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Quaternary International xxx (2014) 1e7

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Quaternary International

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Changes of the three holy lakes in recent years and quantitativeanalysis of the influencing factors

Long Li a,*, Jing Li a, Xiaojun Yao a,b, Jing Luo a, Yongsheng Huang a, Yaya Feng a

aCollege of Geography and Environment Sciences, Northwest Normal University, 967 Anning East Road, Lanzhou 730070, Chinab State Key Laboratory of Cryosphere Sciences, Cold and Arid Regions Environmental and Engineering Research Institute, CAS, Lanzhou 730000, China

a r t i c l e i n f o

Article history:Available online xxx

Keywords:Lake water balanceLake variationThe three holy lakesTibetan Plateau

* Corresponding author.E-mail address: [email protected] (L. Li).

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a b s t r a c t

Namco Lake, Yamzho Yumco Lake, and Mapam Yamco Lake are the “three holy lakes” of Tibet. Based onthe topographic map of 1970 and the Landsat TM/ETM þ remote sensing images of 1970 and from 1990to 2012, satellite altimetry data, observed data from meteorological stations, and the changes of the“three holy lakes” in area, water level and water storage, the lake status and causes of the changes havebeen analyzed in a comparative manner. From 1970 to 2012, Namco Lake rapidly expanded in area,Yamzho Yumco Lake sharply declined, and Mapam Yamco Lake showed a slight decline with no greatchanges. The increase in precipitation was the main reason for the expansion of Namco Lake from 1970 to1998, but the increase in glacial meltwater caused by temperature rise, and the decrease in evaporationfrom the lake surface, are the main reasons for the expansion and water storage increase of Namco Lakeafter 1998. Yamzho Yumco Lake significantly expanded from 1991 to 2004 mainly because the evapo-ration was limited, and shrank after 2004 because of the decrease in precipitation and the increase inevaporation. Mapam Yamco Lake was shrinking due to higher evaporation and lower precipitation. Inaddition to glacier meltwater, there are other forms of supply, such as groundwater, wetlands, andpermafrost ablation.

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1. Introduction

As an important part of the land hydrosphere, the change of thewaters in a lake is the comprehensive results of the water balancewithin its river basin (Ding et al., 2006), and it is also a sensitiveindicator of climate change (Lu et al., 2005). The lake area ofQinghaieTibet Plateau is such an area of plateau lake groups that ishighest in elevation, most in number and largest in area around theworld (Ma et al., 2011). In recent years, the overall temperature onQinghaieTibet Plateau has increased (Wu et al., 2005; Holmes et al.,2009). With certain differences in spatial precipitation change,most areas have showed a trend of humidifying except easternTibet (Jiang et al., 2012). Since the 1980s, the glacial meltwater hasincreased as glaciers on the Plateau have retreated quickly (Shiet al., 2006). Influenced by these and other conditions, the num-ber of lakes on the Plateau has increased, and the total areaexpanded. The southwest showed little change while the northeastshowed expansion (Yan and Qi, 2012). The strong contraction orexpansion of lakes has exerted a huge impact on natural

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environment and human life, and thus it has been attracting moreand more attention (Shi, 1990; Yin et al., 2013).

Namco Lake, Yamzho Yumco Lake and Mapam Yamco Lake arecalled the “three holy lakes” of Tibet. They are the sites of thetraditional “Lake Visiting Festival” of the Tibetan people and thegrassland around them is a good natural pasture. Therefore,changes of the “three holy lakes” have been drawing people’sattention. Under the background of climate warming, manyscholars have carried out scientific research on Namco Lake,Yamzho Yumco Lake, and Mapam Yamco Lake in recent years. Forexample, Zhu et al. (2010) calculated the changes in the watervolume of Namco Lake from 1970 to 2004, and found that both thearea and the water volume showed a trend of increase in the past34 years, accelerating from 1992 to 2004. Zhang et al. (2011) foundthat the water volume in Namco Lake increased by114.214 � 108 m3 from 1976 to 2009 using GLAS altimeter andmeasured data. Liu (1995) analyzed the variation in the water levelof Yamzho Yumco Lake systematically and showed that the waterlevel of the lake was slowly falling from 4441.04�m in 1974e4438.44�m in 1992 in this period. Chu et al. (2012) extended thetime series of the lake’s water level to 2009 and found that thewater level of the lake had risen from 1996 to 2004, but it had

es in recent years and quantitative analysis of the influencing factors,4.051

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L. Li et al. / Quaternary International xxx (2014) 1e72

dropped significantly after 2004. La et al. (2012) used the topo-graphic map and Landsat TM remote sensing images determinethat the area of the lake had reduced by 1.56 km2 from 1975 to2009. At present, scholars hold different views about the causesthat have led to the changes of Namco Lake, Yamzho Yumco Lake,and Mapam Yamco Lake. Ma et al. (2012) believe that the increasein precipitation is the main cause of the expansion of Namco Lake.Zhu et al. (2010) andWu and Zhu (2008) think that the expansion ismainly caused by the increase in glacial meltwater due to climatechange. Chu et al. (2012) think the fluctuation of annual precipi-tation in Yamzho Yumco Lake is the main influential factor thatmade the water level of the lake change, and human activities(Yamzho Yumco Lake Hydropower Pumped Storage Project Station)had no significant effect on the water level of the lake. Bian et al.(2009) think that the main cause of lake changes is that the tem-perature rise caused lake evaporation to exceed the increase inprecipitation, and the operation of Yang Lake Hydroelectric Stationmade the water level of the lake go up slightly.

As for the causes that have led to the decrease in the watervolume ofMapam Yamco Lake, Ye et al. (2008) think that changes inthe temperature and precipitation of the basin had an effect. Laet al. (2012) believe that the main cause is the decrease in basinprecipitation and a non-significant increase in evaporation capacityas well as snow and glacier melting as secondary reasons.

Therefore, in order to differentiate the changing processesaffecting Namco Lake, Yamzho Yumco Lake, and Mapam YamcoLake, the parameters of each lake at different time periods weredetermined, and each element influencing the water volume ofeach lake was calculated. Remote sensing (RS), GIS, and mathe-matical statistics have been comprehensively used in this paper.This paper provides a reference for understanding the changes andtheir influences on the “three holy lakes” in Tibet by analyzing theprocesses and calculating the water balances of the three lakes.

2. Study area

Namco Lake (30�300w30�560N, 90�160w91�030E), YamzhoYumco Lake (28�160w29�110N, 90�210w91�050E) and MapamYamco Lake (30�340w30�470N, 81�220w81�270E) are called the“three holy lakes” of Tibet. Namco is located northwest of theNyenchen thanglha Mountains and stretches across two counties,Baingoin and Damxung. Yamzho Yumco Lake and Mapam YamcoLake lie between the Himalayas and Gangdisê Mountains, and arewithin Nagarze County and Burang County respectively (Fig. 1).

Namco Lake is also known as Tengri Nor, which means “heav-enly lake” in the Tibetan language. It was formed by tectonic

Fig. 1. Location of Namco Lake, Yamzho Y

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depression resulting from the Himalayamovement (Wang and Dou,1998). Its surface is at an altitude of 4,718�m and it covers an area of1,920 km2. It is the second largest plateau lake of the QinghaieTibetPlateau, ranking second only to Selinco Lake (Bian et al., 2010).Namco Lake is a bicarbonate sodium freshwater-slightly salt waterlake, whose water supply is mainly from surface runoff and pre-cipitation from the lake surface. Its catchment covers an area of2196.23 km2, and extensive modern glaciers are present in theNyenchen thanglha Mountains to the southeast (Kropácek et al.,2012).

Yamzho Yumco Lake, “Jasper Lake” in the Tibetan language, hadbeen an exorheic lake in history and retreated into an inland lakelater as the climate became dry. It is a brackish lake, 130 km longfrom east towest, and 70 kmwide from north to south. Its surface isat an altitude of 4,440�m, forming a fall of 840�m with the Brah-maputra on the northern side, and thus it is rich in hydropowerresources. It lies in the southern Tibetan mountainous scrubgrassland semi-arid climate. Its catchment area is 6100 km2. It ismainly supplied by surface runoff, with ice and snow meltwateraccounting for about 16% of the total supply (Wang and Dou, 1998).

Mapam Yamco Lake means “all-powerful holy lake” in the Ti-betan language. Its surface is at an elevation of 4,586�m. It liesbetween Naimonnanyi on the southern side and Mount Kan-grinboqe on the northern side (Owen et al., 2010). It is one of thelargest high altitude lakes in the world (Wang and Dou, 1998). It isunder the plateau subfrigid zone drought climate. Its catchmentbasin area is 4,148 km2 and its supply mainly depends on rainfalland surface runoff (Guan et al., 1984).

3. Data and methods

3.1. Data sources

In order to obtain the data on changes of Namco Lake, YamzhoYumco Lake and Mapam Yamco Lake in the past 40 years, 331:50,000 topographic maps, 22 1:100,000 topographic maps whichhad been made by the State Bureau of Surveying and Mapping ofHeadquarters of the General Staff of the Chinese People’s LiberationArmy in the 1970s, have been collected in total. These maps basi-cally reflect the status of the lakes in the 1970s. USGS/NASA (http://earthexplorer.usgs.gov) provided 71 Landsat TM/ETM þ remote-sensing images with a spatial resolution of 30�m, shown in Table 1.In addition to using the data on the water level of the three lakesfrom the existing literature, ICESAT height measurement satellitedata (http://nsidc.org/data) has been used to obtain water leveldata from 2003 to 2009. In addition, an SRTM Digital Elevation

umco Lake and Mapam Yamco Lake.


http://earthexplorer.usgs.gov

http://earthexplorer.usgs.gov

http://nsidc.org/data

L. Li et al. / Quaternary International xxx (2014) 1e7 3

Model with a spatial resolution of 90�m provided by the Consul-tative Group for International Agricultural Research (CGIAR)-Coa-lition of Spatial Information (CGIAR-CSI) was used. Data of theglacier changes of each lake basin was provided by the ProjectGroup of “A Survey on Glacier Resources in China and TheirChanges”, a groundwork special project of the Ministry of Scienceand Technology.

Table 1Landsat TM/ETM þ Remote Sensing Images. *Landsat TM; otherwise Landsat ETMþ.

Path/Row Acquisition time

138/039 1989-09-17*; 1992-12-13*; 1998-09-17*; 1999-10-30;2000-11-17; 2001-06-132001-11-26; 2002-02-24; 2002-10-30; 2003-11-26;2003-12-20*; 2004-09-17*2004-10-19*; 2005-09-20*; 2005-11-07*; 2006-10-09*;2007-05-05*; 2007-09-282008-07-15*; 2008-10-06; 2008-12-17*; 2009-10-25;2009-11-02*; 2010-04-27*2010-09-26; 2011-09-05*; 2011-10-07*; 2012-10-01;2012-10-17; 2012-11-18

138/040 1989-01-19*; 1998-09-17*; 1999-10-30; 2000-09-30;2001-10-19; 2001-11-042002-11-07; 2002-12-09; 2003-11-10; 2003-12-04*;2004-09-17*; 2004-12-22*2005-11-23*; 2006-10-17; 2006-12-20; 2007-05-01*;2007-10-20; 2008-01-16*2008-10-22; 2009-10-17*; 2010-04-11*; 2010-09-26;2011-10-15; 2012-10-17

144/039 1990-04-07*; 1998-11-01*; 1999-11-09; 2000-10-10;2001-08-26; 2002-09-302003-10-03; 2004-11-06; 2005-10-24; 2006-10-11;2007-10-30; 2008-11-012009-10-27*; 2009-11-28*; 2010-10-26*; 2011-10-01*;2012-10-11

The meteorological stations closest to the lakes have been usedas the reference for the climate background: Nagqu, Baingoin,Xainza and Damxung meteorological stations for Namco Lake;Nagarze meteorological station for Yamzho Yumco Lake; and Bur-ang meteorological station for Mapam Yamco Lake. The dataobserved includes daily precipitation, daily average temperature,daily minimum temperature, daily maximum temperature, windspeed, sunshine duration, vapor pressure, and other parameterswithin the research period. Due to the complexity of the terrain andclimate, 0.5� interpolation data has been used as the supplemen-tary data for temperature and precipitation. All the above datawereobtained from the China meteorological science data sharing ser-vice network (http://cdc.cma.gov.cn).

3.2. Information on lake changes

3.2.1. Area parametersIn order to obtain the area parameters of Namco Lake, Yamzho

Yumco Lake, and Mapam Yamco Lake in different periods, topo-graphic maps and remote sensing images were processed withdigital and visual interpretation technologies. The processing forthe topographic maps mainly includes topographic map scanning,registering, visual interpretation and digitization. In registration, akm network was used as the control. GausseKruger projection wasuniformly employed in projection, and digital accuracy wascontrolled within one pixel. The final vector data generated wasconverted into an Albers orthoaxis equivalent double-standardparallel secant conic projection. Lake border interpretation stan-dards referred to the Project Group of, “A Survey on the Waterquality, Volume and Biological Resources of Lakes in China”


groundwork special project of science and technology (Ma et al.,2011). Remote sensing images were processed with band combi-nation and false color composition using ArcGIS 9.3. A screen digitalmethod was adopted to obtain the boundary vector data of thethree lakes, and digital accuracy was controlled within one pixel.“Calculate Geometry”, provided by ArcGIS 9.3, was used to calculatethe areas of the “three holy lakes” in different periods.

3.2.2. Water levelsThe data on water level of Namco Lake, Yamzho Yumco Lake,

and Mapam Yamco Lake originated from the literature and heightmeasurement data of ICESAT GLAS. The documentation (Lei et al.,2013) recorded the changes of Namco Lake in water level from1975 to 2010 in detail. Liu (1995) recorded the data of YamzhoYumco Lake water level from 1912 to 1992, and Chu et al. (2012)extended the record of water level to 2009. The GLAS height-measurement data from the ICESAT satellite was used to estimatethe changes of water level (Wu et al., 2012; Wang et al., 2013).According to the principle of satellite altimetry data, the water levelof a lake can be obtained by Formula (1).

HL ¼ HS � Halt � Herr (1)

Where HL is lake level (m); HS is ICESat-GLAS ellipsoid high of thealtimeter barycenter (m); Halt is measured distance by altimeter(m); and Herr is all the error correction. As the area of inland lakes isrelatively small, tides and inverse air pressure have a smallerimpact on them compared with the oceans. Therefore, the influ-ence of these errors was not considered in this study.

3.2.3. Calculation of water volumeThe calculation of lake water volume adopted the model for

lakes of the Qinghai-Tibet Plateau proposed by Song et al. (2013).The calculation method is as shown in Formula (2).

DWi ¼ZSiSi�1

ZHi

Hi�1

dSdH ¼ Si�1 þ Si2

*ðHi � Hi�1Þ (2)

Where i and i-1 is study times (year), DWi is mean annual change oflake level (km3), Si and Si-1 is lake area (km2),Hi andHi-1 is lake level(km).

3.2.4. Calculation of lake catchment areaWith SRTM-based data as the terrain data, the Hydrology model

provided by ArcGIS 9.3 was used to extract the catchment. This wascompared in Google Earth for verification to ensure that theextracted river basin scope is in conformity with the actual char-acteristics of the lakes.

3.3. Calculation of lake water balance

The “three holy lakes” in Tibet are closed inland lakes. The majorfactors that affect their water balance are surface runoff, precipi-tation, and evaporation from the lake surface. Referring to theresearch results of (Zhu et al., 2010) on Namco Lake, the waterbalance equation of the three lakes can be represented by Formula(3).

DH ¼ P þ Rs þ Rg � E � 3 (3)

Where DH is mean annual change of lake level (mm); P is meanannual precipitation on lake water zone (mm); Rs is mean annualsurface runoff depth derived from precipitation (mm); Rg is meanannual glacier melting water inflow into the lake (mm); E is mean


http://cdc.cma.gov.cn


annual evaporation from lake surface (mm); and � 3is combinedwith groundwater inflow or outflow and errors (mm).

3.3.1. Calculation of lake surface evaporationWith rugged terrain and sparse population, there are few

meteorological stations in the study area. Here, the potentialevapotranspiration within the lake basin was used to replace theevaporation on the lake. PenmaneMonteith model (Allen et al.,1998) was used and the calculation formula is shown in Formula(4).

ET0 ¼ 0:408DðRn � GÞ þ g 900Tþ273U2ðes � edÞ

Dþ gð1þ 0:34U2Þ(4)

Where ET0 is potential evapotranspiration; D is the slope of satu-ration vapor pressure curvewhen temperature reaches T (kPa�C�1);Rn is net solar radiation of the coronal layer (MJ�m2�d�1); G is soilheat flux (MJ�m2�d�1); g is dry and wet constant (kPa�C�1); T ismeanmonthly temperature (C); U2 is wind speed at the twometershigh above ground (m/s), es and ed are saturation vapor pressureand actual vapor pressure, respectively (kPa).

3.3.2. Estimation of lake precipitationThe 0.5� interpolated precipitation was used as the reference of

the precipitation on the lake. Lake precipitation was calculatedaccording to the bounding data strictly.

3.3.3. Estimation of runoff generated by precipitationAssuming that, excepting evaporation, all the precipitation on

the land surface is supplied to the lakes, the lake-surface runofffrom precipitation into the lakes can be approximately expressed asFormula (5).

RS ¼ PL � EL (5)

Here RS is runoff depth generated by precipitation (mm); PL isprecipitation on land surface (mm); EL is actual evaporation on landsurface (mm). This can be calculated with the Fu Baopu method(Qian and Li, 1996), shown in Formula (6).

EL ¼ Em

"PLEm

� 13

�PLEm

�3#

(6)

Here EL is actual evaporation on land surface (mm), Em isevapotranspiration on land surface (mm), and PL is Precipitation onland surface (mm).

3.3.4. Estimation of glacier meltwater volumeAccording to the two sets of data provided by the Project Group

of “A Survey on Glacier Resources in China and their Changes (Chinaglacier inventory project)” for the groundwork special project ofthe Ministry of Science and Technology, and as the data of theintervening years is unavailable, this paper referred to the studydata of Wang et al. (2012), Wang (2006), and Guo et al. (2007), aswell as other researchers, and then calculated the data on the areachange of the glaciers within the three lakes’ basins. The calculationis shown in Formula (7):

Ai ¼ ð1� DÞ*Ai�1 (7)

Where Ai is the area of the glaciers in the year; D is the change rateof the glaciers; and Ai�1 is the area of the glaciers in the previousyear.

Data about changes in area and glacier storage capacity of 253glaciers in the Namco Lake basin, 98 glaciers in Yamzho Yumco Lake


basin, and 241 glaciers in Mapam Yamco Lake basin, was obtainedusing the following formulas (Yao et al., 2012):

H ¼ �11:32þ 53:21 F0:3g (8)

H ¼ 34:4F0:45g (9)

Where H is mean thickness of glacier (m), Fg is glacier area (km2).Equation (8) is applicable for cirque, valley, and cirque-valley gla-ciers, but (9) is applicable for hanging glaciers. After determiningthe mean thickness, glacier storage capacity can be obtained byFormula (10):

Vg ¼ Fg*H�1000 (10)

Where Vg is glacier storage capacity (km3); and Fg is glacier area.This paper verified the uncertainty of using the empirical model

to estimate the changes in glacier volume. In the Namco basin,Zhadang Glacier had decreased by 3.180 km3 in total from 2005 to2008, an annual decrease of 1.06 km3 (Yu et al., 2013). With theempirical model, the glacier volume of Zhadang Glacier in theNamcobasinhaddecreasedby2.832km3 in total from2005 to2008,an annual decrease of 0.944 km3 on average, an error of 10.94%.Therefore, it was considered feasible to use the empirical model toestimate changes in glacier volume. The differences between typicalglaciers and basin glaciers in material balance as well as the un-certainty of the watershed hydrological model within the basinwere not taken into account (Shen et al., 2003; Wang et al., 2011).

4. Results and discussion

4.1. Changes in area of the lakes

Great changes had taken place in the area of the “three holylakes” of Tibet from 1970 to 2012 (Fig. 2). In general, Namco Lakeshowed a trend of rapid expansion, inwhich the area had increasedfrom 1943.35 km2 to 2025.05 km2 at a growth rate of 1.95�km2�y�1.Expansion accelerated from 1998 to 2012 at a rate of 3.34�km2�y�1.In contrast to Namco Lake, Yamzho Yumco Lake showed a sharpshrinking trend in which the area decreased from 643.25 km2 to557.42 km2 at a rate of 2.04�km2�y�1. Rapid shrinkage of YamzhoYumco Lake occurred in two periods, from 1970 to 1990 and from2004 to 2012, at rates of 2.70 km2 y�1 and �0.58�km2�y�1

respectively. The area increased at a rate of 4.30�km2�y�1 from1998 to 2004. Mapam Yamco Lake revealed a mild decline with nogreat changes, during which the area had decreased from417.00 km2 to 412.56 km2 at a rate of 0.11�km2�y�1, with variationsin some years. For example, the area shrank suddenly in 1999, 2005,and 2009, and especially in 2009 it declined to theminimumwithinthe scope of this study, 410.01 km2. It increased rapidly in 2000,2006 and 2010 to 414.28 km2, 413.27 km2 and 412.46 km2

respectively. The sensing image data was from October andNovember during which lakes are relatively stable. These high-digital-accuracy data show that the area of Mapam Yamco Lakefluctuated.

4.2. Changes in water storage of the three lakes

From the GLAS data in Fig. 3 showing the changes in waterstorage of the “three holy lakes” of Tibet in recent years, significantchanges had taken place in the water storage of the three lakes,especially in Namco Lake and Yamzho Yumco Lake. Comparison ofFig. 3 with Fig. 2 shows that the trend of water storage change andthat of area change are consistent. Thewater storage in Namco Lake


Fig. 2. Changes in surface areas of Namco Lake, Yamzho Yumco Lake and Mapam Yamco Lake from 1970 to 2012.

Fig. 3. Changes in Water Storage of the Namco Lake, Yamzho Yumco Lake and Mapam Yamco Lake in Recent Years by GLAS data.


increased rapidly from 2003 to 2006, a total increase of 2.420 km3,and after a slight decline in 2007 it increased slowly after 2008(Zhang et al., 2011). The water storage of Yamzho Yumco Lake haddecreased by 0.044 km3 in total from 2003 to 2009 and showed atrend of decline with fluctuations.

4.3. Calculation of water balance

In order to reveal the causes that had led to the changes of the“three holy lakes”, an analysis from the perspective ofwater balancewas done to calculate precipitation on the lake, precipitation on theland surface, glacier meltwater, evaporation from the lake surface,and variation of water storage in the lake (Table 2). The annualaverage precipitation on the lake and the annual average precipi-tation on the land surface of Namco Lake accounted for 45.11% and18.20% respectively of the total annual average supply from 1970 to2012. Therefore, the total contribution rate from precipitation was

Table 2Water Balance and Elements of Changes of Namco Lake, Yamzho Yumco Lake and Mapa

Lake Period Water quantityvariation (DH)

Precipitation onthe lake (P)

Runof

Namco 1970e1998 0.188 0.763 0.27110.82% 43.90% 15.59%

1998e2012 0.441 0.814 0.27222.65% 41.81% 13.97%

1970e2012 0.272 0.825 0.33314.87% 45.11% 18.20%

Yamzho Yumco 1991e2004 0.007 0.226 0.1971.54% 49.56% 43.20%

2004e2012 �0.024 0.243 0.1595.24% 53.05% 34.72%

1991e2012 �0.005 0.213 0.1861.11% 47.44% 41.42%

Mapam Yamco 1970e1998 �0.002 0.094 0.0350.53% 24.93% 9.28%

1998e2012 �0.001 0.088 0.0300.27% 23.78% 8.11%

1970e2012 �0.002 0.091 0.0340.54% 24.40% 9.11%


63.31%, which shows that precipitation dominated its supply. Inaddition, glacier meltwater was also an important form of supply,accounting for 35.87%, and the evaporation on the lake accountedfor 85.13%. From the perspective of water balance, 14.87% was theincrease of the lake. Comparing the period from 1970 to 1998 withthe period from1998 to 2012, both the precipitation on the lake andthe precipitation runoff on the land surface of the later period weremore than that of the former period, but the contribution fromprecipitation declined. In the second period, glacier meltwater was0.838�km3�y�1, accounting for 43.04% of the total supply, an in-crease of 10% comparedwith the contribution rate of thefirst period.The evaporation on the lake of the second period was slightly lessthan that of the first period, a decrease of 10% in the total supply.Thus, the water storage of the lake had increased by about 20%,which shows that the expansion of Namco Lake from 1998 to 2012was causedmainly by the increase of glaciermeltwater produced bytemperature rise, and the decrease of evaporation.

m Yamco Lake (DH¼PþRsþRg�E� 3).

f (Rs) Glacier meltingwater (Rg)

Evaporationfrom the lake (E)

Othersupply ( 3)

Total supply(E�þ�DH)

0.584 1.550 0.120 1.73833.60% 89.18% 6.91% 100.00%0.838 1.506 0.023 1.947

43.04% 77.35% 1.18% 100.00%0.656 1.557 0.015 1.829

35.87% 85.13% 0.82% 100.00%0.031 0.449 0.002 0.4566.80% 98.46% 0.44% 100.00%0.054 0.482 0.002 0.458

11.79% 105.24% 0.44% 100.00%0.040 0.454 0.010 0.4498.91% 101.11% 2.23% 100.00%0.125 0.379 0.123 0.377

33.16% 100.53% 32.63% 100.00%0.140 0.371 0.112 0.370

37.84% 100.27% 30.27% 100.00%0.130 0.375 0.118 0.373

34.85% 100.54% 31.64% 100.00%



The calculation for the water balance of Yamzho Yumco Lake isrestricted by the limited meteorological data. The annual averageprecipitation on the lake and the annual average precipitation onthe land surface of Yamzho Yumco Lake accounted for 47.44% and41.42% respectively of the total annual average supply from 1991 to2012. Therefore, the supply from precipitation was 88.86%, whichshows that precipitation was the primary factor that had given riseto the changes in water storage. Glacier melting water accountedfor 8.91% of the total supply, and the evaporation on the lakeaccounted for 10.11%. From the perspective of water balance, 1.11%was the amount of decrease of the lake. Compared with the periodfrom 1991 to 2004, precipitation on the lake during the period from2004 to 2012 was greater, the precipitation on the land surface wasless, and the total precipitation supply decreased by 4.99%. Thecontribution rate of the glacier melting water of the lake of thesecond period increased by 4.99% compared with the first period,equaling the contribution rate of precipitation. Evaporation on thelake in the second period increased more significantly than in thefirst period, 6.78% of the total supply, resulting in a reduction of lakewater storage. The decrease of precipitation and the increase ofevaporation was the major cause of shrinkage of Yamzho YumcoLake from 2004 to 2012.

All factors concerning water balance of Mapam Yamco Lakechanged from 1970 to 2012, but they differed in proportion. Theprecipitation on the lake and the precipitation on the land surfaceaccounted for 24.40% and 9.11% respectively of the total supply,from which the supply from precipitation accounted for 33.51%.The supply from glacier meltwater was 34.85%; and the evapora-tion on the lake was 100.54% of the total supply. Precipitation andglacier meltwater constituted the supply of Mapam Yamco Lake,accounting for 68.36% of the total supply. The difference betweenevaporation on the lake and total supply, 0.54%, was the amount ofreduction. Comparing the period from 1970 to 1998 with theperiod from 1998 to 2012, the supply from precipitation in the firstperiod was less than that in the second period on Mapam YamcoLake, a decrease of 2.32% in the total supply. The supply fromglacier meltwater increased relatively significantly, an increase of4.68% in the total supply. The percentage of evaporation slightlydeclined, by 0.26%. The rate at which the water storage decreasedmore slowly in the second period than in the first period, from0.002�km3�y�1 to 0.001 km3�y�1 on average. Despite a decrease inprecipitation from 1998 to 2012, the increase in the supply fromglacier meltwater was slightly in excess of the decrease in thesupply from precipitation. Evaporation on the lake also decreasedbut it always exceeded the total supply, and as a result the lakeshowed slow shrinkage in recent years. From the perspective ofwater balance, without taking other errors into consideration,31.64% of the supply came in other forms. Wetland and permafrostmelting in the basin was probably one of the reasons (Xu et al.,2010). In addition, there are more than 10 rivers in the basin,which are mainly supplied by snowmelt and groundwater (Laet al., 2012). The surface of Mapam Yamco Lake is at a higherelevation compared with La’ngaco Lake on its west and has waterchannel connections. Therefore, the decrease had probably flowedinto La’ngaco Lake (Taft et al., 2013).

5. Conclusions

The “three holy lakes” in Tibet have changed significantly in thepast 40 years. Namco Lake showed a trend of rapid expansion,mainly from 1970 to 2007, and its area increased at a lower rateafter 2008. Yamzho Yumco Lake showed sharp shrinkage from 1970to 1990, and after a slow expansion from 1990 to 2004 it wassteadily shrinking from 2004 to 2012. Mapam Yamco Lake showeda slow declining trend. Although it expanded in a fluctuating


manner in individual years, it has a declining trend compared with1970.

Changes that had taken place in the “three holy lakes” areclosely related to glacier meltwater runoff, precipitation, andevaporation, which played different roles. (1) Precipitation was themain supply source of Namco Lake from 1998 to 2012 and itscontribution rate was generally the same as during 1970e1998. Thecontribution rate of glacier meltwater supply increased, andevaporation accounted for a smaller percent in the total supply.From 1998 to 2012, the increase in glacier meltwater due to tem-perature rise and the decrease in evaporation on the lake were themain reasons for its expansion. (2) Precipitation and evaporationrestricted the changes of Yamzho Yumco Lake. Due to lesserevaporation in this period, the lake showed a significant expansionfrom 1991 to 2004. With an increase in precipitation after 2004,glacier meltwater increased, but the increase was not enough tooffset the increased evaporation. Therefore, the decrease in pre-cipitation together with the increase evaporation contributed tothe shrinkage of Yamzho Yumco Lake. (3) Mapam Yamco Lakeshowed an overall shrinkage from 1970 to 2012, but at a lower ratefrom 1998 to 2012. Although glacier meltwater increased andevaporationwas reduced slightly in this period, it was not sufficientto offset the precipitation decrease. There should be other forms ofsupply such as groundwater, wetlands, and permafrost.

Acknowledgements

This research was supported by the National Natural ScienceFoundation of China (41261016), Gansu Province Natural ScienceFoundation (1308RJZA141).

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