Yao Tandongf Pu Jianchenf and Liu Shiyingf

*Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100029, China fCold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou Gansu 730000, China

55.1 Introduction

There are about 46,298 glaciers in High Asia, the total glacial area is about 59,406km2, and total glacial volume about 5590km3 (Table 55.1). These glaciers mainly concentrate around the Himalayas, Nyaiaqentanglha, Kunlun, Karakoram and Tienshan mountains. The glaciers in the Tibetan Plateau are the major component of the glaciers in High Asia. These glaciers extend north to the arid and desert regions, and become the main water resources in northwest China. Especially, the large glacier coverage around Tarim basin can supply about 137.7 x 108 m3 glacial meltwater to the lower reaches of the Tarim basin each summer. These glaciers extend south to the warmer, wetter forests and mainly concentrate around the Brahmaputra drainage basin, and form the largest mountain-glacier centre in High Asia. There are about 10,813 glaciers in the Brahmaputra drainage basin, the total glacial area is about 14,491 km2 and the glacial volume about 1293 km3.

Most of the inland rivers in norhwest China are supplied with glacial melt water (Table 55.2). According to the studies of Yang & Hu (1992) and Yang (1995), the annual glacial melt water runoff in China was about 56.4 km3 or 564 x 108 m3, which is close to the total annual runoff of the Yellow River, and is 2% of the total runoff in China, 10% of the total runoff in northwest China and 13% of the total runoff (4431 x 108 m3) of the four provinces in west China (Gansu, Qinghai, Xingjiang and Tibet). In fact, the glacial water resource is very important to the arid inland, mainly including Xingjiang, Qinghai and Gansu province in northwest China. According to the results of Yang (1995), the total glacial melt water runoff in northwest China was about 220.07 x 108m3.

Some rivers are dependent on glacial melt water in northwest China. The Tarim River is an example. There are 14,285 glaciers in the Tarim River basin, the total glacial area is 23,628.98km2, the glacial volume is 2669.435km3 and the average glacial depth is 113 m. According to a previous study (Yao et al., 2004), the total annual runoff of six tributaries of the Tarim River is 310 x 108 m3.

The runoff of the Tarim River supplied with the glacial melt water reached to about 50% in the past 40 yr.

Glaciers in High Asia are most sensitive to climatic change and fluctuate with climatic cooling and warming. Temperature rise since the termination of the Little Ice Age has had a great impact on glacial distribution, causing a decrease of glacial area and glacial volume (Yao & Shi, 1990). This is particularly the case for the temperate glaciers in the monsoon regions in High Asia. In the 1980s, most of the glaciers had retreated extensively because of climatic warming. Even some previously advanced glaciers had also shifted into retreat phase with rapid climatic warming. In the 1990s, glaciers had retreated more extensively, and the runoff of some rivers had increased largely with the glaciers melting (Shi, 2001; Yao et al., 2004).

From the 1950s, scientists have been studying the glacial fluctuation in High Asia. The study at the very beginning is pure field investigation and aerial photographs. Some long-term monitoring stations were established in the 1960s, 1970s and 1990s, which improved the continuous monitoring of glacial fluctuations. In the 1990s, remote sensing and GIS methods were used to study glacial fluctuation. These studies have provided the base for our discussion here.

55.2 Glacial retreat since the termination of the Little Ice Age

The Little Ice Age (LIA) was a typical cold period over High Asia (Yao et al., 1997). The LIA terminated about ad 1890 (Yao et al., 1996 ). Large-scale glacial retreat has started since then. The LIA in the High Asia can be divided into three cold stages, which appeared in the 15th century, the 17th century and the 19th century. The coldest stage appeared in the 15th century. The moraines corresponding to the LIA are different for different stages. The largest moraine is the one corresponding to the 15th century cold stage.

In High Asia, there are two types of glaciers: the temperate glaciers and the subpolar glaciers. These two types of glaciers are different in their response to climatic changes.

The Qilian Mountain is a region where subpolar glaciers developed. Some key areas were selected to study glacial fluctuations in the region. As shown in Table 55.3, glacial changes in different periods including the LIA, 1956, 1990 in the Big Snow Mountain in the Qilian Mountain are analysed and the magnitude of glacial fluctuations are calculated. In summary, the decrease of glacial area since the LIA to 1956 is about 4.7%, which is quite small compared with some other regions. However, the decrease from 1956 to 1990 is 4.8%, which is larger than the magnitude of decrease from the LIA to 1956 and indicates an accelerating decrease of glaciers.

Table 55.4 shows glacial area decrease from the LIA to 1956 in another key area in the Qilian Mountain. The magnitude of glacial fluctuation in the area is much larger compared with the Big Snow Mountain. As shown in Table 55.5, the magnitude of glacial fluctuation between the LIA and 1956 is also larger in the Shule River than in the Big Snow Mountain. Two facts are influencing the magnitude of the glacial fluctuations in the two regions: ice temperature and intensity of the monsoon. The Big Snow Mountain is in the western part of the Qilian Mountain. The ice temperature of glaciers is lower (close to polar glaciers) and less influenced by the monsoon. The ice temperature of glac

Table 55.1 Glaciers in different mountains in High Asia

Mountains

Number

Glacial area

Glacial

of glaciers

(km2)

volume (km3)

Altay

403

280

16

Sawuer Tienshan

21 9081

9236

17 1012

Table 55.2

Inland rivers

supplied by glaciers in High Asia

Parmir

1289

2696

248

Rivers

Number

Glacial area

Glacial volume

Karokoram

3454

6231

686

of glaciers

(km2)

(km3)

Kunlun

7694

12,266

1283

Alkin

235

275

16

Erqisi

403

289.29

16.40

Qilian

2815

1931

93

Zhunger

3412

2254.10

137.44

Qiangtang

958

1802

162

Inland rivers

2385

2048.16

143.71

Tanggula

1530

2213

184

Tarim

11,711

19,888.81

2313.30

Gandis

3538

1766

81

Tu-Ha

446

252.73

12.63

Nyainqentanglha

7080

10,701

1002

Hexi

2194

1334.75

61.55

Hdengduan

1725

1580

97

Quadam

1581

1865.05

128.53

Himalayas

6475

8412

709

Yellow

108

40.97

1.25

Total

46,298

59,406

5590

Total

22,240

27,973.86

2814.81

Table 55.3 Glacial changes during different periods in the Big Snow Mountain of the Qilian Mountains

Basin

Area in Little

Area in 1956

Area in 1990

Changes in

Changes in

Ice Age (LIA)

(km2)

(km2)

LIA-1956

1956-1990

(km2)

Area (km2)

Area (km2)

%

%

Chaganbulgas 34.61 32.02 28.98 -2.59 -8.1 -3.04 -9.5

Total/average 169.90 162.80 155.00 -7.59 -4.7 -7.82 -4.8

Chaganbulgas 34.61 32.02 28.98 -2.59 -8.1 -3.04 -9.5

Total/average 169.90 162.80 155.00 -7.59 -4.7 -7.82 -4.8

Table 55.4 Glacier-area fluctuations in the Shule River basin in the Qilian Mountains

Basin

Glacier area

Glacier area

Changes in

(%)

in 1956 (km2)

in LIA (km2)

LIA-1956 (km2)

Shule River 440.1 509.0 63.6 14.5

Danghe River 59.3 66.8 9.0 15.2

Beidahe River 66.9 66.9 14.0 20.9

Total/average 638.6 740.1 107.6 16.9

Shule River 440.1 509.0 63.6 14.5

Danghe River 59.3 66.8 9.0 15.2

Beidahe River 66.9 66.9 14.0 20.9

Total/average 638.6 740.1 107.6 16.9

iers in the Shule Rivers is higher (close to subpolar glaciers) and is influenced by the monsoon.

The magnitudes of glacial fluctuation of temperate glaciers in the intensive monsoon region are much greater. The temperate glaciers are in the Hengduan Mountains, the east section and on the south slope of the Himalayas, and the east section of the Nyainqentanglha Mountains in the southeast part of the Tibetan Plateau. Su & Shi (2002) studied the glacial fluctuation since the LIA. After investigation of 1139 glaciers from the Yulong, Gongga and Hengduan mountains, it was found that the total glacial area of the measured temperate glaciers has reduced by 30%. In the Yulong Mountains, the glacial area has reduced as much as 60% (He et al., 2003). The study indicates that there is an inverse relationship between glacier size and glacier area reduction. That is, the larger the glacier, the smaller the glacier area reduction, and vice versa.

Snowline in the temperate glacial region is a very sensitive indicator of glaciers to climatic changes. Through field investigation and careful comparison of lateral moraines in different periods, we obtained an estimate of snowline fluctuations in temperate glacier regions in High Asia. For example, the snowline of glaciers rose by 150-180 m on the east slope of the Yulong Mountains since the LIA, rose by 100-150 m in the Zayu River basin, and rose by 60-80 m in the Queershan Mountains.

55.3 Glacial retreat in recent years

In the 20th century, the glaciers in High Asia have retreated extensively as a result of climatic warming. The glacial changes can be divided into several stages, as follows:

Table 55.5 Glacier fluctuations in the Qilian Mountain in 1956-1990

Baidahe River 290.76 41.64 14.3

Shule River 589.64 49.56 8.4

Danghe River 259.74 25.04 9.6

Hala Lake 89.27 7.89 8.9

Total/average 1229.41 124.21 10.3

1 in the first half of the 20th century glaciers had advanced or shifted from advance to retreat;

2 between the 1950s and 1960s many glacial observations were started, and the glaciers in High Asia had begun to retreat extensively (Table 55.6)—according to previous studies (Zhang et al., 1981; Ren, 1988; Shi et al., 2002) about two-thirds of glaciers were retreating and 10% advancing, with the remainder being stable;

3 between the late 1960s and 1970s the glacial mass balance was positive, the snowline dropped and many glaciers advanced, with the proportion of advancing glaciers increasing and that of retreating glaciers decreasing;

4 in the 1980s glaciers again retreated extensively;

5 in the 1990s glacial retreat was more extensive than at any other period in the 20th century.

The glaciological expedition to the Tibetan Plateau in 1989 showed that the glaciers of the southeast Tibetan Plateau retreated extensively, and the Zepu Glacier and Kaqing Glacier were the most obvious examples of glacial retreat (Yao et al., 1991). Some glaciers, however, are still advancing. Detailed research of the Large Dongkemadi Glacier and the Small Dongkemadi Glacier in the Tanggula Mountains and the Meikuang Glacier in the Kunlun Mountains showed that these glaciers were still advancing. However, all these glaciers have shifted from advance to retreat during the 1990s. Now, with very few exceptions of glaciers still advancing, the glaciers in High Asia are retreating.

The glacial retreat since the 1990s has several main features as follows.

1 The magnitude of glacial retreat is increasing. Glacier No.1 in the Urumchi River basin in the Tianshan Mountains is an example. Glacier No.1 comprises two branches (east and west). The ice tongues of the east and west branches were joined together in 1962, but the junction was thinning continuously with the retreat of the two branches. In 1993, the two branches were totally separated from each other and the distance between the two branches reached to more than 100m in 2001. Figure 55.1 shows the retreat of the Glacier No.1 between the 1960s and 2000. Glacier No.1 retreated most extensively from the early 1960s to the early 1970s when the retreat rate reached to 6myr-1. The magnitude of glacial retreat decreased obviously during the mid-1970s and reached a minimum in the early 1980s, but increased again during the

Basin Area Area change %

Table 55.6 Proportions of advancing and retreating glaciers in High Asia at different periods

Time

Glaciers

Retreating

Advancing

Stable

Reference

glaciers (%)

glaciers (%)

glaciers (%)

1950-1970 1970-1980 1980-1990 1990 to present

He et al., 2003 Jing et al., 2002 He et al., 2003 Jing et al., 2002 Liu et al., 2003

This paper This paper

1950-1970 1970-1980 1980-1990 1990 to present

224 612 612

He et al., 2003 Jing et al., 2002 He et al., 2003 Jing et al., 2002 Liu et al., 2003

This paper This paper

Dongkemadi

Figure 55.1 Fluctuation of Glacier No.1 in the Urumqi River Basin.

Figure 55.1 Fluctuation of Glacier No.1 in the Urumqi River Basin.

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002

Figure 55.2 Fluctuations of the Larger Dongkemadi Glacier (a) and the Small Dongkemadi Glacier (b) in the Tanggula Mountains.

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002

Figure 55.2 Fluctuations of the Larger Dongkemadi Glacier (a) and the Small Dongkemadi Glacier (b) in the Tanggula Mountains.

late 1980s to the 1990s, with the retreat rate reaching a maximum of 6.5 myr-1 between 1990 and 1991.

2 Most of the advancing glaciers gradually shifted to retreat. The Large and Small Dongkemadi glaciers in the Tanggula Mountains are examples. Figure 55.2a & b show the process of the Large and Small Dongkemadi glaciers shifting from advance to retreat. These two glaciers were both advancing when they were first observed in 1991. The total area of the Large Dongkemadi Glacier is about 14.63 km2, and the Small Dongkemadi Glacier about 1.77 km2. Based on glaciological theory, there is a lag-time as a glacier responds to climatic change. The lag-time is dependent on glacial size: the larger the glacier, the longer the lag-time. Therefore, the time when the Small Dongkemadi Glacier began to shift from advance to retreat would have been earlier than the Large Dongkemadi Glacier. As shown in Fig. 55.2b, the Small Dongkemadi Glacier advanced about 4 m during the summer in 1992, and then shifted to retreat in 1993, with a retreat rate of only 0.2 m in that year. After 1993, the Small Dongkemadi Glacier kept retreating, and the retreat rate increased year by year and reached to 2.86 myr-1 in 2000. The Large Dongkemadi Glacier had advanced about 15.7m between 1989 and early 1994, and then shifted to retreat after the summer in 1994. The annual retreat of the Large Dongkemadi Glacier also increased continuously and the retreat rate reached to about 4.56 myr-1 in 2001.

3 At the highest peak of Mount Qomolangma there is also a record of the impact of global warming on the glacial process.

8850

8849

8848

0.12

0.00

8849

8848

1965

2000

1965

1970

1975

1990

1995

Figure 55.3 Height fluctuations at the top of Mount Qomolangma, where A is the lowering of surface height and B is the lowering rate in different periods.

1965

1965

1970

2000

1975

1990

1995

2000

Figure 55.3 Height fluctuations at the top of Mount Qomolangma, where A is the lowering of surface height and B is the lowering rate in different periods.

According to Ren et al. (1998), climatic warming caused glacial retreat in Mount Qomolongma. Furthermore, evidence of the impact of climatic warming on glaciers was also found at the top of Mount Qomolangma. According to the observation of Chen et al. (2001), the surface height of the snow and ice at the peak of Mount Qomolangma has lowered since 1966. The observation data show a variable lowering rate over the past several decades. As shown in Fig. 55.3A, the surface height at the top of Mount Qomolangma lowered by a total of about 1.3 m (from 8849.75 m to 8848.45 m) between 1966 and 1999. The annual fluctuations of the surface height of snow and ice (in Fig. 55.3B) are as follows: the rate of lowering was very fast between 1966 and 1975, with the annual lowering rate reaching about 0.1m; the rate of lowering slowed between 1975 and 1992 to only about 0.01myr-1, one-tenth of that between 1966 and 1975; it then increased again between 1992 and 1998 to a rate of 0.1 myr-1, with the annual lowering rate reaching a maximum of 0.13 myr-1 between 1998 and 1999. Such a large lowering of surface height in so short a time confirms that the reduction in height cannot be caused by lithospheric movement, and can be explained only by glacial response to climatic change. Strictly speaking, glacial retreat cannot cause the lowering of glacier surface height at 8848 m a.s.l, but the process of glacial ice formation can induce lowering of the glacier surface height. The depth of snow and ice at the top of Mount Qomolangma is still unclear. A maximum depth of 2.5 m was observed by the Italy Mountaineering Team using a stick, but the true depth of snow and ice cannot be obtained with this method. However, the snow and ice depth at the top of Mount Qomolangma should be deeper than 2.5 m. Prior to global warming, the snow-ice formation process at this altitude is one of very slow densification under gravity. It is similar to that of the Antarctic and Arctic regions. Following global warming, the snow-ice formation process will accelerate as a result of temperature increase, which will cause rapid lowering of the glacier surface height. In fact, the rate of lowering of surface height since 1992 at the top of Mount Qomolangma corresponds to a period of rapid climate warming. 4 The pattern of glacial retreat is different in different regions according to many studies (Su et al., 1996, 1999; Wang & Liu, 2001; Pu et al., 2001; Lu et al., 2002; Jing et al., 2002; Chen et al., 1996; Liu et al., 2000, 2002). Figure 55.4A indicates the observations of the actual retreat of typical glaciers in different regions. These observations show that glacial retreat was extensive in the Karakorum Mountains and southeast Tibetan Plateau, with the annual retreat of Poshu Glacier in the Karakorum Mountains reaching about 50 m. Glacial retreat in the innner Tibetan Plateau was less, at no more than 10myr-1. For example, the annual retreat rates of the Puruogangri Glacier and the Malan Ice Cap in the Tibetan Plateau were within 10 myr-1.

At the plateau scale, the magnitude of glacial retreat is smaller inland and larger at the margin. Figure 55.4B indicates that the magnitude of glacial retreat was large in the southeast Tibetan Plateau and Karakorum Mountains (e.g. the annual glacial retreat in the Karakorum Mountains reached 30 m and 40 m in the southeast Tibetan Plateau), whereas the annual glacial retreat in the Kunlun Mountains and Tanggula Mountains (located in the central Tibetan Plateau) was smaller at no more than 10 m. This kind of regional difference of glacial retreat forms an elliptical shape of the glacial retreat in recent years on the Tibetan Plateau, and the distribution feature was similar to that of the glacial

1-AltayMt.

2-Tianshan Mt.

3-KarakoramMt.

4-Qilian Mt.

5-Himalayas Mt

6-Tanggula Mt.

7-Gangdise Mt.

8-Kunlun Mt.

9-Nyainqcnumglha Mt

10-Hengduan Mt.

11-Qiangtang Plat

1-GlacierNo.

2-Basu Glacier

3-Qiyi Glacier

4-XidatanGla.

5-Dasuopu Gla.

6-Kangwure Gla.

1-GlacierNo.

2-Basu Glacier

3-Qiyi Glacier

4-XidatanGla.

5-Dasuopu Gla.

6-Kangwure Gla.

7-Qiangyong Glacier

8-Large Dongkemadi Glacier

9-Small Dongkemadi Glacier

10-Rongbuk Glacier

11-Hailuogou Glacier

12-Puruogangri Glacier

13-Malan Glacier

Observation sites

Figure 55.4 Regional features of glacial retreat in High Asia, where (A) shows the annual retreat rate of all the glaciers in a region and (B) shows the annual retreat rate of glacial length observed in different regions.

shrinkages from the maximum of the Little Ice Age to present (Fig. 55.5). The central part of the elliptical regional distribution is located in the Tanggula Mountains, Kunlun Mountains and Qiangtang Plateau in the inner Tibetan Plateau, which record minimum glacial retreat. The glacial retreat increases from inland areas to the margin of the Tibetan Plateau, and reaches a maximum in the southeast Tibetan Plateau and Karakorum Mountains.

55.4 Negative glacial mass balance causes glacial retreat in High Asia

Mass balance is the algebraic sum of glacial mass increase (precipitation on the glacier) and glacial mass loss (glacier melting) in the glacier system. A positive value means a positive glacial mass balance and vice versa. The general glacial retreat pattern in High Asia is closely related to the strong negative glacial mass balance of recent years.

Continuous observation sites of glacial mass balance in High Asia include Glacier No.1 in the Urumqi River basin (1956— 2001), Small Dongkemali Glacier in the Tanggula Mountains (1990-2001) and Meikuang Glacier (1990-2001) in the Kunlun Mountains. Figure 55.6 shows mass-balance fluctuations of these glaciers in recent years. Obviously, the mass balance of these glaciers cannot reflect the pattern of the whole of High Asia, but studying the characteristics of these fluctuations can help us understand the retreat trends for the whole of High Asia.

There are several different features in the mass balance of these glaciers. Glacier retreat is most extensive in the Tianshan Mountains where the mass balance was strongly negative all the time.

The advancing glaciers in the central and north Tibetan Plateau shifted to a retreat phase recently, and their mass balances changed from positive to negative. From Fig. 55.6, the mass balance of Glacier No.1 in the Tianshan Mountains was not only strongly negative all the time, but also its absolute value was the largest among the three glaciers. The mass balance of the Meikuang Glacier was very similar to that of the Small Dongkemadi Glacier, being mostly positive before the 1990s, which coincides with advances of the two glaciers before the 1990s. The mass balances of the Small Dongkemadi Glacier in the Tanggula Mountains and Meikuang Glacier started becoming negative in the mid-1990s. It was a strong signal of general retreat of glaciers in High Asia.

As mentioned above, negative mass balance is the direct cause of glacial retreat in High Asia. Precipitation in most parts of High Asia is increasing, providing the potential for a shift to a positive mass balance. However, many studies have shown obvious temperature rises in High Asia. Therefore, the key cause of general glacial retreat in High Asia is temperature rise due to global warming.

55.5 Conclusions

Glaciers in High Asia are retreating extensively as a result of global warming. The glacial retreat can be divided into several stages during the 20th century. Glaciers advanced, or shifted from an advancing to a stable state, during the early half of the 20th century. From the 1950s to the late 1960s the glaciers in High Asia retreated on a large scale, the retreat slowed down in the 1970s, and became extensive again in the 1980s. The glacial retreat in the

I Kilo 850

212.5 425

I Kilo 850

Legend

-59 - ■

45.9

n

-45.9

- -43.9

'0" °0'

H

-43.9

- -42.3

M

-42.3

- -41.5

4

M

-41.5

- -40

M

-40 - ■

35.9

M

-35.9

- -31.4

H

-31.4

- -28.6

-28.6

- -24.8

'0"

■■

-24.8

- -19.8

H

-19.8

- -13.4

CO

H

-13.4

- -9.1

H

-9.1 -

-6.4

M

-6.4 -

-3.5

-3.5 -

0

'0"

°0'

CO

Figure 55.5 Regional features of the glacial fluctuations in High Asia. (See www.blackwellpublishing.com/knight for colour version.)

Figure 55.6 Glacial mass balances of some glaciers in High Asia.

Figure 55.6 Glacial mass balances of some glaciers in High Asia.

1990s is the most extensive. During this period, most glaciers that were advancing are now retreating. The glacial retreat was most extensive on the southeast Tibetan Plateau and in the Karakorum Mountains and least extensive in the central Tibetan Plateau.

Glacial retreat in High Asia is due to negative glacial mass balance as a result of higher temperatures caused by global warming. The long-term data of several glaciers show that the positive mass balance recorded between the end of the 1960s and the late 1970s caused the glacial snowline to fall. At that time, the ratio of advancing glaciers increased and that of retreating glaciers decreased. In the 1980s, glacial mass balance became more negative. In the 1990s, the glaciers with negative mass balance became the most negative and a few glaciers with positive mass balance previously also shifted to a negative balance. The glacial retreat in the 1990s was the most extensive compared with any other period during the 20th century. It is concluded that the cause of the most recent glacial fluctuation in High Asia is increased temperatures due to global warming.

Acknowledgements

This study has been supported by the Innovation Group Fund of the National Natural Science Foundation of China (Grant No. 40121101), the Project KZCX2-SW-339 and the Project KZCX2-SW-118 of the Chinese Academy of Sciences.

Glacier composition, mechanics and dynamics

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