Science of the Total Environment 527–528 (2015) 26–37

Contents lists available at ScienceDirect

Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv

Stable isotopes reveal sources of precipitation in the Qinghai Lake Basin of the northeastern Tibetan Plateau Bu-Li Cui a,c,⁎, Xiao-Yan Li b,c a b c

State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061, China State Key Laboratory of Earth Surface Processes and Resource Ecology, Beijing Normal University, Beijing 100875, China College of Resources Science and Technology, Beijing Normal University, Beijing 100875, China

H I G H L I G H T S • Stable isotopes reveal sources of precipitation in the Qinghai Lake Basin. • Southwest Asian Monsoon could not reach the northeastern Tibetan Plateau. • Vapor contribution from lake evaporation to precipitation cannot be ignored.

a r t i c l e

i n f o

Article history: Received 21 July 2014 Received in revised form 26 February 2015 Available online xxxx Editor: D. Barcelo Keywords: Stable isotope Deuterium excess Precipitation Moisture cycling The Qinghai Lake Basin

a b s t r a c t The use of isotopic tracers is an effective approach for characterizing the moisture sources of precipitation in cold and arid regions, especially in the Tibetan Plateau (TP), an area of sparse human habitation with few weather and hydrological stations. This study investigated stable isotope characteristics of precipitation in the Qinghai Lake Basin, analyzed moisture sources using data sets from NCEP–NCAR, and calculated vapor contributions from lake evaporation to the precipitation in the basin using a two-component mixing model. Results showed that the Local Meteoric Water Line (LMWL) was defined as δ2H = 7.86 δ18O + 15.01, with a slope of less than 8, indicating that some non-equilibrium evaporation processes occurred when the drops fell below the cloud base. Temperature effects controlled δ18O and δ2H in precipitation in the basin, with high values in summer season and low values in winter season. Moisture in the basin was derived predominantly from the Southeast Asian Monsoon (SEAM) from June to August and the Westerly Circulation (WC) from September through May. Meanwhile, the transition in atmospheric circulation took place in June and September. The SEAM strengthened gradually, while the WC weakened gradually in June, and inversely in September. However, the Southwest Asian Monsoon (SWAM) did not reach the Qinghai Lake Basin due to the barrier posed by Tanggula Mountain. High d-excess (N10‰) and significant altitude and lake effects of δ18O in precipitation suggested that the vapor evaporated from Qinghai Lake, strongly influenced annual precipitation, and affected the regional water cycle in the basin distinctly. The monthly contribution of lake evaporation to basin precipitation ranged from 3.03% to 37.93%, with an annual contribution of 23.42% or 90.54 mm, the majority of which occurred in the summer season. The findings demonstrate that the contribution of evaporation from lakes to atmospheric vapor is fundamental to water cycling on the TP. © 2015 Elsevier B.V. All rights reserved.

1. Introduction Precipitation is an important component of total water resources, making it vital for irrigation, industrial and domestic uses in inland regions. Terrestrial moisture produced by evaporation has been recognized as an important component of the local precipitation (Savenije, 1995; Trenberth, 1999; Trenberth et al., 2003; Bisselink and Dolman, ⁎ Corresponding author at: Institute of Earth Environment, Chinese Academy of Sciences, No. 97 Yanxiang Street, Xi'an, Shanxi, 710061, China. E-mail address: [email protected] (B.-L. Cui).

http://dx.doi.org/10.1016/j.scitotenv.2015.04.105 0048-9697/© 2015 Elsevier B.V. All rights reserved.

2009; Seneviratne et al., 2010), especially in the vicinity of large lake systems, where water evaporates from the surface and exerts a direct influence on the climate of surrounding areas (Scott & Huff, 1996, Schaetzl, 2002, Henne et al., 2007). Using an isotopic technique, Gat and Matsui (1991) calculated that evaporation from the surface of fresh water bodies provided approximately 20–40% of local atmospheric vapor in the Amazon basin. Similarly, Gat et al. (1994) estimated the contribution of evaporation from North America's Great Lakes to the continental atmosphere of the entire region to be ~ 5–16% in the summer season, and Yamanaka and Shimizu (2007) calculated the contribution of various vapor sources and lake evaporation to the local

B.-L. Cui, X.-Y. Li / Science of the Total Environment 527–528 (2015) 26–37

27

Fig. 1. Location of the Qinghai Lake Basin and sites for sampling precipitation and lake water.

decline of 4.75 cm over the 53-year period (Li et al., 2012). These hydrological processes have contributed to a series of environmental problems in the basin, such as desertification, erosion, loss of grazing grassland, and deterioration of water quality and quantity (Qin and Huang, 1998; Hao, 2008). However, the lake level rose from 3192.87 m in 2004 to 3194.08 m in 2012, with an average annual increase of 15.1 cm over the 8 years (Jin et al., 2013). The variation of lake level chiefly depended upon climate change and runoff, especially precipitation (Li et al., 2007; Zhang et al., 2011; Jin et al., 2013). Owing to the closed basin of the lake, precipitation is the sole source of water input into the basin, meaning that precipitation directly sustains the lake level and the security of water resources in the Qinghai Lake Basin. Therefore, studies of the sources of precipitation and their spatial and temporal characteristics are crucial to understanding and managing the ecology of the Qinghai Lake Basin. Such research is the prerequisite for assessing the process of water cycling and identifying the reasons for lake level changes, and it will contribute to planning strategies and 0

δ2H/‰

atmosphere of the Kasumigaura lake region in the Eastern Japan. Such studies have also been carried out in regions around the Mediterranean, Caspian, and Aral Seas (Gat and Carmi, 1970; Aizen et al., 1996; Kattan, 1997; Kreutz et al., 2003; Machavaram and Krishnamurthy, 1995). That body of research demonstrates that the contribution of evaporation from lakes to local atmospheric vapor plays an integral role in large lake systems, and that isotopic tracers are an effective approach for investigating complex hydrological processes including estimating the contribution of evaporation from water surfaces to local precipitation. The Tibetan Plateau (TP) is a cold-arid region with more than 1500 lakes that cover a total lake area of 44,993.3 km2 (Xu et al., 2011; Song et al., 2014a). Strong heat during the spring and summer influences the formation of the Indian monsoon and the global atmospheric cycle (Luo and Yanai, 1984; Yanai et al., 1992; Wang et al., 2008), Thus, the contribution of the evaporation from lakes to total atmospheric vapor cannot be ignored in any study of water cycling on the TP. However, due to its large area, complex geological and geomorphic conditions, and paucity of weather and hydrological stations, traditional hydrological methods cannot provide accurate measures of the spatial and temporal characteristics and sources of precipitation on the TP (Liu et al., 2008; Kong and Pang, 2011; Xu et al., 2011). Due to those limitations, quantitative studies on the contribution of terrestrial moisture to total atmospheric moisture on the TP are lacking. The largest lake in China, Qinghai Lake, lies in the cold and semiarid region of the northeastern Tibetan Plateau (Fig. 1). It has an area of 4400 km2 and receives drainage from a catchment area of 29,661 km2. Qinghai Lake is a national nature reserve and an important water body that influences the ecological integrity of the entire region (Tang et al., 1992). In recent decades, 50% of the rivers flowing into the lake have dried up due to climate change and human activity (LZBCAS, 1994; Li et al., 2007), and the elevation of lake level has declined from 3196.55 m in 1959 to 3194.08 m in 2012, with an average annual

LMWL: δ2 H = 7.86 δ18 O + 15.01 R2 = 0.987

-50

-100 Vapor

Liquid

-150 GMWL: δ2 H = 8 δ18 O + 10 -200 -30

-25

-20

-15 δ18O/‰

-10

-5

0

Fig. 2. The relationship between δ2H and δ18O of precipitation in the Qinghai Lake Basin. LMWL, Local Meteoric Water Line; GMWL, Global Meteoric Water Line.

B.-L. Cui, X.-Y. Li / Science of the Total Environment 527–528 (2015) 26–37

5

-10

-5

-15

-15

-20

-25

0

-35 -45

-200

4

5

6 7 Month

8

-15

-120

-30 3

-5

-80

-25 2

5

-40

-160

1

15

9 10 11 12

-25

Temperature/ oC

15 δ2 H/‰

0 -5

Temperature/ oC

δ18 O/‰

28

-35 -45 1

2

3

4

5

6 7 8 Month

9 10 11 12

δ18O of precipitation

δ2H of precipitation

T emprature of T ianjun

T emperature of Gangcha

Fig. 3. Content of δ18O and δ2H in precipitation and temperature of the Qinghai Lake Basin.

40

d-excess/‰

d-excess

average d-excess

30

20 10

0 1

2

3

4

5

6 7 Month

8

9

10

11

12

Fig. 4. Values of d-excess in precipitation of the Qinghai Lake Basin.

recommendations for the rational use of water resources in the basin (Adams et al., 2001; Edmunds et al., 2006; Chang and Wang, 2010). More importantly, the basin lies in a critical transitional zone (Fig. 1) where the Southeast Asian Monsoon (SEAM), the Westerly Circulation (WC) and the Qinghai–Tibet Plateau Monsoon meet (LZBCAS, 1994), making the sources of moisture and the distribution of precipitation highly complex and peculiar (Wang et al., 2004, 2006; Xu et al., 2007; Henderson et al., 2010). The longest and highest-resolution drill core from Qinghai Lake uniquely recorded the variability of the Westerlies

and the Asian summer monsoon since 32 ka, reflecting the interplay between the two systems (An et al., 2012). The contributions of different moisture sources to precipitation in the basin remain unclear thoughin particular, the cycling of moisture from lake evaporation to local precipitation has never been studied in the basin. Therefore, the objectives of this study were to use the 2H and 18O of precipitation as tracers to: (1) investigate the spatial and temporal characteristics of precipitation in the Qinghai Lake Basin; (2) reveal the sources of moisture that contribute to precipitation in the basin;

Table 1 Altitude effect and lake effect of δ18O in precipitation of the Qinghai Lake Basin. Effect type

Time period

Equations

n

R2

R

P

Altitude effect

Annual January February March April May June July August September October November December Annual April May June July August September October

δ18O = −0.002 Alt − 1.03 δ18O = −0.0066 Alt + 4.53 δ18O = −0.00001 − 20.21 δ18O = −0.014 Alt + 34.36 δ18O = −0.005 Alt + 2.90 δ18O = −0.003 Alt + 0.61 δ18O = −0.0018 Alt − 1.73 δ18O = −0.001 Alt − 1.99 δ18O = 0.0018 Alt − 13.66 δ18O = −0.0056 Alt + 6.76 δ18O = −0.0051 Alt + 6.99 δ18O = −0.0009 Alt − 9.87 δ18O = −0.0069 Alt + 7.11 δ18O = −0.0116 Dis − 7.65 δ18O = −0.0221 Dis − 12.63 δ18O = −0.0132 Dis − 8.53 δ18O = −0.0144 Dis − 6.65 δ18O = −0.0058 Dis − 4.97 δ18O = 0.0054 Dis − 7.77 δ18O = −0.0216 Dis − 10.85 δ18O = −0.0445 Dis − 6.73

14 10 10 9 10 14 14 14 13 12 8 8 2 14 10 14 14 14 13 12 8

0.430 0.470 0.000 0.479 0.175 0.484 0.098 0.027 0.130 0.419 0.154 0.008 – 0.510 0.181 0.428 0.277 0.040 0.051 0.246 0.530

−0.656 −0.685 −0.008 −0.692 −0.418 −0.696 −0.314 −0.163 0.361 −0.647 −0.392 −0.088 – −0.714 −0.425 −0.654 −0.526 −0.200 0.225 −0.496 −0.728

P b 0.01 P b 0.02 – P b 0.02 – P b 0.01 – – – P b 0.02 – – – P b 0.01 – P b 0.01 P b 0.05 – – – P b 0.02

Lake effect

B.-L. Cui, X.-Y. Li / Science of the Total Environment 527–528 (2015) 26–37

and (3) analyze the contribution of vapor from lake evaporation to the total basin precipitation. The results will provide valuable insight about the hydrological processes of precipitation in cold and arid alpine environments, and will thus be able to inform water resource management in the Qinghai Lake Basin and the northeastern Tibetan Plateau. 2. Methods 2.1. Background of the Tibetan lakes and Qinghai Lake The Tibetan Plateau (TP) is located in central Asia (25°59′N-40°29′N, 73°27′E-104°30′E). It is also known as the earth's “third pole”, with an average elevation exceeding 4000 m, and as the Asian Water Tower (Yanai et al., 1992). There are more than 1500 lakes on the TP (Song

29

et al., 2014a). Three hundred and twelve lakes cover surface areas larger than 10 km2, 104 lakes cover surface areas larger than 100 km2, and three lakes cover surface areas larger than 1000 km2. The combined lake area of the TP accounts for about 49% of China's total lake area (Ma et al., 2010). Qinghai Lake (36°32′-37°15′N, 99°36′-100°47′E), the largest lake in China with a surface area of 4400 km2 and an altitude of ~ 3193 m above sea level, lies in the cold and semiarid region of China's NE Qinghai–Tibet Plateau (Fig. 1). Qinghai Lake has a water volume of 7.16 × 1010 m3. The mean depth of the lake is 21 m and the maximum depth is 25.5 m (Li et al., 2007). The lake water has a salinity of 15.5 g/L and pH of 9.06. Its water chemistry is characterized by Na + N Mg2 + N K + N Ca 2 + and Cl− N SO 24 − ≈ CO 23 − N NO− 3 (Sun et al., 1991). Around the lake, the average annual air temperature is

Fig. 5. Distributions of wind field (arrows) and humidity field (colors) at 600 hPa over the Qinghai Lake Basin and adjacent regions. Units of the color scale are g/kg for humidity; the central red region is the Qinghai Lake Basin.

30

B.-L. Cui, X.-Y. Li / Science of the Total Environment 527–528 (2015) 26–37

Fig. 5 (continued).

~− 0.1 °C. The average annual precipitation is 357 mm, with more than 65% occurring in summer, but evaporation is 3 to 4 times higher than precipitation (Li et al., 2007). 2.2. Sampling Precipitation samples were collected monthly from July 2009 to June 2010 at 14 locations (P1–P14) that were distributed evenly throughout the basin (Fig. 1). The location information was acquired by GPS (global positioning system). A total of 124 samples, including 75 of rainwater and 49 of snow or sleet, were collected during the observation period. From May to October, rain samples were taken with a “collector”, composed of a polyethylene tank and a funnel, fitted a ping-pong ball to prevent evaporation of the sample once collected. From November to April,

snow and sleet samples were collected using a vat installed on the ground and then melted in an airtight container at room temperature. All precipitation samples were measured and transferred into 100-mL high-density polyethylene square bottles for isotopic analyses. During the sampling period, lake water samples were collected monthly at 5 locations (L1–L5; Fig. 1). A total of 60 lake water samples were collected. All lake water samples were taken by hand-dipping approximately 0.2 m below the lake surface and stored in 100-mL square bottles made of high-density polyethylene for isotopic analyses. The stable isotopes of precipitation and lake water were analyzed using a Picarro L1102-i water isotope analyzer, in the Stable Isotope Laboratory of the Institute of Geology and Geophysics at the Chinese Academy of Sciences, Beijing. The isotopic values were reported using the standard δ notation relative to the V-SMOW (Vienna Standard Mean Ocean

B.-L. Cui, X.-Y. Li / Science of the Total Environment 527–528 (2015) 26–37

Water) standard; the precisions were ±0.5‰ and ±0.1‰ for δ2H and δ18O, respectively. Weighted averages (δW ) were calculated for annual values of δ2H, δ18O and d-excess at each sampling location according to: δW ¼

n X i¼1

n X P i δi = Pi

ð1Þ

i¼1

where Pi is the monthly precipitation (mm) and δi is the δ2H, δ18O or dexcess value (‰). 2.3. Analytical methods We selected altitude effect (a shift from lower to higher elevation) and lake effect (from lake surface to continent, similar as continental effect) as variables to assess geographical changes in the stable isotopes

31

of precipitation in the Qinghai Lake Basin (Gat et al., 1994; Clark and Fritz, 1997). Altitude effect is a temperature-dependent phenomenon that can be explained by the rainout from adiabatic cooling (Coplen, 1993). Lake effect is represented by the relationships between the δ18O of precipitation and the distance between the sampling location and lake center (Fig. 1, Haixin Mountain), to explore the influence of evaporation from the lake on the basin's total precipitation (Gat et al., 1994; Bowen et al., 2012). In order to reveal the source of air masses and transport paths of the precipitation, and hence analyze the effect of moisture transport patterns on the content of δ18O in precipitation in the Qinghai Lake Basin, we used reanalysis data sets from NCEP–NCAR (National Centers for Environmental Prediction and National Center for Atmospheric Research, USA) to calculate the monthly wind field and humidity field for 600 hPa and precipitable water field at the surface level over the basin and adjacent regions from July 2009 to June 2010 (Kalnay et al.,

Fig. 6. Distributions of precipitable water (colors) at surface level over the Qinghai Lake Basin and adjacent regions. Units of the color scale are kg/m2; the central red region is the Qinghai Lake Basin.

32

B.-L. Cui, X.-Y. Li / Science of the Total Environment 527–528 (2015) 26–37

Fig. 6 (continued).

1996). The NCEP/NCAR data sets include monthly-averaged wind direction, wind speed, relative humidity, and precipitable water reanalysis data, with a spatial precision of 2.5° longitude–latitude grids (available at http://www.cdc.noaa.gov/cdc/reanalysis/). These procedures help to identify changes in the source regions of precipitation over the study area. A two component mixing model was used to estimate the contribution of vapor from lake evaporation to total basin precipitation (Peng et al., 2005). The method assumes that precipitation represents a mixture of two components: one derived from the lake evaporation flux, and the other from advected vapor flux (Froehlich et al., 2008; Kong et al., 2013). The mixing equation is: fc ¼

dc −dadv devap −dadv

ð2Þ

where fc is the fraction recycled from lake evaporation, dc is the d-excess of local precipitation corrected for the effect of sub-cloud evaporation,

and dadv and devap are the d-excess of advected vapor and recycled evaporated moisture, respectively (Kong et al., 2013). The devap is estimated by the Craig–Gordon model (Craig and Gordon, 1965): Revap ¼

Rl =α−hRA ð1−hÞα k

ð3Þ

where R represents the isotopic ratio (R = 1 + δ), the subscripts evap, l and A indicate evaporated moisture, lake water and atmospheric vapor, respectively, h is the relative humidity, and α and αk are the equilibrium fraction factor and kinetic fraction factor (for deuterium and oxygen18), respectively. The following values have been used for deuterium (2α or 2αk) and oxygen-18 (18α or 18αk) (Majoube, 1971; Froehlich et al., 2008): α ¼ e1:137T

−2

103 −0:4156T −1 −2:066710−3

ð4Þ

α ¼ e24:844T

−2

103 −76:248T −1 þ52:61210−3

ð5Þ

18

2

B.-L. Cui, X.-Y. Li / Science of the Total Environment 527–528 (2015) 26–37

5

a

Study area

Lanzhou

Hong Kong

Wulumuqi

Zhangye

Lasa

33

Changsha

δ18 O/‰

0 -5

-10 -15 -20 -25 1

2

3

4

5

6

7

8

9

10

11

12

Month 30

b

25

Study area

Lanzhou

Hong Kong

Wulumuqi

Zhangye

Lasa

Changsha

d-excess

20 15 10 5 0 -5 1

2

3

4

5

6

Month

7

8

9

10

11

12

Fig. 7. Seasonal variation of δ18O in precipitation (a) and the corresponding d-excess (b) in the Qinghai Lake Basin and other stations derived from GNIP network.

2

α k ¼ 1 þ 0:024  n

18

α k ¼ 1 þ 0:0289  n

ð6Þ

ð7Þ

where T is the temperature (K), and the value 0.58 was adopted for n (Stewart, 1975). Relevant monthly meteorological parameters were obtained from the Gangcha weather station, which is the nearest weather station from Qinghai Lake within the study area (Fig. 1). 3. Results and discussion 3.1. Characteristics of stable isotope of the precipitation The δ18O values ranged from −24.40 to −2.80‰ (mean −11.72‰), and the δ2H values ranged from − 180.80 to − 11.54‰ (mean −77.15‰; Fig. 2). The values fell within the ranges reported previously for China: which were − 35.5 to + 2.5‰ for δ18O and − 280.0 to + 24.0‰ for δ2H (Tian et al., 2001b). The Local Meteoric Water Line (LMWL) was defined by the δ18O and δ2H content of precipitation in the Qinghai Lake Basin (Fig. 2): δ2 H ¼ 7:86 δ18 O þ 15:01; VSMOWðn ¼ 124; R ¼ 0:99Þ : The slope of LMWL was similar to the slopes of meteoric water lines for northwestern China (7.05, Liu et al., 2008) and western China (7.56, Ma et al., 2009). All slopes were less than 8, indicating that some non-equilibrium evaporation processes occurred as raindrops fell below the cloud base (Friedman et al., 1962; Dansgaard, 1964; Araguás-Araguás et al., 1998).

The δ18O and δ2H of precipitation enriched gradually from January to July and depleted gradually from July to December (Fig. 3). According to the surface air temperature collected from the Gangcha and Tianjun weather stations (Fig. 3), δ18O and δ2H values were highly coincident with air temperature trends, with high values in the summer season and low values in the winter season, indicating that temperature effects controlled the δ18O and δ2H levels present in precipitation. The seasonal changes of δ18O and δ2H also coincided with reported levels of oxygen isotopes found in the precipitation of Delingha, Wulumuqi, Zhangye and other inland areas of central Asia (Zhang and Yao, 1995; Araguás-Araguás et al., 1998; Tian et al., 2003, 2007; Yu et al., 2008). The deuterium excess (d-excess) is defined as d = δ2H − 8 δ18O (Dansgaard, 1964), and the d-excess values of most continental waters are close to 10‰ (Craig, 1961). The inset of Fig. 2 shows the expected δ18O and δ2H values for evaporated water vapor and residual liquid water relative to the GMWL (Gat et al., 1994). The isotopic values of precipitation in the basin were plotted mostly above and to the left of the GMWL (Fig. 2), indicating that the d-excess values were greater than 10‰ due to the recycled water derived from evaporated vapor (Gat et al., 1994; Bowen et al., 2012). Values of d-excess are controlled mainly by relative humidity and temperature over the evaporating surface, and wind speed at the source region of atmospheric moisture (Merlivat and Jouzel, 1979; Rozanski et al., 1993; Froehlich et al., 2002). We found that d-excess of precipitation ranged from 4.38 to 31.10‰ (mean 16.59‰), with most values much higher than 10‰ (Fig. 4). High d-excess of precipitation has been reported in the regions around the eastern Mediterranean, Caspian and Aral Seas and the Great Lakes, due to high level of recycled moisture from large bodies of surface water or lake water mixing with the atmospheric vapor (Gat and Carmi, 1970; Aizen et al., 1996; Kattan, 1997; Kreutz et al., 2003; Gat et al., 1994; Machavaram and Krishnamurthy, 1995). Therefore,

34

B.-L. Cui, X.-Y. Li / Science of the Total Environment 527–528 (2015) 26–37 30

June

July

Table 2 Relationship between d-excess in monthly precipitation and sampling altitude from April to October.

August

d-excess/‰

25 20 15 10 5 0 3200

3300

3400

3500

3600 Altitude/m

3700

3800

3900

4000

Month

Equations

n

R2

R

P

April May June July August September October

d = 0.0008 Alt + 19.69 d = 0.0048 Alt − 0.07 d = 0.0069 Alt − 11.04 d = 0.0082 Alt − 11.73 d = 0.0123 Alt − 23.94 d = 0.0037 Alt + 1.46 d = 0.0058 Alt + 31.75

10 14 14 14 13 12 8

0.001 0.213 0.364 0.261 0.773 0.094 0.084

0.035 0.462 0.603 0.511 0.879 0.307 0.290

– – P b 0.01 P b 0.05 P b 0.001 – –

Fig. 8. Altitude effect of d-excess in monthly precipitation from June to August.

the high d-excess of precipitation in the Qinghai Lake Basin (N10‰) would be due to high amounts of recycled moisture evaporated from the lake mixing with atmospheric vapor. The ranges of d-excess values in each month (excluding December, which had only two samples) were above 10‰, with the monthly means fluctuating from 11.02‰ in October to 22.4‰ in April. These larger ranges of d-excess in precipitation indicated that the moisture sources and moisture recycle were complex in the Qinghai Lake Basin. 3.2. Altitude effect and lake effect The altitude effect of δ18O in annual precipitation was significant (Table 1) and the best-fit equation was: δ18 O ¼ ‐0:002 Alt–1:025 ðn ¼ 14; Pb0:01; R ¼ ‐0:656Þ : The equation indicated that δ18O was depleted at a rate of −0.2‰ per 100 m elevation, similar to what has been found in precipitation of the Tianshan Mountains (Pang et al., 2011) and in global precipitation (Bowen and Wilkinson, 2002). In monthly precipitation, the δ18O depleted from low altitude to high altitude regions in all months except August. The best-fit equations were significant (P b 0.02) in January, March, May and September (Table 1). Due to freezing at the surface of Qinghai Lake (Che et al., 2009) and the weak contribution of vapor from the lake to precipitation for November through March, the annual and monthly lake effect of δ18O were analyzed from April to October (Table 1). The lake effect of δ18O was significant in the annual precipitation in basin (Table 1), and the best-fit equation was: δ18 O ¼ ‐0:0116 Dis–7:65 ðn ¼ 14; Pb0:01; R ¼ 0:714Þ indicating that the δ18O of precipitation depleted at a rate of −0.0116‰/km from the lake to the land (mountain region). The δ18O of monthly precipitation depleted significantly (P b 0.05) from the lake region to the mountain region in all months except during summer (June to August), suggesting that the basin's terrain influenced precipitation distinctly in the months of April, May, September and October. The significant altitude and lake effects indicated that heavy isotopes in air masses tend to deplete progressively during rainout of moisture on its way from the lake to the mountain region, as altitude and distance increase. Combined with the high d values in the precipitation (Fig. 4), these findings suggested that the vapor evaporated from the lake would strongly influence precipitation and create a distinct regional water cycle. Thus, the contributions of evaporation to precipitation in the basin cannot be ignored. However, the altitude and lake effects on the δ18O values of precipitation were not significant in all summer months (Table 1), indicating that sources of moisture in summer precipitation were relatively complex, likely due to sub-cloud evaporation and the recycling of moisture from lake water (Dansgaard, 1964; Araguás-Araguás et al., 1998).

3.3. Sources of precipitation in the Qinghai Lake Basin The moisture in the basin and adjacent regions was derived predominantly from the WC during the period from October 2009 to May 2010 (Fig. 5). Due to a high pressure ridge centered at about 80°–90°E over the Tibetan Plateau, cold and dry air moved out of the plateau to the north, east, and south from about October through April (AraguásAraguás et al., 1998). The humidity (under 2 g/kg) and the precipitable water (under 5 kg/m2) were very low in the basin over the same period (Fig. 6), in agreement with results from Yu et al. (2008). In summer season (June to August), low pressure over the TP is centered at about 70°–80°E and induces a supply of moist, warm air from the Indian and Pacific Oceans to the continent (Araguás-Araguás et al., 1998), this results in relatively higher humidity and precipitable water in summer on the plateau (Figs. 5 and 6). From July to August, moisture in the basin was derived predominantly from the SEAM, while the SWAM did not reach the basin due to its interception by Tanggula Mountain (Figs. 5 and 1). Meanwhile, the transition in atmospheric circulation that controls the basin took place in June and September. The SEAM strengthened gradually, while the WC weakened gradually in June, and inversely in September (Gao, 1952; Ye et al., 1958). To determine more precisely the origin of moisture entering the basin, monthly variations in δ18O and d-excess of precipitation were compared with analogous values for Hong Kong and Changsha (which is southeast of the study area and affected by the SEAM), Lhasa (southwest of the study area, and affected by the SWAM in the rainy season and the WC in the dry season), Urumqi and Zhangye (northwest and north of the study area, respectively, and affected by the WC), and Lanzhou (southeast of the study area, and affected by the SEAM in the rainy season and by the WC in the dry season; Fig. 7; Araguás-Araguás et al., 1998; Ma et al., 2012). According to Fig. 7a, there is a positive relationship between δ18O and temperature at Urumqi and Zhangye, controlled by the WC, with high δ18O in summer and low δ18O in winter (Tian et al., 2007; Yao et al., 2013). More negative δ18O at Hong Kong and Changsha, affected by the SEAM (Araguás-Araguás et al., 1998), generally occur during summer and autumn, while less negative or even positive δ18O occur during winter and spring; because the moisture contributed by adjacent seas or local evaporation accounts for the main precipitation during winter and spring, while summer monsoon brings huge amounts of moisture from remote seas associated with higher temperature and larger precipitation amounts (Xie et al., 2011). Low δ18O of Lhasa observed in summer is the result of strong monsoonal activity, because vapor from the Indian Ocean moves to the southern part of the Tibetan Plateau and is uplifted onto the southern Himalayas, this uplift brings intense precipitation, resulting in heavily depleted 18O in subsequent precipitation, which affects the δ18O of precipitation at Lhasa (Tian et al., 2007). By contrast, the higher δ18O values of Lhasa concur with low precipitation amount in winter when the westerlies prevail (Tian et al., 2001a; Yao et al., 2013). Seasonal variations of δ18O in the Qinghai Lake Basin were similar to those of Wulumuqi, Zhangye, Lhasa and Lanzhou when controlled by the WC from October through May, and to those of Hong Kong and Changsha when controlled by the SEAM from June to August (Fig. 7a). In contrast, variations of δ18O

B.-L. Cui, X.-Y. Li / Science of the Total Environment 527–528 (2015) 26–37

35

Table 3 Contribution of moisture evaporated from Qinghai Lake to total basin precipitation. Time period

April

May

June

July

August

September

October

Annual

Recycling fraction (%) Contribution to precipitation (mm) Monthly precipitation (mm)

16.32 0.46 2.80

14.59 7.41 50.80

12.96 7.45 57.50

24.03 26.62 110.80

37.93 34.29 90.40

26.87 13.86 51.60

3.03 0.45 14.70

23.42 90.54 2.80

were distinctly different to those of Lhasa controlled by the SWAM from June to September (Tian et al., 2001a), and to those of Hong Kong and Changsha controlled by the SEAM from September through May (Fig. 7a). These results were consistent with the observed wind field based on the NCEP/NCAR reanalysis datasets (Fig. 5). The basin's moisture was derived predominantly from the SEAM in June to August and from the WC in September through May. Again, the basin was not influenced by the SWAM due to the presence of Tanggula Mountain. On the other hand, combined with the significant lake effect of δ18O in precipitation (Table 1), the monthly values of d-excess in precipitation in the basin were higher than those for Hong Kong, Changsha, Lanzhou, Wulumuqi and Zhangye from April to October (Fig. 7b); a likely cause would be the high amount of recycled moisture from lake water mixing with atmospheric moisture (Gat and Carmi, 1970; Aizen et al., 1996; Kattan, 1997; Kreutz et al., 2003; Gat et al., 1994; Machavaram and Krishnamurthy, 1995), suggesting that the contribution of the vapor from Qinghai Lake to water dynamics in the basin is substantial. 3.4. Contribution of the evaporation from lake to local precipitation Due to the freezing of Qinghai Lake's surface from November through March (Che et al., 2009), evaporation from the lake was estimated monthly only from April to October. To estimate the monthly contribution of recycled moisture evaporated from the lake to basin precipitation, using Eq. (2), the d-excess of evaporated moisture from the lake (devap) was calculated using Eqs. (3) to (7). The d-excess of advected moisture (dadv) was considered equal to the d-excess values of upwind precipitation at Zhangye in April, May, September and October (moisture derived predominantly from the WC) and at Lanzhou in June, July and August (moisture derived predominantly from the SEAM). The d-excess data of Zhangye and Lanzhou stations were obtained from the GNIP network (IAEA, 2006). Sub-cloud evaporation decreases the d-excess of local precipitation (dc), especially in arid areas (Froehlich et al., 2008; Kong et al., 2013). Froehlich et al. (2008) framed a model to analyze the effect of subcloud evaporation on falling raindrops and to calculate the correcting d-excess values from the corresponding δ2H and δ18O data. However, the model could not be used in this study due to the limited meteorological parameters measured in the basin, where only two weather stations exist. We found that the relationships between the d-excess value of precipitation and the altitude were significant (P b 0.05) in June, July and August, with high d-excess values in relatively higher regions and low values in lower regions (Fig. 8 and Table 2), indicating sub-cloud evaporation decreased with altitude in summer precipitation (Holko, 1994; Froehlich et al., 2008). Also, the d-excess values changed slightly above ~3700 m a.s.l. (Fig. 8), indicating that in regions above that elevation, the sub-cloud evaporation effect were nearly free in summer precipitation of the basin. These phenomena were also found in Alpine mountain regions higher than ~ 1600 m a.s.l., which were nearly free of the sub-cloud evaporation effect, with the sub-cloud evaporation lower than about 1% (Froehlich et al., 2008). Therefore, the mean values of d-excess at the three sampling locations above 3700 m a.s.l. were selected to determine the d-excess of local precipitation (dc) in June, July and August. The relationships between the d-excess value of precipitation and the altitude were not significant in April, May, September and October, and the slopes of the corresponding equations were much lower than those observed for summer precipitation (Table 2). Notably, the temperature in those four months were lower than 5 °C; these

findings all indicated that the effect of sub-cloud evaporation on the d-excess of local precipitation (dc) was negligible in April, May, September and October (Froehlich et al., 2008; Kong et al., 2013). So, we selected the mean values of d-excess of precipitation in April, May, September and October to determine the d-excess of local precipitation (dc) in each month. The results of the two component mixing model showed that the monthly contribution of evaporation from the lake to basin precipitation ranged from 3.03% in October to 37.93% in August (Table 3), with higher values observed in the summer. Based on monthly precipitation, the annual weighted contribution of evaporation was calculated to be 23.42% or 90.54 mm/year. These results indicated that there is plentiful evaporation from the lake to mix with vapor from the upwind region and increase the d-excess value of local precipitation in the basin (Froehlich et al., 2008; Xu et al., 2011; Bowen et al., 2012). The contribution of evaporation was similar to the results of previous similar studies (Table 4). The large number of lakes on the TP (Ma et al., 2010; Song et al., 2014a) clearly results in a substantial contribution of vapor from lake surfaces to atmospheric vapor in the region. An annually resolved and absolutely dated tree ring-width chronology of the northeastern Tibetan Plateau (Yang et al., 2014) that spans 4500 years showed that precipitation variability in this region is seemingly not associated with inferred changes in the intensity of the Asian monsoon over recent millennia. Also, analysis of stable isotopes in precipitation and river water samples from different locations in western China (Tian et al., 2001a) showed that the majority of precipitation on the northern TP derived from the recycling of continental moisture through summer convective processes, and that the southwest monsoon was not a direct source of precipitation over the Qinghai Lake region. Any further large-scale climate warming might be associated with an even greater moisture supply in this region (Yang et al., 2014). If so, the lake's level would rise due to increasing precipitation and runoff on the TP (Christensen et al., 2014; Song et al., 2014b); that is, the rising water level in Qinghai Lake since 2004 may be a comprehensive effect of increasing both precipitation and runoff, and changing rainfall patterns, under the unfolding scenario of global warming. 4. Conclusion Moisture on the Qinghai Lake Basin came predominantly from the SEAM in June to August and from the WC in September through May. The transition in atmospheric circulation took place in June and September: the SEAM strengthened gradually, while the WC weakened gradually in June, and inversely in September. However, the SWAM did not Table 4 Comparison of estimates from similar studies using stable isotopes for the contribution of evaporation from a surface large water body to local precipitation. Contribution (%)

Study region

Data source

20–40 5–16 10–20 16–50 28.4–31.1 10–18 23.42

Amazon Basin North American Great Lakes Kasumigaura Lake, Japan Ihorty Lake, Madagascar Nam Co Basin, Tibet, China Michigan Lake Qinghai Lake Basin, Tibet, China

Gat and Matsui (1991) Gat et al. (1994) Yamanaka and Shimizu (2007) Vallet-Coulomb et al. (2008) Xu et al. (2011) Bowen et al. (2012) This study

36

B.-L. Cui, X.-Y. Li / Science of the Total Environment 527–528 (2015) 26–37

reach the Qinghai Lake Basin due to the interception of the Tanggula Mountain. Vapor that resulted from evaporation on Qinghai Lake strongly influenced local precipitation, making the regional water cycle distinct. The monthly contribution of lake evaporation to the basin's total precipitation ranged from 3.03 to 37.93%, with an annual contribution of 23.42% or 90.54 mm, concentrated mostly in the summer season. Thus, we found that the lake evaporation makes an important contribution to atmospheric vapor on the TP. However, this estimation of the contribution is a preliminary result based on the stable isotopes in water bodies and limited meteorological data which are currently available. More data, especially field measurements of atmospheric vapor, will be required to validate the accuracy of those estimates. In summary, we demonstrated that isotopic tracers are effective tools for investigating the moisture sources of precipitation in cold and arid regions, especially those such as the TP where weather observation stations and human settlements are spare. This approach to the measurement of moisture recycling under cold and arid conditions has great potential for hydrological studies and water resources management in Central Asia. Acknowledgments The study was supported by the National Science Foundation of China (NSFC41201039, NSFC41130640) the National Key Technology R & D Program (2012BAH31B03); the Fundamental Research Funds for the Central Universities, PCSIRT (No.IRT1108); and the Project supported by State Key Laboratory of Earth Surface Processes and Resource Ecology. References Adams, S., Titus, R., Pietersen, K., Tredoux, G., Harris, C., 2001. Hydrochemical characteristics of aquifers near Sutherland in the Western Karoo, South Africa. J. Hydrol. 24, 191–203. Aizen, V., Aizen, E., Melack, J., Martma, T., 1996. Isotopic measurements of precipitation on central Asian glaciers (southeastern Tibet, northern Himalayas, central Tien Shan). J. Geophys. Res. 101 (D4), 9185–9196. An, Z.S., Colman, S.M., Zhou, W.J., Li, X.Q., Brown, E.T., Jull, A.J.T., Cai, Y.J., Huang, Y.S., Lu, X.F., Chang, H., Song, Y.G., Sun, Y.B., Xu, H., Liu, W.G., Jin, Z.D., Liu, X.D., Cheng, P., Liu, Y., Ai, L., Li, X.Z., Liu, X.J., Yan, L.B., Shi, Z.G., Wang, X.L., Wu, F., Qiang, X.K., Dong, J.B., Lu, F.Y., Xu, X.W., 2012. Interplay between the Westerlies and Asian monsoon recorded in Lake Qinghai sediments since 32 ka. Sci. Rep. 2, 619. http://dx.doi.org/10.1038/srep00619. Araguás-Araguás, L., Froehlich, K., Rozanski, K., 1998. Stable isotope composition of precipitation over southeast Asia. J. Geophys. Res. 103 (D22), 28721–28742. Bisselink, B., Dolman, A.J., 2009. Recycling of moisture in Europe: contribution of evaporation to variability in very wet and dry years. Hydrol. Earth Syst. Sci. 13, 1685–1697. Bowen, G.J., Wilkinson, B.H., 2002. Spatial distribution of δ18O in meteoric precipitation. Geology 30 (4), 315–318. Bowen, G.J., Kennedy, C.D., Henne, P.D., Zhang, T.L., 2012. Footprint of recycled water subsidies downwind of Lake Michigan. Ecosphere 3 (6), 1–16. Chang, J., Wang, G.X., 2010. Major ions chemistry of groundwater in the arid region of Zhangye Basin, northwestern China. Environ. Earth Sci. 61, 539–547. Che, T., Li, X., Jin, R., 2009. Monitoring the frozen duration of Qinghai Lake using satellite passive microwave remote sensing low frequency data. Chin. Sci. Bull. 54. http://dx. doi.org/10.1007/s11434-009-0044-3. Christensen, J.H., Kumar, K.K., Aldrian, E., 2014. Climate phenomena and their relevance for future regional climate change. In: Stocker, T.F., et al. (Eds.), Climate Change 2013: The Physical Science Basis. Working Group I Contribution to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, UK. Clark, I.D., Fritz, P., 1997. Environmental Isotopes in Hydrogeology. Lewis Publishers, New York. Coplen, T.B., 1993. Uses of environmental isotopes. In: Alley, W.M. (Ed.), Regional Groundwater Quality. Van Nostrand Reinhold, New York, pp. 227–254. Craig, H., 1961. Isotopic variation in meteoric waters. Science 133, 1702–1703. Craig, H., Gordon, L., 1965. Deuterium and Oxygen-18 variation in the ocean and the marine atmosphere. In: Tongiorgi, E. (Ed.), Proceedings of the Conference on Stable isotopes in Oceanographic studies and Paleotemperatures, pp. 9–130 (Spoleto, Italy). Dansgaard, W., 1964. Stable isotopes in precipitation. Tellus 16 (4), 436–468. Edmunds, W.M., Ma, J.Z., Aeschbach-Hertig, W., Kipferd, R., Darbyshire, D.P.F., 2006. Groundwater recharge history and hydrogeochemical evolution in the Minqin Basin, North West China. Appl. Geochem. 21, 2148–2170. Friedman, I., Machta, L., Soller, R., 1962. Water vapour exchange between a water droplet and its environment. J. Geophys. Res. 67, 2761–2766. Froehlich, K., Gibson, J.J., Aggarwal, P.K., 2002. Deuterium excess in precipitation and its climatological significance. Study of Environmental Change using Isotope Techniques. IAEA, Vienna, pp. 54–66.

Froehlich, K., Kralik, M., Papesch, W., Rank, D., Scheifinger, H., Stichler, W., 2008. Deuterium excess in precipitation of Alpine regions—moisture recycling. Isot. Environ. Health Stud. 44 (1), 61–70. Gao, Y.X., 1952. Analysis of the Westerly Cycle over the China in the winter half year by using the temperature of the troposphere. Acta Meteorologica Sinica Z1, 48–60 (in Chinese). Gat, J.R., Carmi, I., 1970. Evolution of the isotopic composition of atmospheric waters in the Mediterranean Sea area. J. Geophys. Res. 75, 3039–3048. Gat, J.R., Matsui, E., 1991. Atmospheric water balance in the Amazon Basin: an isotopic evapotranspiration model. J. Geophys. Res.-Atmos. 96, 13179–13188. Gat, J.R., Bowser, C.J., Kendall, C., 1994. The contribution of evaporation from the Great Lakes to the continental atmosphere: estimate based on stable isotope data. Geophys. Res. Lett. 21 (7), 557–560. Hao, X., 2008. A green fervor sweeps the Qinghai–Tibetan Plateau. Science 321, 633–635. Henderson, A.C.G., Holmes, J.A., Leng, M.J., 2010. Late Holocene isotope hydrology of Lake Qinghai, NE Tibetan Plateau: effective moisture variability and atmospheric circulation changes. Quat. Sci. Rev. 29, 2215–2223. Henne, P.D., Hu, F.S., Cleland, D.T., 2007. Lake-effect snow as the dominant control of mesic-forest distribution in Michigan, USA. J. Ecol. 95, 517–529. Holko, L., 1994. Stable environmental isotopes of 18O and 2H in hydrological research of mountainous catchments. J. Hydrol. Hydromech. 43, 249–274. IAEA, 2006. Isotope Hydrology Information System, The ISOHIS Database. Online at:. http://www.iaea.org/water. Jin, Z.D., Zhang, F., Wang, H.L., Bai, A.J., Qiu, X.N., 2013. The reasons of rising water level in Lake Qinghai since 2005. J. Earth Environ. 4 (3), 1355–1362. Kalnay, E., Kanamitsu, M., Kistler, R., Collins, W., Deaven, D., Gandin, L., Iredell, M., Saha, S., White, G., Woollen, J., Zhu, Y., Chelliah, M., Ebisuzaki, W., Higgins, W., Janowiak, J., Mo, K.C., Ropelewski, C., Wang, J., Leetmaa, A., Reynolds, R., Jenne, R., Joseph, D., 1996. The NCEP/NCAR 40-year reanalysis project. Bull. Am. Meteorol. Soc. 77, 437–471. Kattan, Z., 1997. Chemical and environmental isotope study of precipitation in Syria. J. Arid Environ. 35, 601–615. Kong, Y., Pang, Z., 2011. Isotope hydrograph separation in alpine catchments: a review. Sci. Cold Arid Reg. 3 (1), 86–91. Kong, Y.L., Pang, Z.H., Froehlich, K., 2013. Quantifying recycled moisture fraction in precipitation of an arid region using deuterium excess. Tellus B 65, 19251. http://dx.doi.org/ 10.3402/tellusb.v65i0.19251. Kreutz, K.J., Wake, C.P., Aizen, V.B., Cecil, L.D., Synal, H.A., 2003. Seasonal deuterium excess in a Tien Shan ice core: influence of moisture transport and recycling in Central Asia. Geophys. Res. Lett. 30 (18), 1922. http://dx.doi.org/10.1029/2003GL017896. Li, X.Y., Xu, H.Y., Sun, Y.L., Zhang, D.S., Yang, Z.P., 2007. Lake-level change and water balance analysis at Lake Qinghai, west China during recent decades. Water Resour. Manag. 21, 1505–1516. Li, X.D., Xiao, J.S., Li, F.X., Xiao, R.X., Xu, W.X., Wang, L., 2012. Remote sensing monitoring of the Qinghai Lake based on EOS /MODIS data in recent 10 years. J. Nat. Resour. 27 (11), 1962–1970 (in Chinese). Liu, J.R., Song, X.F., Yuan, G.F., Sun, X.M., Liu, X., Chen, F., Wang, Z.M., Wang, S.Q., 2008. Characteristics of δ18O in precipitation over northwest China and its water vapor sources. Acta Geograph. Sin. 63 (1), 12–22 (in Chinese). Luo, H., Yanai, M., 1984. The large-scale circulation and heat sources over the Tibetan Plateau and surrounding areas during the early summer of 1979. Part II: heat and moisture budgets. Mon. Weather Rev. 112, 966–989. LZBCAS (Lanzhou Branch of Chinese Academy of Sciences), 1994. Evolution of Recent Environment in Qinghai Lake and Its Prediction. Science Press, Beijing (in Chinese). Ma, J., Ding, Z., Edmunds, W.M., Gates, J.B., Huang, T.M., 2009. Limits to recharge of groundwater from Tibetan plateau to the Gobi desert, implications for water management in the mountain front. J. Hydrol. 364, 128–141. Ma, J.Z., Zhang, P., Zhu, G.F., Wang, Y.Q., Edmunds, W.M., Ding, Z.Y., He, J.H., 2012. The composition and distribution of chemicals and isotopes in precipitation in the Shiyang River system, northwestern China. J. Hydrol. 436–437, 92–101. Ma, R., Duan, H., Hu, C., Feng, X., Li, A., Ju, W., Jiang, J., Yang, G., 2010. A half-century of changes in China's lakes: global warming or human influence? Geophys. Res. Lett. 37, L24106. http://dx.doi.org/10.1029/2010GL045514. Machavaram, M.V., Krishnamurthy, R.V., 1995. Earth surface evaporative process: a case study from the Great Lakes region of the United States based on deuterium excess in precipitation. Geochim. Cosmochim. Acta 59 (20), 4279–4283. Majoube, M., 1971. Fractionnement en oxygène-18 et en deutérium entre léau et sa vapeur. J. Chem. Phys. 197 (10), 1423–1436. Merlivat, L., Jouzel, J., 1979. Global climatic interpretation of the deuterium-oxygen 18 relationship for precipitation. J. Geophys. Res. 84 (C8), 5029–5033. Pang, Z., Kong, Y., Froehlich, K., Huang, T., Yuan, L., Li, Z., Wang, F., 2011. Processes affecting isotopes in precipitation of an arid region. Tellus B 63 (3), 352–359. Peng, H., Mayer, B., Norman, A., Krouse, H.R., 2005. Modeling of hydrogen and oxygen isotope compositions for local precipitation. Tellus 57B, 273–282. Qin, B.Q., Huang, Q., 1998. Evaluation of the climatic change impacts on the inland lake—a case study of lake Qinhai, China. Clim. Chang. 39, 695–714. Rozanski, K., Araguás-Araguás, L., Gonfiantini, R., 1993. Isotopic patterns in modern global precipitation. Geophys. Monogr. 78, 1. Song, C.Q., Huang, B., Ke, L.H., Richards, K.S., 2014a. Seasonal and abrupt changes in the water level of closed lakes on the Tibetan Plateau and implications for climate impacts. J. Hydrol. 514, 131–144. http://dx.doi.org/10.1016/j.jhydrol.2014.04.018. Savenije, H.H.G., 1995. New definitions or moisture recycling and the relationship with land-use changes in the Sahel. J. Hydrol. 167, 57–78. Schaetzl, R.J., 2002. A spodosol-entisol transition in northern Michigan. Soil Sci. Soc. Am. J. 66, 1272–1284. Scott, R.W., Huff, F.A., 1996. Impacts of the Great Lakes on regional climate conditions. J. Great Lakes Res. 22, 845–863.

B.-L. Cui, X.-Y. Li / Science of the Total Environment 527–528 (2015) 26–37 Seneviratne, S., Corti, T., Davin, E., Hirschi, M., Jaeger, E., 2010. Investigating soil moistureclimate interactions in a changing climate: a review. Earth-Sci. Rev. 99, 125–161. Song, C., Huang, B., Richards, K., Ke, L., Phan, V.H., 2014b. Accelerated lake expansion on the Tibetan Plateau in the 2000s: induced by glacial melting or other processes? Water Resour. Res. 50. http://dx.doi.org/10.1002/2013WR014724. Stewart, M.K., 1975. Stable isotope fractionation due to evaporation and isotopic exchange of falling water drops: applications to atmospheric processes and evaporation of lakes. J. Geophys. Res. 80 (9), 1133–1146. Sun, D.P., Tang, Y., Xu, Z.Q., Han, Z., 1991. A preliminary investigation on chemical evolution of the Lake Qinghai water. Chin. Sci. Bull. 15, 1172–1174 (in Chinese). Tang, R.C., Gao, X.Q., Zhang, J., 1992. The annual changes of the water level of the Lake Qinghai in the recent thirty years. Chin. Sci. Bull. 37 (6) (524–524 (in Chinese)). Tian, L.D., Masson-Delmotte, V., Stievenard, M., Yao, T.D., Jouzel, J., 2001a. Tibetan Plateau summer monsoon northward extent revealed by measurements of water stable isotopes. J. Geophys. Res. 106, 28081–28088. Tian, L.D., Yao, T.D., Sun, W.Z., Stievenard, M., Jouzel, J., 2001b. Relationship between δD and δ18O in precipitation from north to south of the Tibetan Plateau and moisture cycling. Sci. China 44 (9), 789–796. Tian, L.D., Yao, T.D., Schuster, P.F., White, J.W.C., Ichiyanagi, K., Pendall, E., Pu, J., Yu, W.S., 2003. Oxygen-18 concentrations in recent precipitation and ice cores on the Tibetan Plateau. J. Geophys. Res. 108 (9), l–10. Tian, L.D., Yao, T.D., MacClune, K., White, J.W.C., Schilla, A., Vaughn, B., Vachon, R., Ichiyanagi, K., 2007. Stable isotopic variations in west China: a consideration of moisture sources. J. Geophys. Res. 112. http://dx.doi.org/10.1029/2006JD007718 (No. D10112). Trenberth, K.E., 1999. Atmospheric moisture recycling: role of advection and local precipitation. J. Clim. 12, 1368–1381. Trenberth, K.E., Dai, A., Rasmussen, R.M., Parsons, D.B., 2003. The changing character of precipitation. Bull. Amer. Meteor. Soc. 84, 1207–1217. Vallet-Coulomb, C., Gasse, F., Sonzogni, C., 2008. Seasonal evolution of the isotopic composition of atmospheric water vapour above a tropical lake: deuterium excess and implication for water recyling. Geochim. Cosmochim. Acta 72, 4661–4674. Wang, B.J., Huang, Y.X., He, J.H., Wang, L.J., 2004. Relation between vapour transportation in the period of East Asian summer monsoon and drought in Northwest China. Plateau Meteorol. 23 (6), 912–918 (in Chinese). Wang, B.J., Huang, Y.X., Tao, J.H., Li, D.L., Wang, P.X., 2006. Regional features and variations of water vapor in Northwest China. J. Glaciol. Geocryol. 28 (1), 15–21 (in Chinese).

37

Wang, Y.N., Zhang, B., Chen, L.X., He, J.H., Li, W., Chen, H., 2008. Relationship between the atmospheric heat source over Tibetan Plateau and atmospheric heat source and general circulation over East Asia. Chin. Sci. Bull. 53 (21), 3387–3394. Xie, L.H., Wei, G.J., Deng, W.F., Zhao, X.L., 2011. Daily δ18O and δD of precipitations from 2007 to 2009 in Guangzhou, South China: implications for changes of moisture sources. J. Hydrol. 400, 477–489. Xu, H., Hou, Z.H., Ai, L., Tan, L.C., 2007. Precipitation at Lake Qinghai, NE Qinghai–Tibet Plateau, and its relation to Asian summer monsoons on decadal/interdecadal scales during the past 500 years. Palaeogeogr. Palaeoclimatol. Palaeoecol. 254, 541–549. Xu, Y.W., Kang, S.C., Zhang, Y.L., Zhang, Y.J., 2011. A method for estimating the contribution of evaporative vapor from Nam Co to local atmospheric vapor based on stable isotopes of water bodies. Chin. Sci. Bull. 56 (14), 1511–1517. http://dx.doi.org/10. 1007/s11434-011-4467-2. Yamanaka, T., Shimizu, R., 2007. Spatial distribution of deuterium in atmospheric water vapor: diagnosing sources and the mixing of atmospheric moisture. Geochim. Cosmochim. Acta 71, 3162–3169. Yanai, M., Li, C., Song, Z., 1992. Seasonal heating of the Tibetan Plateau and its effects on the evolution of the Asian summer monsoon. J. Meteorol. Soc. Jpn 70, 319–351. Yang, B., Qin, C., Wang, J.L., He, M.H., Melvin, T.M., Osborn, T.J., Briffa, K.R., 2014. A 3,500year tree-ring record of annual precipitation on the northeastern Tibetan Plateau. PNAS 111 (8), 2903–2908. Yao, T., Masson-Delmotte, V., Gao, J., Yu, W., Yang, X., Risi, C., Sturm, C., Werner, M., Zhao, H., He, Y., Ren, W., Tian, L., Shi, C., Hou, S., 2013. A review of climatic controls on δ18O in precipitation over the Tibetan Plateau: observations and simulations. Rev. Geophys. 51, 525–548. Ye, D.Z., Tao, S.Y., Li, M.C., 1958. The mutation phenomenon of the atmospheric circulation in June and October. Acta Meteorologica Sinica 29 (4), 249–263 (in Chinese). Yu, W.S., Yao, T.D., Tian, L.D., Ma, Y.M., Ichiyanagi, K., Wang, Y., Sun, W.Z., 2008. Relationships between δ18O in precipitation and air temperature and moisture origin on a south–north transect of the Tibetan Plateau. Atmos. Res. 87, 158–169. Zhang, X.P., Yao, T.D., 1995. Relations between weather systems affecting Tibetan Plateau and oxygen isotope in precipitation. J. Glaciol. Geocryol. 17 (2), 125–131 (in Chinese). Zhang, G., Xie, H., Duan, S., Tian, M., Yi, D., 2011. Water level variation of Lake Qinghai from satellite and in situ measurement under climate change. J. Appl. Remote. Sens. 5. http://dx.doi.org/10.1117/1.3601363.