SCIENCE CHINA Earth Sciences • RESEARCH PAPER •
June 2010 Vol.53 No.6: 880–891 doi: 10.1007/s11430-010-0073-4
Glacier runoff variation and its influence on river runoff during 1961–2006 in the Tarim River Basin, China GAO Xin1,2*, YE BaiSheng1,2, ZHANG ShiQiang2, QIAO ChengJun1,2 & ZHANG XiaoWen3 1
2
State Key Laboratory of Cryospheric Sciences CAREERI, Chinese Academy of Sciences, Lanzhou 730000, China; Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000, China; 3 The Resource Environment and Urban and Rural Planning Department, Lanzhou Commercial College, Lanzhou 730020, China Received September 15, 2009; accepted March 8, 2010; published online May 12, 2010
Using monthly precipitation and temperature data from national meteorological stations, 90 m resolution DEM and a digital vector map of modern glaciers from the Chinese Glacier Inventory, the glacier mass balance and glacier runoff in the Tarim River Basin (TRB), China, were estimated based on a monthly degree-day model for 1961–2006. The results suggest that the modified monthly degree-day model can simulate the long-term changes in glacier mass balance and glacier runoff, which have been confirmed by short-term observation data and other results in literatures. The characteristics and trends of mass balance and glacier runoff variation were analyzed. It was found that the mean annual glacier mass balance during 1961–2006 was −139.2 mm per year and the cumulative mass balance over the 46 year period was −6.4 m in the TRB. The glacier mass balance displayed a clear decreasing trend over the entire TRB during 1961–2006. The average annual glacier runoff in the TRB was 144.16×108 m3 for 1961–2006. The results also show that glacier runoff has increased in the last 46 years, especially since the 1990s with 85.7% of the increased river flow being derived from the increased glacier runoff caused by loss of ice mass. Over the entire TRB, glacier runoff accounts for 41.5% of the total river flow during 1961–2006. The impact of glacier runoff on river flow has increased in the TRB as a result of glacier shrinkage. glacier mass balance, degree-day model, glacier runoff, Tarim River Basin Citation:
Gao X, Ye B S, Zhang S Q, et al. Glacier runoff variation and its influence on river runoff during 1961–2006 in the Tarim River Basin, China. Sci China Earth Sci, 2010, 53: 880–891, doi: 10.1007/s11430-010-0073-4
Large and widely distributed glaciers are an important component of surface water resources and glacier runoff provides precious freshwater for arid and semi-arid regions in western China [1]. Glacier runoff significantly affects catchment hydrology by temporarily storing and releasing water on various time scales. The glacier mass balance reflects the response of glacier movement to climate change and controls stream flow changes and glacier variations [2–4]. Thus, measurement of glacier mass balance and the
*Corresponding author (email:
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© Science China Press and Springer-Verlag Berlin Heidelberg 2010
assessment of glacier runoff are becoming key scientific issues. Since the beginning of the 20th century, mountain glaciers have generally experienced worldwide retreat and thinning in response to a 0.74°C increase in global mean surface temperature [5, 6]. Climate warming has been the main cause for the retreat of glaciers in recent decades. In 1986/1987, a climatic shift to a warm-wet pattern occurred, causing reductions in glacier area and volume which had a considerable impact on the variability of runoff [7]. Little is known about how glacier runoff has changed in the past few decades and the consequent impact on water resources and the ecological environment. earth.scichina.com
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GAO Xin, et al.
Sci China Earth Sci
Located in an arid area in northwestern China, the Tarim River is the largest inland river in China. The runoff derived from snow and ice plays a crucial role in regional water resources in the Tarim River Basin (TRB). Glacier runoff accounts for approximately 38.5% of the total river flow in the TRB [8]. Because of the limited number of studied glaciers in the TRB, it is difficult to obtain the long-term glacier mass balance and glacier runoff for the whole basin. Using methods of statistical mechanics and the maximum entropy principle, one can describe the distributions of precipitation, mean depth and coefficient of runoff in a watershed with a negative exponential function [9]. Using this method, Shen et al. [10] calculated the glacier mass balance during 1957–2000 for Tailan River Basin. Another method for calculating the glacier mass balance uses remote sensing data to analyze glacier changes, and then calculate variations in the ice volume and estimate its contribution to the river runoff [11]. However, these methods could not analyze the connections between glacier, climate and runoff for the entire TRB. The objective of this study is to use a modified monthly degree-day model [12, 13] to simulate the glacier mass balance and glacier runoff. We also analyzed the characteristics of glacier runoff variation and its possible effects on water resources in the TRB for the period 1961–2006.
1
Study area
Located in an arid area in northwestern China, the TRB is the largest inland river in China, with a total area of about 1.02×106 km2. The TRB is composed of 114 rivers in nine river systems surrounding the TRB. With the intensive disturbance of human activities, especially the exploitation of
Figure 1
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water resources, great changes have occurred in recent decades. The river systems have been disturbed to such a degree that only three river systems (the Aksu, Hotan and Yarkant rivers) still retain their natural hydraulic relationship with the mainstream [14] (Figure 1). Among the three main headstreams, the proportions of water recharge from the Aksu, Hotan and Yarkant rivers account for 73.2%, 23.2% and 3.6%, respectively [15]. The Kaidu River sometimes transports water to the irrigation area in the lower reaches of the Tarim River from Bosten Lake [14]. The mainstream of the Tarim River is 1321 km. The main water sources for the Tarim River originate from the Tianshan, Kunlun and Karakorum mountains (Figure 1). The TRB has an extreme drought desert climate with an average annual temperature of 10.6–11.5°C, precipitation of 17.4–42.0 mm and evaporation of 1125–1600 mm [14]. The Chinese Glacier Inventory (CGI) shows that there are 11665 glaciers in the TRB with a total area of 19877.7 km2 and a total volume of 2313.29 km3, accounting for 25.2%, 33.5% and 41.3% of the total number, area and volume, respectively, of all glaciers in China [16]. The glaciers are located mainly in the Yarkant, Hotan, Aksu, Keliya and Kaxgar river watersheds, and glacier runoff in the Tarim River originates principally from these rivers.
2 2.1
Data and methods Data collection
Our study is based on various datasets including monthly temperature and precipitation data for 1961–2006 from national meteorological stations, annual discharge of mountain river runoff from hydrological stations in the TRB (Figure 1), the sub-basin boundaries of the TRB, a digital elevation
Sketch map of the river system, hydrological stations, meteorological stations and glacier distribution in the TRB.
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Sci China Earth Sci
model (DEM) with 90 m resolution derived from 1:250000 topographic maps, and the glacier area data in the TRB taken directly from the CGI, which was mainly derived from topographical maps (1:100000) based on aerial photos acquired during 1962–1977. 2.2
Methods
Glacier mass balance and glacier runoff simulations are carried out in monthly time steps using a modified degree-day model. The model was modified to monthly time steps (Figure 2) on the principals of the original degree-day model. The degree-day model is based on an assumed relationship between ablation and air temperature usually expressed in the form of positive temperature sums, which is given by refs. [17, 18] A=DDF·PDD,
(1)
where DDF is the degree-day factors which are different for snow and ice surfaces (mm d−1 °C −1), A is the depth of
Figure 2
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meltwater (mm), and PDD is the monthly positive accumulated air temperature, which is given by [19] PDD =
n
Ht ⋅ Tt , ∑ i =1
(2)
where Tt is the monthly mean air temperature, and Ht is a logical variable, which can be defined such that Ht=1 for Tt≥0°C and Ht=0 for Tt
