derived from statistical upscaling of glacier inventory data.Journal of Geophysical Research, 115, F01010. doi: 10.1029/2009JF001373.1] Very few global-scale ice volume estimates are available for mountain glaciers and ice caps, although such estimates are crucial for any attempts to project their contribution to sea level rise in the future. We present a statistical method for deriving regional and global ice volumes from regional glacier area distributions and volume area scaling using glacier area data from 090804123,000 glaciers from a recently extended World Glacier Inventory. We compute glacier volumes and their sea level equivalent (SLE) for 19 glacierized regions containing all mountain glaciers and ice caps on Earth. On the basis of total glacierized area of 741 0103 103 00± 68 0103 103 km2, we estimate a total ice volume of 241 0103 103 00± 29 0103 103 km3, corresponding to 0.60 00± 0.07 m SLE, of which 32% is due to glaciers in Greenland and Antarctica apart from the ice sheets. However, our estimate is sensitive to assumptions on volume area scaling coefficients and glacier area distributions in the regions that are poorly inventoried, i.e., Antarctica, North America, Greenland, and Patagonia. This emphasizes the need for more volume observations, especially of large glaciers and a more complete World Glacier Inventory in order to reduce uncertainties and to arrive at firmer volume estimates for all mountain glaciers and ice caps.

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[20]
Shi Y F, 2000. Glaciers and Their Environments in China: The Present, Past and Future. Beijing: Science Press. (in Chinese)

[21]
Shi Y F, 2005. A Concise China Glacier Inventory. Shanghai: Shanghai Science Popular Press. (in Chinese)

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Shi Y F, Liu S Y, 2000. Pre-estimation for the response of China glaciers to global warming in the 21st century.Chinese Science Bulletin, 45(4): 434-438. (in Chinese)

[23]
Su Z, Zhao J D, Zheng B X, 2014. Distribution and features of the glaciers’ ELAs and the decrease of ELAs during the Last Glaciation in China.Journal of Glaciology and Geocryology, 36(1): 9-19. (in Chinese)The Qinghai-Xizang plateau and its bordering mountains is a special geographical unit in the lowand middle latitudes in the Northern Hemisphere,it has widest plateau and many peaks higher than 8 000 m a. s. l.This special geographical unit is a large center of modern glaciation,behind the polar regions( the Antarctica and the Greenland),making China to be a largest glacier country in the lowand middle latitudes on our planet. The main feature of the modern equilibrium line altitude( ELA) is latitudinal zonality,increasing about 150 m per degree from 49 N to 28 N. Moreover,the ELA appears asymmetric rings on the plateau. Based on the published literatures,the glaciers during the Last Glacial Maximum were estimated to be 50 104km2,8. 4 times larger than that of modern glaciers. According to the relationship between summer( June to August) average temperature and annual precipitation at ELA,the ELAs in western China( to the west of 105 E) during the LGM have been reconstructed,and the distribution and features of ELAs were similar to that of present. In the interior and the northwest of the plateau,the decrease of ELAs was less than 500 m,commonly,200 to 300 m,whereas,the decrease of ELAs was about 800 m on the southeastern margin of the plateau,with a maximal decrease of about1 000 to 1 200 m. The decrease of ELAs is about 500 m in the Tianshan and Altai ranges. However,there are no glaciers in eastern China( to the east of 105 E) at present. The glacial landforms that formed during the last glacial cycle have been preserved in several mountains,such as Helan Mountains,Taibai Mountains,Changbai Mountains and high mountains in Taiwan Island. The decrease of ELAs was 800 to 900 m,with an absolute value larger than that in western China. According to the reconstructed map of ELAs during last glaciation,and considering the palaeoclimate and palaeoenvironment,it is very clear that there were no glaciers developed on the mountains with peaks less than 2000 m in eastern China during Quaternary.

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[24]
Tian H, Yang T, Liu Q, 2014. Climate change and glacier area shrinkage in the Qilian Mountains, China, from 1956 to 2010.Annals of Glaciology, 55(66): 187-197.Glaciers in the Qilian mountains, located in the northeastern part of the Tibetan Plateau, constitute an important freshwater resource for downstream populations and natural systems. To enhance our understanding of the variability of the glaciers, temporally and spatially comprehensive information on them is needed. In this study, the glacier outlines of similar to 1990, similar to 2000 and similar to 2010 for the whole area were delineated in a semi-automated manner using band TM3/TM5 ratio images of Landsat ETM+ or TM scenes with the help of a merged ASTER GDEM/SRTM v4.1 digital elevation model. Combining our own results with those of previously published studies that span the period back to 1956, we found that the glacier area shrank by 30 +/- 8% from 1956 to 2010 and the shrinkage accelerated remarkably in the past two decades. The linear trends of annual air temperature and precipitation measured at weather stations within the glacierized areas were 0.03-0.05 C a(-1) (significant only after 2000) and 0.37-1.58 mm a(-1) (not significant) respectively from 1961 to 2010. Glaciers shrank mainly due to the increasing temperature. Glaciers in the Qilian mountains are very unlikely to have experienced positive mass balance over the past decade. Moreover, given the trend toward higher temperatures, the glaciers in this region will continue to shrink.

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[25]
Wang H J, Zhang B, Jin X H, et al., 2009. Spatio-temporal variations analysis of air temperature and precipitation in Qilian mountainous region based on GIS.Journal of Desert Research, 29(6): 1196-1202. (in Chinese)Based on the technology of ArcGIS,Kriging Interpolation Method and Surface Analyst,the monthly mean air temperature and precipitation data during 1960 through 2005 from 18 weather stations in Mt.Qilian region were analyzed.Their spatio-temporal variations are as follows: ①There was an obvious ascending trend of the air temperature in Mt.Qilian region from 1960 through 2005,with an increasing rate at about 0.5 ℃/10a;the ascending trend was the most obvious in the middle 1990's,and the increasing rate was more than 1 ℃/10a.②The change of air temperature in Mt.Qilian region kept well in phase with the change of air temperature in northwestern China.The distribution regimes of air temperature were same in summer and winter,but the temperature difference between north and south slope of the mountain was smaller in winter than that in summer.The monthly lapse rates of mean temperature differed seasonally,with low value in winter and high value in spring.③There was an ascending trend of precipitation in Mt.Qilian region from 1960 through 2005,and the precipitation distribution changed regionally and seasonally;precipitation reduced from south-east to north-west,and precipitation was less than 12 mm in winter and reached 230 mm in summer.

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[26]
Wang S J, Zhang M J, Li Z Q, et al., 2011. Response of glacier area variation to climate change in Chinese Tianshan Mountains in the past 50 years.Acta Geographica Sinica, 66(1): 38-46. (in Chinese)Based on the statistics of glacier area variation measured in Chinese Tianshan Mountains since 1960,the response of glacier area variation to climate change is discussed systematically.Results show that the total area of the glaciers has reduced by 11.5% in the past 50 years,which is a weighted percentage according to the glacier areas of 10 drainage areas divided by Glacier Inventory of China.The annual percentage of area changes(APAC) of glaciers in the Tianshan Mountains is 0.31%,after the standardization of the study period.According to the 14 meteorological stations in the Tianshan Mountains,both the temperature and precipitation display a marked increasing tendency from 1960 to 2009 with a rate of 0.34 oC·(10 a)-1 and 11 mm·(10 a)-1,respectively.The temperature in dry seasons(from November to March) increases rapidly with a rate of 0.46 oC·(10 a)-1,but the precipitation grows slowly at 2.3 mm·(10 a)-1;while the temperature in wet seasons(from April to October) grows with a rate of 0.25 oC·(10 a)-1,but the precipitation increases at 8.7 mm·(10 a)-1.

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[27]
Wang Y Z, Ren J W, Qin D H, et al., 2013. Regional glacier volume changes derived from satellite data: A case study in the Qilian Mountains.Journal of Glaciology and Geocryology, 35(3): 583-592. (in Chinese)Mass balance is the best measure of glacier health.Owing to laborious field work,mass balance measurements are restricted to a few glaciers,preventing the assessments of regional specific mass balance and glacier volume changes.Satellite elevation data provides feasible opportunities to monitor the glacier elevation changes,and then one can estimate the glacier volume changes easily.Here,the SRTM and ICESat data are used to derive the glacier volume changes in the Qilian Mountains.The results show that glaciers in the Qilian Mountains are losing mass in the early 21st century with a glacier thinning rate of(0.345±0.258) m·a-1((0.293±0.219) m w.e).It is estimated that the average mass loss over the entire study region is(534.2±399.5)×106 m3 w.e.a-1.Due to relative independence and large spatial seperation of various glacierized regions,small scale of glaciers and sparse distribution of ICESat ground tracks,the uncertainty might be high.

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[28]
Wang Z T, Liu C H, You G X, et al., 1981. Glacier Inventory of China I Qilian Mountains. Lanzhou: Lanzhou Institute of Glaciology and Cryopedology, CAS. (in Chinese)

[29]
Xie Z C, Feng Q H, Wang Xin, et al., 2005. Modeling the response of glacier system to climate warming: Taking glaciers in China as an example.Research of Soil and Water Conservation, 12(5): 77-82. (in Chinese)According to the Glacier Inventories of China,glaciers in China can be divided and sub-divided as 16 large,44 less large glacier systems based on the watershed.On the basis of the structure of the glacier system and the nature of the equilibrium line altitudes at the steady state,functional models of glacier system responding to climate warming were established,using Kotlyakov-Krenke's equation relating annual ablation of glacier and mean summer temperature and the representativity of glacier system's median size.The models are applied to the study of theresponse of glacier runoff to climatic change.The effect of decreasing air temperature due to rising of glaciers' ELA and reduction of glaciers area were considered in these models simultaneously.The modeling results under the climatic scenarios with temperature increasing rate of 0.02 K/a and 0.03 K/a indicate that,by the year of 2030,glacier runoff of China will reach climax level,then it will fall down,and get to the level of 20th's after the year of 2050.If climate continuously warming,the glacier area will continuously reduce,and by the year of 2030,2050,2100,the glacier area in China will averagely reduce for about 6%~9%,10%~15%,23.2% 34% respectively.

[30]
Xie Z C, Liu C H, 2010. Introduction to Glaciology. Shanghai: Shanghai Science Popular Press. (in Chinese)

[31]
Yan L L, Wang J, 2013. Study of extracting glacier information from remote sensing.Journal of Glaciology and Geocryology, 35(1): 110-118. (in Chinese)In this paper,remote sensing satellites,sensors used in monitoring glacier change and methods of extracting glacier information are summarized.Various approaches are evaluated synthetically.It is considered that the method of band ratio is the best among the conventional methods.The new methods of object-oriented classification and SAR interferometry have improved the accuracy of extracting glacier information to a certain extent.However,superglacial debris is still a difficulty in automatic recognition of glacier information.Automatic and semi-automatic methods have been developed for debris-covered glaciers.However,the methods are immature and out of universality.Obstacles of snow cover and superglacial debris and hard ground verification of glacier information derived from satellite images still need to overcome.Therefore,to develop more advanced and more sophisticated methods will be an important issue in glacier research.It is expected that rough set theory and waveform of ICESAT satellite will improve the accuracy of extracting glacier information.

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[32]
Yao X J, Liu S Y, Guo W Q, et al., 2012. Glacier change of Altay Mountain in China from 1960 to 2009: Based on the Second Glacier Inventory of China.Journal of Natural Resources, 27(10): 1734-1745. (in Chinese)Glacier change of Altay Mountain in China during the past 50 years was analyzed based on the outcome of Investigation of Chinese Glacier Resources and Their Changes and result of the First Glacier Inventory of China.The results showed that glaciers had been retreating in Altay Mountain in China from 1960 to 2009.The number of decreased glaciers reached 116,the area reduced 104.61 km2 and the volume loss was 6.19 km3.Compared with glacier change in other mountains in China,the annual average rate of glacier recession was the maximum in Altay Mountain where thus was the strongest region of glacier shrinkage.From the respect of glacier orientation,glaciers retreated in every direction.The maximum loss of glacier area occurred in north direction and the minimum appeared in west direction.The number and area of glaciers showed an obvious decrease tendency at altitudes of 2400-2600 m,2600-2800 m and 3000-3200 m.The most remarkable shrinkage of glaciers occurred at an altitude of 2600-2800 m.Glacier change had a regional difference.The number and area of glacier retreat decreased most in Burqin River watershed where the glaciers were concentrated.However,there was an inconsistency between number and area reduction of glaciers in other watersheds.The recession or disappearance of a large amount of small glaciers was the main cause of regional difference of glacier change.There was a close relation between glacier recession and climate change in Altay Mountain.The average temperature from May to September and precipitation from October to April in the next year from four meteorological stations in the study area both increased.The glacier recession in this region indicated that supplies to glaciers by increases in precipitation did not compensate for ablation rate increases caused by the dramatic temperature rise during the study period.

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[33]
You L Y, Yang J C, 2013. Geomorphology in China. Beijing: Science Press. (in Chinese)

[34]
Zhang H W, Lu A X, Wang L H, et al., 2010. Glacier change in the Lenglongling Mountain monitored by remote sensing.Remote Sensing Technology and Application, 2010, 25(5): 682-686. (in Chinese)

[35]
Zhang H W, Lu A X, Wang L H, et al., 2011. Glacier change in the Shulenan Mountain monitored by remote sensing.Journal of Glaciology and Geocryology, 33(1): 8-13. (in Chinese)Glaciers on the Tibetan Plateau play an important role in the earth's climate system.Regular survey of glacier change is almost impossible in most parts of the Tibetan Plateau.Remote sensing is a primary technique and becomes the only means in many places.GIS provides an efficient tool to analyze the status and the change of glaciers.In the paper,the Shulenan Mountain is selected as a test area.Glacier variation in the 1970s,1995,1999,2002 and 2006 were analyzed by means of satellite image and topographical map.The results indicate that the glacierized area had decreased about 5.8% from 1970 to 1995 and had decreased about 3.0% from 1995 to 1999.The glacierized area in 2002 had decreased about 1.7% compared with that in 1999,and the glacierized area in 2006 had decreased about 3.0% compared with that in 2002.Analyzing the annual mean temperature and precipitation of Tuole Station from 1957 to 2006,some evidence of glacier change are found.

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[36]
Zhang J T, He X J, Shangguan D H, et al., 2012. Impact of intensive glacier ablation on arid regions of northwest China and its countermeasure.Journal of Glaciology and Geocryology, 2012, 34(4): 848-854. (in Chinese)Arid Regions of Northwest China are most ecologically vulnerable regions and the core regions of national security and ecological security.The glaciers in the arid regions of Northwest China are called solid reservoirs.Melting water from glaciers is not only important water sources for the local development,but also the lifeblood of the local unique oasis economy.In the context of climate warming,the glaciers in arid regions of Northwest China ablate extremely and their number and size are decreasing.Intensive glacier ablation has seriously affected the pattern of regional water resources,the sustainable development of agriculture and the ecosystem stability,which challenge the existing water resources management system and disaster prevention measures.The development and management ideas should be changed,the capacity building of adaptation to the glacier retreat should be improved,and the technological research should be strengthened,in order to actively explore the adaptive countermeasures against the challenges of glacier retreat in Northwest China under global warming.

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[37]
Zhang L, Zhang Q, Feng J Y, et al., 2014. A study of atmospheric water cycle over the Qilian Mountains (I): Variation of annual water vapor transport.Journal of Glaciology and Geocryology, 36(5): 1079-1091. (in Chinese)In this paper,reanalysis data( NCEP I,NCEP II and ECM WF) w ere comparing w ith radiosonde data. NCEP I reanalysis data,together with observational meteorological data,were used to study the characteristics of water vapor transport over the Qilian Mountains for the period of 1960-2010. The reason of water vapor transport changing was analyzed. The relationships between summer precipitation and the East Asian Monsoon,the South Asian Monsoon,South China Sea Monsoon,zonal wind and subtropical anticyclone were also investigated. The results show that the precipitable water showed an obvious downward trend in the 1960 s,and then has basically remained stable from the 1970 s to present. As a whole,it is a decline trend. The remained water vapor has decreased and the net water balance has obviously gone down. Hereinto,the whole meridional water vapor transport,i. e.,north wind transport,has appeared positive value,resulting in positive contribution to net moisture budget. The whole zonal water vapor transport,i. e.,westerly transport,has appeared negative value,resulting in negative contribution to net moisture budget. Moreover,wind speed decreasing has resulted directly in water vapor transport decreasing and has further decreased net moisture budget. The change in w ind speed averaged from ground surface to 300 hPa height shows that zonal wind speed decreased by 13. 2% in the 1990 s as compared to that in the 1960 s,and meridional wind speed decreased by 10. 5%. The correlation coefficients between summer precipitation and summer monsoon indices show that the correlations are poor in western part,middle part and eastern part of the Qilian Mountains,which are mainly caused by the effects of special terrain,condition of circulation,researching season and time scale.

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[38]
Zhang M J, Wang S J, Li Z Q, et al., 2011. Variation of glacier area in China against the warming in the past 50 years.Acta Geographica Sinica, 66(9): 1155-1165. (in Chinese)According to the remote sensing records on glacier area in the typical regions of China,as well as the meteorological data of air temperature and precipitation at 139 stations and the 0 isotherm height at 28 stations,the variation of glacier area in China and its climatic background in the past 50 years was discussed.The initial glacier area calculated in this study was 23982 km 2 in the 1960s/1970s,but the present area was only 21893 km 2 in the 2000s.The area-weighted shrinking rate of glacier was 10.1%,and the temporal-interpolated annual percentage of area changes (APAC) of glacier was 0.3% a -1 since 1960.The high APAC was found at the Ili River Basin and the Junggar Interior Basin around the Tianshan Mountains,the Ertix River (a tributary of the Ob River) Basin around the Altay Mountains,the Hexi Interior Basin around the Qilian Mountains,etc.The retreat of glaciers was affected by climatic background,and the influence on glaciers of the slightly-increased precipitation is counteracted by the significant warming in summer.

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