Environ Geol (2008) 56:59–68 DOI 10.1007/s00254-007-1139-2

ORIGINAL ARTICLE

Glacier change and glacier runoff variation in the Tuotuo River basin, the source region of Yangtze River in western China Yong Zhang Æ Shiyin Liu Æ Junli Xu Æ Donghui Shangguan

Received: 17 July 2007 / Accepted: 13 November 2007 / Published online: 30 November 2007 Ó Springer-Verlag 2007

Abstract Glaciers in the Tuotuo River basin, western China, have been monitored in recent decades by applying topographical maps and high-resolution satellite images. Results indicate that most of glaciers in the Tuotuo River basin have retreated in the period from 1968/1971 to 2001/ 2002, and their shrinkage area is 3.2% of the total area in the late 1960s. To assess the influence of glacier runoff on river runoff, a modified degree–day model including potential clear-sky direct solar radiation has been applied to the glaciated regions of the river basin over the period 1961–2004. It was found that glacier runoff has increased in the last 44 years, especially in the 1990s when a twothirds increase in river runoff was derived from the increase in glacier runoff caused by loss of ice mass in the entire Tuotuo River basin. Keywords Tuotuo River basin
Glacier change
Glacier runoff
River runoff
Climate change
Water resources

Y. Zhang (&)
S. Liu
J. Xu
D. Shangguan State Key Laboratory of Cryospheric Science, Cold and Arid Regions Environmental and Engineering Research Institute (CAREERI), Chinese Academy of Sciences (CAS), Lanzhou 730000, People’s Republic of China e-mail: [email protected] Y. Zhang Graduate School of Environmental Studies, Nagoya University, Nagoya 464-8601, Japan

Introduction Glaciers are characteristic features of mountain environments in western China, and account for 52% of the total area of all glaciers in High Mountain Asia (Wu and Li 2004). These glaciers are valuable natural reservoirs of water and have a large effect on the drainage characteristics of alpine catchments. It is well-known that water resources are a key factor in the sustainable development of human activities and for the ecological environment in the arid/semiarid regions of western China, where these glaciers have a substantial influence on the local water cycle by temporarily storing water as snow and ice on many different time-scales (Yao et al. 2004), as they do in many other parts of the world (Jansson et al. 2003). Scientific communities and sectors of water resources management have recently gradually recognized the strong influence of glaciers on catchment runoff quantity and distribution. Such influence occurs not only in the glaciated catchment but also in adjacent lowlands far beyond the limits of mountain ranges (Yao et al. 2004; Shi et al. 2005). Since the beginning of the twentieth century, mountain glaciers have generally experienced worldwide retreat and thinning in response to a *0.74°C increase in global mean surface temperature (Lemke et al. 2007; Trenberth et al. 2007). General circulation models (GCMs) project enhanced global warming in the coming decades, which is very likely to accelerate current glacier decline (Meehl et al. 2007). Consequently, additional fresh water is expected to be released from glacier storage because of the worldwide retreat of glaciers, thus further modifying current streamflow regimes (Jansson et al. 2003; Meehl et al. 2007). Data from meteorological stations have shown that the source region of the Yangtze River, located in the center

123

60

of the Tibetan Plateau, is the area most sensitive to global warming and with the largest warming trend (Yang et al. 2004; Zhang et al. 2006a; Kang et al. 2007), not excepting the Tuotuo River basin as the headstream of the Yangtze River (Zhang et al. 2006b; Kang et al. 2007). The current ice core d18O record of Mt Geladandong located in the Tuotuo River basin (Fig. 1) showed that the rate of warming since the 1990s (1.1°C/10 years) is approximately twice that since the 1970s (0.5°C/10 years), reflecting accelerated warming and a more sensitive response to global warming in this region (Kang et al. 2007). Under the ongoing accelerated warming, a key scientific issue of great concern for us is how variation in glaciers and glacier runoff affect water resources and the ecological environment in the Tuotuo River basin and/or

Fig. 1 Location of the Tuotuo River basin in the source region of Yangtze River (SRYR) and the distribution of existing glaciers

123

Environ Geol (2008) 56:59–68

the source region of Yangtze River. Although glacier changes of Mt Geladandong in this region have been investigated (e.g. Lu et al. 2002; Ye et al. 2006a), little is known about the whole variation characteristics of glaciers and glacier runoff in the entire Tuotuo River basin during recent decades. In this paper, therefore, the main purpose is twofold. First, the total feature of glacier change in the Tuotuo River basin is analyzed for the period from 1968/1971 to 2001/2002 by using the topographical maps and highresolution satellite images. Second, glacier runoff in the river basin is simulated for the period 1961–2004 by using a modified degree–day model including potential clearsky direct solar radiation and then analyzing the variation characteristics of glacier runoff and their possible effect

Environ Geol (2008) 56:59–68

on water resources. Additionally, another aim of this paper is to test the applicability of the modified degree– day model to the Tuotuo River basin where cold-type glaciers are dominant (Huang 1990). Such work is a necessary first step toward predicting the response of glacier runoff to future climate change in this poorly understood region.

Study area The Tuotuo River basin is located in the west of the source region of Yangtze River, western China (Fig. 1). It is one of the primary glacier regions in the source region of Yangtze River (Shi et al. 2005). According to the Chinese glacier inventory (CGI) for the Yangtze River, there are 92 glaciers within the entire Tuotuo River basin (Shi et al. 2005); these glaciers have a total area and volume of 389.09 km2 and 42.15 km3, respectively, which account for 12.1, 30.5, and 42% of the total number, area, and volume, respectively, of all glaciers in the source region of Yangtze River (Shi et al. 2005). Of seven glaciers larger than 30 km2 in the Yangtze River region, there are four glaciers in the Tuotuo River basin—the Qiesumeiqu Glacier, the southern and northern Jianggudiru Glaciers, and Glacier 5K451F69 (Fig. 1). As indicated in Fig. 2, glaciers less than 2.0 km are dominant, accounting for 66.3% of the total number of all glaciers in the river basin, but their area and volume only account for 12.5 and 5.1%, respectively, of the total values in the river basin. On the other hand, there are only 16 glaciers greater than 5 km, and their area and volume account for 74.8 and 84.1%, respectively, of the total values in the river basin.

61

Glacier changes during recent decades Data and methods Topographical maps (1:100,000) based on aerial photographs acquired during 1968–1971, Landsat 7 Enhanced Thematic Mapper Plus (ETM+) images obtained during 2001–2002 (Table 1), and a digital elevation model (DEM) with 90 m resolution developed in 1981 were used in this study. Note that there is almost no cloud cover and snow cover in these Landsat ETM+ images. The methods used for image processing and glacier boundary extraction are the same as widely used by many different authors in western China (e.g. Lu et al. 2002; Shangguan et al. 2004, 2006; Liu et al. 2006a, b; Ye et al. 2006a, b). All satellite images were geometrically corrected using the 1:100,000 topographical maps and projected into the world geodetic system 1984 (WGS84) and the universal transverse mercator (UTM) coordinate system. All the corrected images were then orthorectified with the Orthobase Generic Pushbroom package using the 90 m resolution DEM in 1981 and the 1:100,000 topographical maps, in order to remove the shadow effect of high mountainous ridges. The corrected Landsat ETM+ images with 30 m resolution including bands 5, 4, and 3 were combined into false color composite images, which are all merged with band 8, furnishing false color composite images with 15 m resolution. Comparison of the different methods used for image classification to extract glacier borders (Paul 2000; Paul et al. 2002) revealed that the TM3/TM5 ratio with a threshold larger than 2.1 gave the best result in such work. This method is mainly based on glacier ice with very low reflectance in the middle infrared (Rott 1994; Paul 2002). Hence, in this work glacier boundaries on the corrected images were extracted by the ratio TM3/TM5 with a threshold larger than 2.1. Because of the limitations of the method employed (Paul et al. 2002), misidentification is frequent. Therefore, visual interpretation is applied combined with the DEM and multispectral satellite images (Paul et al. 2004). Commercial geographic information system (GIS) software is applied to such identification and vectorization of glacier boundaries. Glacier boundaries for the period 1968–1971 are vectorized from the topographical maps modified with careful reference to the information from the CGI. The Table 1 Landsat ETM+ used in this work Image Landsat ETM+

Fig. 2 Frequency of number, area, and volume of glaciers, according to length class, in the Tuotuo River basin

Path/row

Data

RMSE (m)

138/36

3 October 2001

12.3

138/37

15 May 2002

13.5

139/36

24 September 2001

15.6

123

62

Environ Geol (2008) 56:59–68

attribute data consisting of more than 27 elements for a glacier vectorized from such maps are obtained from the CGI, with relevant corrections for area, length, etc., based on this vectorization. Glacier changes during the time-span are then obtained by applying the overlay function of the GIS software. In addition, 20 independent verification points (Dwyer 1995; Li et al. 1998) were selected from each image and the corresponding topographical map in order to check the accuracy of co-registration. The result showed that the residual root-mean-square error (RMSE) of all images was less than 15.6 m (Table 1).

Glacier changes Over the period 1968/1971–2001/2002, although some glaciers were advancing in the Tuotuo River basin, most were retreating (accounting for 72% of the total number of all glaciers in the river basin). Comparison of the amount of glacier advance with the amount of glacier retreat revealed a net decrease in total area of 3.2% during 1968–1971. It can be seen that glacier retreat is the dominant phenomenon in the Tuotuo River basin, which agrees well with the temperature increase recorded in the Geladandong ice core (Kang et al. 2007). With the marked increase in air temperature since the early 1990s (Zhang et al. 2006b; Kang et al. 2007), glaciers show a rapid retreat in the Tuotuo River basin. For example, these glaciers in Mt Geladandong (Fig. 1) experienced a retreat in area at a mean rate of 0.68 km2/year over the period 1969–1976, 0.96 km2/year over the period 1977–1992, and 2.24 km2/year over the period 1993–2002 (Ye et al. 2006a). In terms of glacier area, all glaciers in the Tuotuo River basin are divided into six area classes: B0.2, 0.2–0.5, 0.5– 1.0, 1.0–5.0, 5.0–10.0, and C10.0 km2. As shown in Fig. 3, in the same way as for relative changes of glaciers in different area classes, small glaciers generally display a higher percentage area reduction than large glaciers, and thus greater sensitivity to climate change. Among the six area classes, area reductions of glaciers of B0.2 and 5.0– 10.0 km2 are the largest and smallest, respectively; this accounts for 55.6 and 1.3%, respectively, of the total area in the corresponding area class (Fig. 3). On the other hand, the contribution of area reduction of large glaciers to the total area reduction of all glaciers in the river basin is larger than that of small glaciers. Although the relative changes of glaciers C10.0 km2 is less pronounced, their area reduction contributes up to 57.7% of the total area reduction of all glaciers in the river basin (Fig. 3). Table 2 shows the area changes of glaciers greater than 25.0 km2 in the Tuotuo River basin for the period 1968/

123

Fig. 3 Area changes of different area classes in the Tuotuo River basin for the period 1968/1971–2001/2002 Table 2 Area data for glaciers greater than 25.0 km2 in the Tuotuo River basin over the period 1968/1971–2001/2002 Glacier

Area in 1968/1971 (km2)

Area change (km2)

Percentage (%)

Southern Jianggudiru

33.30

-0.70

-2.10

Northern Jianggudiru

27.53

-0.91

-3.30

Qiesumeiqu

54.04

-1.31

-2.42

5K451F69

30.37

-2.66

-8.76

1971–2001/2002, which indicates that the four glaciers all display a retreating trend during the period studied. Among the four glaciers, the shrinkage trend is largest for Glacier 5K451F69, which decreases by approximately 8.8% compared with that during 1968–1971 (Table 2). Additionally, Southern Jianggudiru Glacier, the second largest glacier in the river basin, has experienced a very rapid retreat in length at a mean rate of 41.5 m/year for the period 1969–2000 (Lu et al. 2002), and its area decreased by approximately 2.1% compared with that in 1969. In contrast, approximately 6.5% of the total number of glaciers in the river basin was advancing, for example, Glacier 5K451F12 experienced a significant rapid advance in length at a mean rate of 21.9 m/year for the period 1969–2000 (Lu et al. 2002), and its area increased by approximately 8.5%. Previous study has reported that Glacier 5K451F12 may be a surging glacier, which may be independent of the current climate change in this region (Shi et al. 2005). Nevertheless, because of the scarcity of long-term observation data in the glaciated regions of the Tuotuo River basin, the reason for the advance of Glacier 5K451F12 is uncertain, and warrants further study.

Environ Geol (2008) 56:59–68

63

Variation in glacier runoff during recent decades With ongoing accelerated warming (Kang et al. 2007) and glacier retreat, additional fresh water is expected to be released from glacier storage thus further modifying current river runoff of the Tuotuo River, which is a glacier-fed river (Yang 1991; Xie et al. 2003). Therefore, in this section, glacier runoff is simulated over a period of 44 years (1961–2004), and the possible effect of glacier runoff on river runoff in the Tuotuo River basin is then analyzed. Herein, daily mean values of temperature and precipitation, above-mentioned glacier-change data, and annual discharge of river runoff are used. The temperature and precipitation time series are obtained from the two national meteorological stations, which are Tuotuohe (33°570 N, 92°370 E, 4,533 m a.s.l.) and Wudaoliang (35°130 N, 93°050 E, 4,614 m a.s.l.), respectively (Fig. 1). Annual discharge of the Tuotuo River was obtained from the Tuotuohe station (33°570 N, 92°370 E, 4,533 m a.s.l.) for the period 1961–2000 (Fig. 1).

Method Glacier runoff simulation is carried out in daily time steps through a modified degree–day model including potential clear-sky direct solar radiation. The glaciated region of the Tuotuo River basin is represented as a set of spatial units, each of which is assumed to have homogenous hydrological behavior. The glaciated regions in the river basin can be divided into a set of elevation bands at intervals of 100 m, and the glacier area of each elevation band is derived from the 90 m DEM. For each elevation band, the temperature and precipitation time series are interpolated from the neighboring meteorological stations. For the temperature time series, a constant lapse rate is applied to the temperature series measured at the closest meteorological station, which is fixed to -0.50°C per 100 m of altitude increase (Ding et al. 1992; Li et al. 2003). Previous studies have suggested that precipitation increases linearly with elevation in the glaciated catchments on the north slope of Tanggula Mountains (Ding et al. 1992; Yao 2002). Therefore, the precipitation increase with altitude is set to a fixed percentage of the amount observed at the meteorological station located near the glaciated regions studied, which is set to 11.2% per 100 m (Yao 2002). For each elevation band, the aggregation state of precipitation is determined according to a simple temperature threshold (WMO 1986; Fujita and Ageta 2000; Zhang et al. 2006c, 2007). That is given by: Psnow ¼ Ptot ; Pliq ¼ 0 ; Psnow ¼ 0 ; Pliq ¼ Ptot ;

T  T0 T [ T0

ð1Þ

where Ptot is the total precipitation on a given day, Psnow the solid and Pliq the liquid precipitation, T is the mean daily air temperature, and T0 is the threshold temperature. Estimation of the aggregation state of precipitation is essential for modeling of the glacier runoff process. In this study, the threshold temperature is set to 2.0°C (e.g. Ye et al. 2004; Zhang et al. 2006c; Yang et al. 2006). A mixture of snow and rain is assumed for a transition zone ranging from 1 K above and below the threshold temperature. Within this temperature range, the snow and rain percentages of total precipitation are obtained from linear interpolation. Redistribution of the original snowfall by wind transport or avalanches is not considered. Glacier melt M in the ith elevation band is computed by use of a modified degree–day model including potential clear-sky direct solar radiation at the surface, which overcomes the shortcomings of the classical degree–day model with regard to temporal resolution and the spatial variability of melt rate (Hock 1999). Previous studies have suggested that there is excellent consistency between degree–day models and energy-balance models (WMO 1986; Braithwaite 1995; Hock 1999; Braithwaite and Raper 2002). An extensive discussion of such models can be found in Hock (1999). Such a model has been successfully used in other climate settings (e.g. on Storglacia¨ren glacier (Schneeberger et al. 2001) and on Keqicar Baqi glacier (Zhang et al. 2007). This approach is given by:
ðMF þ aice=snow Ipot ÞTðiÞ : TðiÞ [ 0 MðiÞ ¼ ð2Þ 0 : TðiÞ  0 where i is an index for the elevation band, MF is a melt factor, a is a radiation coefficient which differs for snow and ice surfaces, Ipot is the potential clear-sky direct radiation at the glacier surface, and T is the air temperature of each elevation band. Apart from air temperature, no additional time-dependent meteorological variables are required, and the potential clear-sky direct radiation Ipot is calculated as a function of top-of-atmosphere solar radiation, as assumed atmospheric transmissivity, solar geometry, and topographic characteristics (Garnier and Ohmura 1968):  2 p   dm I ¼S wP0 cosZ cosbcosZ þ sinbsinZ cosðusun  uslope Þ d ð3Þ where S, = 1,360 W m-2, is the solar constant (Peixoto and Oort 1992), (dm/d)2 is the eccentricity correction factor of the Earth’s orbit, w = 0.75 is the mean atmospheric clearsky transmissivity (Hock 1999; Schneeberger et al. 2001; Zhang et al. 2007), P is the atmospheric pressure, P0 is the mean atmospheric pressure at sea level, Z is the zenith

123

64

Environ Geol (2008) 56:59–68

angle, which is approximated as a function of latitude, solar declination, and hour angle (Peixoto and Oot 1992), b is the slope angle, usum is the solar azimuth angle, and uslope is the slope azimuth angle. Potential direct solar radiation is set to zero between sunset and sunrise and for the surface that is shaded by surrounding topography. For the entire Tuotuo River basin, glacier runoff Q on a given day is therefore: n X Q¼ SðiÞ½ð1  f ÞMðiÞ þ Pliq ðiÞ ð4Þ i¼1

where S is the area of an elevation band, Pliq is the liquid precipitation, which is assumed to generate runoff on the glacier surface, and f is the refreezing rate. Refreezing of meltwater must be taken into account in simulating glacier runoff in the Tuotuo River basin where cold-type glaciers are dominant (Huang 1990), because significant amounts of meltwater have been captured as superimposed ice (Fujita et al. 1996). Results from intensive observation of the north slope of the Tanggula Mountains (Ageta and Fujita 1996; Zhang et al. 1997; Fujita et al. 2000; Yao 2002), Fujita et al. (2007) suggested that in the mid to the northern Tibetan Plateau approximately 20% of meltwater is preserved at the snow-ice boundary due to refreezing process. Therefore, herein the refreezing rate f is set to 0.2. Additionally, because of the variation of glacier runoff, primarily depending on changes of glacier area and climatic conditions, the influence of evaporation on the glacier surface on glacier runoff is significantly small (Yang 1991; Ye et al. 1996; Zhang et al. 1997; Yao 2002). Therefore, the impact of evaporation on the glacier surface on glacier runoff is not taken into account.

Verification In addition to the above-mentioned fixed model parameters (Table 3), the melt factor MF and the radiation coefficient asnow/ice need to be determined. Note that there is no monitored glacier in the source region of Yangtze River Table 3 Parameter values of the model for the Tuotuo River basin Parameter

Value

Unit

Temperature lapse rate

-0.50

°C/(100 m)

Precipitation gradient

11.2

%/(100 m)

Threshold temperature

2.0

°C

Refreezing rate

0.2

–

Melt factor

2.1

mm/(d°C)

Radiation coefficient for ice

14.4 9 10-6

m3/(W d°C)

Radiation coefficient for snow

6.1 9 10-6

m3/(W d°C)

123

with the exception of the Dongkemadi River basin located on the north slope of Tanggula Mountains. Zhang et al. (2006d) analyzed the spatial variation of degree–day factors based on glacier melt data and meteorological data in different periods in western China; the results suggested that the regional patterns of degree–day factors are detectable on the glaciers because of the unique climatic environment and heat budget of the Tibetan Plateau and surrounding regions. In the modified degree–day model, the degree–day factor is modified as a function of potential direct solar radiation and the melt factor (Hock 1999). Therefore, MF, aice and asnow can be obtained on the basis of observational results from different periods on the north slope of the Tanggula Mountains (Yao 2002; Yang et al. 2006) and the regional patterns of degree–day factors in the source region of Yangtze River suggested by Zhang et al. (2006d), which are given in Table 3. On the basis of these parameters of the model (Table 3), glacier runoff in the glaciated regions was computed from meltwater and rainwater over the period from 1961 to 2004. Because of the sparsity of measured glacier runoff in the glaciated regions of the Tuotuo River basin, it is difficult to assess the performance of the above-mentioned model using the measured data. Therefore, the total change of ice volume in the Tuotuo River basin for the period 1968–2002 was used to assess the performance of such model. This was estimated by using a modified equation suggested by Liu et al. (2003). The equation is V = 0.04 9 S1.35, where V is the ice volume (km3) and S is the area of the glaciers (km2). This empirical equation is derived from ice-penetrating radar thickness measurements of six valley glaciers, five cirque glaciers, one hanging glacier, one ice cap, and three cirque-hanging glaciers (area 0.46–165 km2) in the Tien Shan and seven glaciers (area 0.1–7 km2) in the Qilian Shan, and from measurements in the Qinghai-Tibetan Plateau (Liu et al. 2003). This equation has been widely applied to estimate glacier volume in the different glaciated regions in western China (Shuangguan et al. 2004; Liu et al. 2004, 2006a, b). On the basis of the glacier area of the Tuotuo River basin in different periods, a decrease in the ice volume of glaciers is estimated, which is approximately 54.6 9 108 m3 water equivalent (assuming an ice density of 900 kg m-3) during the period 1968–2002. In other words, water resources in the Tuotuo River basin increased by approximately 54.6 9 108 m3 as a result of the loss of ice volume during the period studied. In the same period, estimated glacier runoff is approximately 58.2 9 108 m3 in the Tuotuo River basin, which agrees closely with the increase in water resources because of ice mass loss in the river basin for the period 1968–2002 (54.6 9 108 m3 vs. 58.2 9 108 m3), with a relative error of only 6.5%. Note that the loss of ice volume includes glacier melt and evaporation. However,

Environ Geol (2008) 56:59–68

evaporation from the glacier surface cannot be estimated because of the sparsity of meteorological data in the glaciated regions of the Tuotuo River basin. On the basis of observational data obtained in the Dongkemadi River basin located on the north slope of Tanggula Mountains, annual evaporation on the glacier surface is estimated to account for approximately 6% of total river runoff in the river basin (Yao 2002). On the other hand, potential evaporation in the Tibetan Plateau was simulated by using the Penman– Monteith model, which indicated that potential evaporation in the Tuotuo River basin gradually decreases over the period 1971–2000 (Wu et al. 2005). Therefore, the influence of evaporation on the glacier surface is not taken into account in this study. It can be seen that the above-mentioned model performs well with respect to glacier runoff, and its results can be regarded as acceptable for the Tuotuo River basin, where there are no observation data of glacier runoff and no correlative study.

Glacier runoff variation and its possible influence As indicated in Fig. 4, the river runoff in the Tuotuo River basin displayed a marked decreasing trend from the early 1960s to the late 1980s, and this began to become a dramatic increase from the early 1990s. From Fig. 4 it can be seen that there has been a general increase in glacier runoff in the river basin. Since the early 1990s, especially, this trend has become more pronounced. The contribution of glacier runoff to total river runoff in the Tuotuo River basin is approximately 32% for the period from 1968 to 2004 and up to approximately 47.4% in the 1990s. However, recent studies have shown that precipitation in the Tuotuo River basin has experienced a decrease–increase–decrease trend

65

during the 1960s–1990s, which implies that the climate in the river basin is, perhaps, shifting from cold–wet toward warm–dry (Yang et al. 2004; Zhang et al. 2006b; Wang et al. 2007). The minimum of precipitation occurs in the Tuotuo River basin in the 1990s, especially in summer, during which precipitation shows a significant decrease trend (Zhang et al. 2006b). This implies that the increase in the river runoff of the river basin since the early 1990s is very likely to be because of the influence of rapid increase in glacier runoff. With the marked increase in temperature and glacier shrinkage in the Tuotuo River basin since the early 1990s, an increasing amount of additional fresh water is very likely to be released from glacier storage, resulting in a dramatic increase in glacier runoff (Fig. 5). Relative to the period 1961–1990, the discharge anomalies of glacier runoff are almost positive since the early 1990s and display an increasing trend (Fig. 5). In 2002 discharge of glacier runoff reached a maximum during recent decades, and increased by approximately 52% compared with the mean value over the period 1961–1990. These results reveal that river runoff has increased by approximately 9.4% in the entire Tuotuo River basin since the early 1990s compared with the mean value for the period 1961–1990, because of two-thirds of which were derived from the contribution of glacier runoff. This rapid increase in glacier runoff indicates, to a great extent, that the influence of glacier runoff on the river runoff has become much greater than ever before, especially since the early 1990s when precipitation has displayed a decreasing trend in the Tuotuo River basin.

Discussion and conclusion Although glaciers show a rapid retreat in the Tuotuo River basin since the early 1990s, on the whole, glacier changes

Fig. 4 Annual discharge of river runoff and glacier runoff in the Tuotuo River basin during recent decades. Dashed lines are the fiveyear smoothing average and the dotted curves are their second-order polynomial fit curves

Fig. 5 Glacier runoff anomaly since the early 1990s relative to the period 1961–1990. The solid line is the linear trend

123

66 Table 4 Comparison of glacier changes in Tibetan Plateau, western China

Environ Geol (2008) 56:59–68

Region

Time-span

Area change (%)

Data source

A0 nyeˆmaqeˆn Mountain

1966–2000

-17.0

Liu et al. 2002

Xinqingfeng ice cap

1973–2000

-1.6

Liu et al. 2004

Karakoram

1969–1999

-4.1

Shangguan et al. 2006

Tuotuo River basin

1968/1971–2001/2002

-3.2

This study

Nyainqen Tanglha

1970–2000

-5.7

Shangguan et al. 2006

Pengqu Basin

1979–2000/2001

-9.0

Jin et al. 2005

Naimona’nyi

1976–2003

-8.8

Ye et al. 2006b

during recent decades are relatively small compared with glacier changes in other regions of the Tibetan Plateau (Table 4). As indicated in Table 4, glacier changes in the Tuotuo River basin are the smallest with the exception of the Xinqingfeng ice cap in the Tibetan plateau. Because glaciers in the Tuotuo River basin are all the cold-type or polar-type glaciers, it is possible that their slower dynamic response to climate change can explain why they have exhibited small changes during recent decades. Therefore, the surface area of glaciers is supposed to be constant throughout a given simulation period of glacier runoff. Previous studies have shown that the glacier runoff response to climate warming is immediate (Chen and Ohmura 1990; Kuhn and Batlogg 1998; Braun et al. 2000). This has recently been tested by the rapid changes in ice discharge from Greenland outlet glaciers (Howat et al. 2007). In the period 2001–2050, the trend in air temperature is likely to increase more in the upper reaches of the Yangtze River than in the middle and down reaches, on the basis of the outputs of the ECHAM5 model (the fifthgeneration atmospheric general circulation model) developed at the Max-Planck-Institute for Meteorology (MPIM) (Zeng et al. 2007). Similarly, Liu et al. (2007) find that air temperature will probably increase in the source region of Yangtze River in the A2 and B1 emission scenarios over the period 2001–2050 based on the outputs of the ECHAM5 model. This shows that there is likely to be increase in temperature in the Tuotuo River basin in the coming decades, which will probably accelerate current glacier retreat. With the continuous retreat of glaciers in the Tuotuo River basin, glacier volume is likely to decrease because of long-term mass loss, which in turn is very likely to lead to reduced water yield of glaciers in the river basin. When glaciers have disappeared in the Tuotuo River basin, glacier runoff is likely to greatly reduce, and then significantly affect the ecological environment and water resources in the river basin. Over the period 1968/1971–2001/2002, most of glaciers in the Tuotuo River basin have been retreating, with a smaller portion advancing. The area of glacier shrinkage in the river basin during recent decades accounts for

123

approximately 3.2% of the total area in the late 1960s. To assess the possible influence of glacier runoff, resulting from the ice mass loss, on river runoff, a modified degree– day model including potential clear-sky direct solar radiation has been applied to the Tuotuo River basin in the source region of Yangtze River, western China. This is the first use of the model in the center of the Tibetan Plateau. The model includes a distinct spatial element by including the potential clear-sky direct solar radiation, and thus the effects of topography on glacier melt are accounted for in the model. In comparison of estimated glacier runoff with the increase in water resources resulting from the decrease in ice volume in the same period the model performs well and its results are acceptable. This shows the model can be also applied to the cold-type glacier in the center of Tibetan Plateau where very few observation data and related studies exist. The results from the model indicate that glacier runoff displays an increase trend caused by icemass loss for the period 1961–2004, and its discharge accounts for 32% of the total discharge of the river runoff in the entire Tuotuo River basin. Since the early 1990s river runoff in the entire basin has increased by approximately 9.4% compared with the mean value for the period 1961–1990, two-third of which is derived from glacier runoff as a result of glacier shrinkage. It can be seen that the rapid increase in glacier runoff plays an important role in the development of the ecological environment and water resources in the Tuotuo River basin. However, because there has been no long-term monitoring of any glacier in the Tuotuo River basin, there are uncertainties in the interpolated meteorological data for different elevation bands of the glaciated regions using the constant lapse rates, especially in the spatial distribution of precipitation. Consequently, this model needs further refinement and development in future work; meanwhile, a more comprehensive glacier-monitoring project is needed in the source region of Yangtze River, western China. Acknowledgments We thank the anonymous reviewers for helpful comments and suggestions, which considerably improved the final manuscript. We also thank the National Climate Center, China Meteorological Administration, for meteorological data from stations

Environ Geol (2008) 56:59–68 in the Tuotuo River basin. This research was supported by the National Natural Science Foundation of China (Grant No. 40701032), the Key Research Project of the Knowledge Innovation Project of Chinese Academy Sciences (CAS) (Grant No. Kzcx2-yw-301), the National Basic Work Program of Chinese MST (Grant No. 2006FY110200) and the National Natural Science Foundation of China (Grant No. 40571034 and No. 40371026).

References Ageta Y, Fujita K (1996) Characteristics of mass balance of summeraccumulation type glaciers in the Himalayas and Tibetan Plateau. Zeitschrift fu¨r Gletscherkunde und Glazialgeologie 32:61–65 Braithwaite RJ (1995) Positive degree–day factor for ablation on the Greenland ice sheet studied by energy-balance modeling. J Glaciol 41(137):153–160 Braithwaite RJ, Raper SCB (2002) Glaciers and their contribution to sea level change. Phys Chem Earth 27:1445–1454 Braun LN, Weber M, Schulz M (2000) Consequences of climate change for runoff from Alpine regions. Ann Glaciol 31:19–25 Chen J, Ohmura A (1990) On the influence of Alpine glaciers on runoff. In: Lang H, Musy A (eds) Hydrology of mountainous regions I. Proceedings of two Lausanne Symposia. IAHS Publ 193, pp 117–126 Ding Y, Li Z, Liu S, Yu X (1992) Glacioclimatological features in the Tanggula Mountains, China. Ann Glaciol 16:1–6 Dwyer JL (1995) Mapping tidewater glacier dynamics in East Greenland using Landsat data. J Glaciol 41(139):584–595 Fujita K, Ageta Y (2000) Effect of summer accumulation on glacier mass balance on the Tibetan Plateau revealed by mass-balance model. J Glaciol 46:244–252 Fujita K, Seko K, Ageta Y, Pu J, Yao T (1996) Superimposed ice in glacier mass balance on the Tibetan Plateau. J Glaciol 42:454– 460 Fujita K, Ageta Y, Pu J, Yao T (2000) Mass balance of Xiao Dongkemadi Glacier on the central Tibetan Plateau from 1989 to 1995. Ann Glaciol 31:159–163 Fujita K, Ohta T, Ageta Y (2007) Characteristics and climatic sensitivities of runoff from a cold-type glacier on the Tibetan Plateau. Hydrol Proc 21:2882–2891 Garnier B, Ohmura A (1968) A method of calculating the direct shortwave radiation income on slopes. J Appl Meteorol 7:796– 800 Hock R (1999) A distributed temperature-index ice and snowmelt model including potential direct solar radiation. J Glaciol 45(149):101–111 Howat IM, Joughin I, Scambos TA (2007) Rapid changes in ice discharge from Greenland outlet glaciers. Science 315:1559– 1561 Huang M (1990) On the temperature distribution of glaciers in China. J Glaciol 36:210–216 Jansson P, Hock R, Schneider T (2003) The concept of glacier storage––a review. J Hydrol 282:115–29 Jin R, Li X, Chen T, Wu L, Mool P (2005) Glacier area changes in the Pumqu River basin, Tibetan Plateau, between the 1970s and 2001. J Glaciol 51:607–610 Kang S, Zhang Y, Qin D, Ren J, Zhang Q, Bjorn G, Paul AM (2007) Recent temperature increase recorded in an ice core in the source region of Yangtze River. Chin Sci Bull 52(6):825–831 Kuhn M, Batlogg N (1998) Glacier runoff in Alpine headwaters in a changing climate. In: Kovar KU, Tappeiner N, Peters E (eds) Hydrology, water resources and ecology in headwaters. IAHS Publ 248, pp 78–88

67 Lemke P, Ren J, Alley R B, Allison I, Carrasco J, Flato G, Fujii Y, Kaser G., Mote P, Thomas RH, Zhang T (2007) Observations: changes in snow, ice and frozen ground. In: Solomon S, Qin D, Manning M, Chen Z, Marquis M, Averyt KB, Tignor M, Miller HL (eds) Climate change 2007––The physical science basis. Contribution of working Group I to the fourth assessment report of the international panel on climate change. Cambridge University Press, Cambridge, pp 356–360 Li Z, Sun W, Zeng Q (1998) Measurements of glacier variation in the Tibetan Plateau using Landsat data. Remote Sens Environ 63:258–264 Li X, Cheng G, Lu L (2003) Comparison study of spatial interpolation methods of air temperature over Qinghai-Xizang plateau (in Chinese). Plateau Meteorology 22(6):565–573 Liu S, Lu A, Ding Y, Yao T, Ding L, Li G, Hook RL (2002) Glacier fluctuations and the inferred climate changes in the A0 nyeˆmaqeˆn Mountain in the source area of the Yellow River (in Chinese). J Glaciol Geocryol 24:701–707 Liu S, Sun W, Shen Y, Li G (2003) Glacier changes since the Little Ice Age Maximum in the western Qilian Mountains, northwest China. J Glaciol 49(164):117–124 Liu S, Shangguan D, Ding Y, Zhang Y, Wang J, Han H, Xie C, Ding L, Li G (2004) Variation of glaciers studied on the basis of RS and GIS––A reassessment of the changes of the Xinqingfeng and Malan Ice Caps in the Northern Tibetan Plateau (in Chinese). J Glaciol Geocryol 26(3):244–252 Liu S, Ding Y, Shangguan D, Zhang Y, Li J, Han H, Wang J, Xie C (2006a) Glacier retreat as a result of climate change due to warming and increased precipitation in the Tarim River Basin, Northwest China. Ann Glaciol 43:91–96 Liu S, Shangguan D, Ding Y, Han H, Xie C, Zhang Y, Li J, Wang J, Li G (2006b) Glacier changes during the past century in the Gangrigabu mountains, southeast Qinghai–Xizang (Tibetan) Plateau, China. Ann Glaciol 43:187–193 Liu S, Zhang Y, Zhang Y, Ding Y (2007) Modeling glacier runoff and its trend in the source region of Yangtze River, China. Sci China Ser D Earth Sci (in press) Lu A, Yao T, Liu S, Ding L, Li G (2002) Glacier change in the Geladandong area of the Tibetan Plateau monitored by remote sensing (in Chinese). J Glaciol Geocryol 24(5):559–562 Meehl GA, Stocker TF, Collins WD, Friedlingstein P, Gaye AT, Gregory JM, Kitoh A, Knutti R, Murphy JM, Noda A, Raper SCB, Watterson IG, Weaver AJ, Zhao Z-C (2007) Global climate projections. In: Solomon S, Qin D, Manning M, Chen Z, Marquis M, Averyt KB, Tignor M, Miller HL (eds) Climate change 2007– The physical science basis. Contribution of working Group I to the fourth assessment report of the international panel on climate change. Cambridge University Press, Cambridge, pp 814–816 Paul F (2000) Evaluation of different methods for glacier mapping using Landsat TM. In: Proceedings of 20th EARSeL symposium––land ice and snow. Dresden, European Association of Remote-Sensing Laboratories, pp 239–245 Paul F (2002) Changes in glacier area in Tyrol, Austria, between 1969 and 1992 derived from Landsat TM and Austrian glacier inventory data. Int J Remote Sens 23(4):787–799 Paul F, Ka¨a¨b A, Maisch M, Kellenberger T, Haeberli W (2002) The new remote-sensing-derived Swiss glacier inventory. I. Methods. Ann Glaciol 34:355–361 Paul F, Huggel C, Ka¨a¨b A (2004) Combining satellite multispectral image data and a digital elevation model for mapping debriscovered glaciers. Remote Sens Environ 89:510–518 Peixoto JP, Oort AH (1992) Physics of climate. American Institute of Physics, New York, pp 91–130 Rott H (1994) Thematic studies in alpine areas by means of polarimetric SAR and optical imagery. Adv Space Res 14(3):217–226

123

68 Schneeberger C, Albrecht O, Blatter H (2001) Modelling the response of glaciers to a doubling in atmospheric CO2: a case study of Storglaciaren, northern Sweden. Clim Dyn 17:825–834 Shangguan D, Liu S, Ding Y, Ding L, Li G (2004) Glacier changes at the head of Yurungkax River in the west Kunlun Mountains in the past 32 years (in Chinese). Acta Geogr Sin 59(6):855– 862 Shangguan D, Liu S, Ding Y, Ding L, Xiong L, Cai D, Li G, Lu A, Zhang S, Zhang Y (2006) Monitoring the glacier changes in the Muztag Ata and Konggur Mountains, east Pamirs, based on Chinese Glacier Inventory and recent satellite imagery. Ann Glaciol 43:79–85 Shi Y, Liu C, Wang Z, Liu S, Ye B (2005) A concise China glacier inventory (in Chinese). Shanghai Science Popularization, Shanghai, pp 111–127 Trenberth KE, Jones PD, Ambenje P, Bojariu R, Easterling D, Klein Tank A, Parker D, Rahimzadeh F, Renwick JA, Rusticucci M, Soden B, Zhai P (2007) Observations: surface and atmospheric climate change. In: Solomon S, Qin D, Manning M, Chen Z, Marquis M, Averyt KB, Tignor M, Miller HL (eds) Climate change 2007––The physical science basis. Contribution of working group I to the fourth assessment report of the international panel on climate change. Cambridge University Press, Cambridge, pp 237–239 Wang G, Li Y, Wang Y, Shen Y (2007) Impacts of Alpine ecosystem and climate changes on surface runoff in the headwaters of the Yangtze River (in Chinese). J Glaciol Geocryol 29(2):159–168 WMO (1986) Intercomparison of models for snowmelt runoff. Operational Hydrology Report 23(WMO No.646) Wu L, Li X (2004) China glacier information system (in Chinese). China Ocean Press, Beijing, pp 23–78 Wu S, Yin Y, Zheng D, Yang Q (2005) Climate changes in the Tibetan Plateau during the last three decades (in Chinese). Acta Geogr Sin 60(1):3–11 Xie C, Ding Y, Liu S, Wang G (2003) Comparison analysis of runoff change in the source regions of the Yangtze and Yellow Rivers (in Chinese). J Glaciol Geocryol 25(4):414–422 Yang J, Ding Y, Shen Y, Liu S, Chen R (2004) Climatic features of eco-environment change in the source regions of the Yangtze and Yellow Rivers in recent 40 years (in Chinese). J Glaciol Geocryol 26(1):7–16 Yang J, Ding Y, Chen R, Liu J (2006) Synthetical study of EcoEnvironmental changes in the source regions of the Changjiang and Huanghe Rivers (in Chinese). Meteorological Press, Beijing, pp 102–115

123

Environ Geol (2008) 56:59–68 Yang Z (1991) Glacier water resources in China (in Chinese). Gansu Science Technology Publishing House, Lanzhou, pp 115–153 Yao T (2002) Trend features of cryophere in the centre of Tibetan Plateau (in Chinese). Geological Publishing House, Beijing, pp 169–206 Yao T, Liu S, Pu J, Shen Y, Lu A (2004) The recent retreat of glacier in high Asia and its influence on the water resources of Northwest in China. Sci China Ser D-Earth Sci 34(6):535–543 Ye B, Chen K, Shi Y (1996) Responses of glacier and glacial runoff to climatic change—A model in simulating the Glacier No. 1 in headwaters of the Urumqi River (in Chinese). Scientia Geographica Sinica 17(1):32–40 Ye B, Yang D, Ding Y, Han T, Toshio K (2004) A bias-corrected precipitation climatology for China. J Hydrometeorol 5:1147– 1160 Ye Q, Kang S, Chen F, Wang J (2006a) Monitoring glacier variations on Geladandong mountain, central Tibetan Plateau, from 1969 to 2002 using remote-sensing and GIS technologies. J Glaciol 52(179):537–545 Ye Q, Yao T, Kang S, Chen F, Wang J (2006b) Glacier variations in the Naimona’nyi region, western Himalaya, in the last three decades. Ann Glaciol 43:385–389 Zeng X, Su B, Jiang T, Chen Z (2007) Projection of future climate change in the Yangtze River basin for 2001–2050 (in Chinese). Advances in Clim Chang Res 3(5):293–298 Zhang Y, Yao T, Pu J, Xiao C, Kang S, Hou S, Ohta T, Yabuki H (1997) The features of hydrological processes in the Dongkemadi River basin, Tanggula Pass, Tibetan Plateau(in Chinese). J Glaciol Geocryol 19(3):214–222 Zhang Q, Kang S, Yan Y (2006a) Characteristics of spatial and temporal variations of monthly mean surface air temperature over Qinghai-Tibet Plateau. Chin Geogr Sci 16(4):351–358 Zhang G, Shi X, Li D, Wang Q, Dai S (2006b) Climate change in Tuotuohe area at the headwaters of Yangtze River (in Chinese). J Glaciol Geocryol 28(5):678–685 Zhang Y, Liu S, Ding Y, Li J, Shangguan D (2006c) Preliminary study of mass balance on the Keqicar Baxi glacier on the south slopes of Tianshan Mountains (in Chinese). J Glaciol Geocryol 28(4):477–484 Zhang Y, Liu S, Ding Y (2006d) Observed degree–day factors and their spatial variation on glaciers in western China. Ann Glaciol 43:301–306 Zhang Y, Liu S, Ding Y (2007) Glacier meltwater and runoff modelling, Keqicar Baqi Glacier, southwestern Tien Shan, China. J Glaciol 180(53):91–98