Study on the changes of water cycle and its impacts in the source region of the Yellow River

142Science in China Ser. E Engineering & Materials Science 2004 Vol.47 Supp. 1 142- -151Study on the changes of water cycle and itsimpacts in the source region of the YellowRiverZHANG Shifeng', JIA Shaofeng', LIU Changming , CAO Wenbing",HAO Fanghua, LIU Jiuyu4 & YAN Huayun51. Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences,Bejing 100101, China;2. China University of Geosciences, Beijing 100083, China;3. Beijing Normal University, Beijing 100875, China;4. Bureau of Hydrology of Yellow River Conservancy Commission, Zhengzhou 450003, China;5. Bureau of Hydrology and Water Resource Investigation of Qinghai Province, Xining 810001, ChinaCorrespondence should be addressed to Zhang Shifeng (email: zhangsf @ igsnrr.cn)Received January 18, 2004; revised April 8, 2004AbstractThe water cycle in the source region of the Yellow River underwent greatchanges in the 1990s. The major features of the changes are as follows: the gaugedrunoff declined significantly while the precipitation increased slightly, and the runoffprocess was more concentrated on the flood season. Water balance analyses indicatethat the pondage was kept in thestatus of negative equlilibrium， causingeco-environmental problems. The runoff decrement is due to evaporation increment inthis region. Studies show that the runoff process in this region is closely related to that ofthe other hydrological stations in the upper reaches. When the runoff declines in thesource regions, the amount of water also declines in the whole upper reaches of theYellow River, affecting the balance between water demand and supply. Meanwhilechanges will take place in the water cycle of the river course system when theeco-environment deteriorates. The trend of water cycle change in the source region isthat the runoff will keep declining with the increment of evaporation caused bytemperature rise in the northwest of China in the 21st century. But the hydraulicengineering in the source region will help to mitigate the deterioration of localeco-environment system, though the impacts to the lower reaches of this project may notbe the case.Key words: source region of the Yellow River, water cycle, evaporation, negative equilibrium.DOI: 10.1360/ 04ez0012The Yellow River originates from the QingrMH中国煤化工;Province. Con-cerming its hydrological, geological, geomorphicC N M H Geveral ways canbe found to define the source region of the Yellow River". The source region studied inCopyright by Science in China Press 2004Study on the changes of water cycle and its impacts in the source region of the Yellow River143this paper is in the most narrow sense. It lies in latitude 34°一-35°15' north and longi-tude 95*40'- -98°30' east!2- 4! The gauged area is 20930 km2, average precipitation 310mm, evaporation ability 1300- 1 600 mm, and the altitude is above 4200 m. This area istypical of arid plateau with an average temperature of - 4C and frost free period of 2-3 d.The runoff of the source region has declined sharply since the 1990s. Theeco-environment has changed significantly with biodiversity declining and grasslanddeteriorating. Up to now, a lot of researches of the impacts of climate changes oneco-environment in the source region have been donel5- 门. However, what kind ofchanges have taken place to the water cycle factors? What are the driving forces, andhow much is their contribution to the changes. This is yet a very important research as-pect to be studied.Water cycle factors and water balance assessment in the source region of theYellow RiverThe regional water balance principle is adopted as a basic way to analyze the char-acteristics of water cycle changes. The factors of water cycle in a given watershed in-clude precipitation, runoff, evaporation and pondage. The basic equation of water bal-ance is as follows:R=P- E土sW,(1)in which R represents the annualrunoff, P the annual precipita-tion, E the actual annual evapo-ration and△W thewaterpondageindicatingLanzhouamount variations in soil, lake,Guide XunhuaS~reservoir and river system. Then m Huangheyan(Tangnaihaichanges of water cycle can bereflected by the changes of theseMadu6Jungongfactors.l Jimai、Maq电Fig.1 is the sketch of thesource region of the YellowTangkeRiver. Huangheyan station is thehydrological control station of0.75_150300，kmthe source region above Maduo.Fig. 1. The sketch of the source region of the Yellow River.Gauged data of precipitation andrunoff at Huangheyan station is employed in theanwhile the run-off has been restituted into natural runoff in the co中国煤化工activities.YHCNMHGConsidering human activities in the source region, the measured runoff will be con-www.scichina.com144Science in China Ser. E Engineering & Materials Science 2004 Vol.47 Supp. 1 142- -151verted into natural runoff by the way of restitution. The formula of the restitution ofnatural runoff in a watershed is as follows:RN= RM+ RA + Ri+ Rp+ Rr.(2)In the above formula, RN and RM represent natural runoff and measured runoff. RA,Rq and Rp represent water withdrawal by agricultural, industrial and domestic use re-spectively, and Rr represents water pondage amount in the reservoir and lakes in a givenperiod. There is very limited water use by industry and agriculture, while domestic useand livestock drinking constitute a major part. The most significant restitution amount iscaused by livestock drinking with the sharp increase of livestock population. Domesticuse is also an element of water restitution. By the end of the 1990s there was a popula-tion of 10000 people in the source regionb, ' ' and they were mainly living on animal hus-bandry. The livestock has been tripled in the past 30 years since the 1970s', and nowthe total population of the livestock is 3.5 million. Suppose the quota of livestockdrinking is 40 L/d per head, and that of domestic use is 60 L/d, doubled as before, theresults show that there is an increment of 0.0011X 10* m3 for domestic use and 0.3833X10% m' for livestock drinking. From the 1950s to the 1990s the total increment of domes-tic use and livestock drinking is 0.3844X 108 m'. Pondage Rr in formula (2) is includedin OW in formula (1) according to their definitions, therefore Rr can be covered in waterbalance calculation in formula (1).Considering the evaporation theory and the similarity principlel8.i9, the authoradopts the evaporation data from the water balance stations of empty glacier poket inTianshan and ice lead in Qilianshan'[20.,211which have similar climate conditions to thesource region of the Yellow River. The actual evaporation data of the source region canbe projected by different coefficients. The adjust coefficient is 0.21 for 1950- 1969,0.21 for 1970- 1989 and 0.245 for 1990- 1999. Then formula (1) is used to calculatepondage sW. The result is given in table 1.Table 1 Water balance result in the source regionPrecipitationRunoff/108 m3Natural runoffEvaporationPondage/mmmeasurednatural1956-- 1989302.47.37.4335.5287.7-20.81990- -1999327.64.985.4926.2329.2-27.8Mean309.86.636.8832.9299.9-232 Characteristics and reasons of water cycle changes in the source regionTable 1 shows that the precipitation and evaporation, the two most important ele-ments to decide the basic features of water cycle, are around 300 mm. The actual gener-ated runoff is around 26- -35 mm, which is ve中国煤化工the amount ofevaporation and precipitation. The runoff coefficid|YH.CNMHGpondageis-21--38 mm, which is also relatively small compared to precipitation and evaporation, butCopyright by Science in China Press 2004.Study on the changes of water cycle and its impacts in the source region of the Yellow River145it is close to the amount of runoff, therefore it may play a very important role in runoffgeneration.2.1Slight precipitation increment and remarkable runoff decrementAnalyses on the data of precipitation and runoff in the Yellow River source regioncollected in the past fifty yearsl22 26]indicate that the mean precipitation is 309.8 mm.The precipitation has changed from 302.4 mm in the period of 1956- 1989 into 327.6mm in 1990- 1999. There was an increment of 8% or 25.2 mm. Therefore it can beconcluded that there was a slight increment in precipitation in the 1990s. The mean run-off is 6.88X 105 m'. The runoff has changed greatly from 7.43X 108 m3 in the period of1956- 1989 to 5.59X108 m3 in the 1990s. There was a decrement of 26.1% or 1.94X10*m3 in runoff. The river flow drained out frequently in the 1990s. Therefore the majorcharacteristic is that the runoff declined significantly while the precipitation did not de-cline.Meanwhile, the distribution of the runoff has also changed within a year. Table 2shows the percentages of runoff in different periods of a year. The period of 1950- 1960was a mean to drought series, during which 56.6% of the total runoff was discharged inthe flood period, i.e. from July to October. The period of 1970- 1980 was a mean torainy year series, during which 55% of the runoff was discharged in the flood period.But in the 1990s, the ratio of the runoff in the flood period rose up to 61.7% while thetotal runoff declined; the ratio of other 8 months decreased from about 45% to 38.3%.The runoff ratio from July to September increased significantly although its absoluteamount decreased, while the amount as well as the ratio of the runoff decreased fromOctober to March. The relative concentration of runoff in flood period causes unevendistribution in a year, which would result in flow drain off during the non-flood periodsin an extreme situation.Table 2 The ratio of monthly discharge at Huangheyan Station(%)"Mar.Apr. MayJun.Jul.Aug.Sep.Oct. Nov. Dec. Jul-Oct.1956- 1979 4.7 4.2.35.0.15.110.5 14.3 15.915.9 9.06.0 56.61980- 19895.4.54.4.86.5.11.9 14.014.914.38.96.255.11956- 1989 5.2 4.34.24.74.96.011.3 14.1 15.314.9 8.96.1 55.61990- 19994.33.45.46.413.5.18.812.961.7Total series4.111.6.，14.8 15.514.68.65.9 56.5a) Source: Data in this table is provided by the Yellow River Conservancy Commission.2.2 Increasing temperature and evaporationThe evaporation change is another characteristic of water cycle in the source region.Analyses indicate that the evaporation in the source region was 287.7 mm in the periodof 1950s- 1980s, which was slightly less than the中国煤化工ime period. Theevaporation was 329.2 mm in the 1990s, slightlyi CN MH Gation. It can beconcluded that the runoff generation is dependant on ponaage uinciuaing lake and soilwww.scichina.com146Science in China Ser. E Engineering & Materials Science 2004 Vol.47 Supp. 1142- -151moisture) releasing. The evaporation has changed considerably and there was an incre-ment of 14% in evaporation from the 1950s to 1990s, or 41.5 mm. .YearThe climate in the source region.1950 1960 197019801990 2000 2010experienced a cold period in the 1960s一-3-1970s and the warming in the 1980s-1990s, but the general tendency is thatthe temperature has been going up in the5tpast fifty years. Fig. 2 shows the changeof temperature in Maduo Station and it-6LFig.2. Changing tendency of temperature in the sourcecan be clearly found that the temperaturewas increasing in the past years, which isregion.also the reason of evaporation increase.The average temperature increased from the 1950s to 1990s, and the relations be-tween temperature and evaporation are shown in fig. 3. .The relationship between evaporation andtemperature can be described as follows:350300E = 22.767t + 388.56,，r2 = 0.303 (3)250200This formula indicates that there is a lin-昌150ear relation between temperature and evapora-100-6--3tion.Temperature/ CFig. 3. Relationship between temperature andEvaporation will increase when tempera- evaporation in the soure region.ture goes up. Quantitative analyses indicatethat when there is an increment of 0.1°C in temperature, the evaporation will increaseby 2.28 mm, which equals to 4.77X 10* m'. The increase of evaporation will certainlycause the decrease of runoff.2.3 The pondage in long term negative equilibriumSoil moisture and water in the lakes are changing because of climate conditions andhuman activities. Water equilibrium could be either positive or negative in a year, and itis positive with humid climate and rich precipitation in a year, while the pondage isnegative with dry climate and less precipitation in a year. The pondage is normally closeto zero in a long term. But the calculation shows that there were relatively more negativeequilibriums than positive ones in the past fifty years. The cumulative pondage amountwas - -1012 mm from 1956 to 1999. To be specific, the pondage was - 20.8 mm from1956 to 1989 and - -27.9 mm from 1990 to 1999. This also demonstrates that the waterresource conditions have been worsening in the nast fiftv_ vears hecase of water with-drawal by human activities as well as evaporaticMH中国煤化工as kept releasingwater in the past fifty years and it is the same to t]C N M H Gegion, and waterrelease sped up in the 1990s. This also causes the fall of the water level of the Eling lakeCopyright by Science in China Press 2004Study on the changes of water cycle and its impacts in the source region of the Yellow River147and the Zhaling Lake, which are the two major lakes with total area of 1100 km^ in thesource region. The recession of the Eling Lake, the Zhaling Lake and groundwater is theoutcome of long- term negative equilibrium, which is another outstanding characteristic,the cumulative pondage is negative (see fig. 4). It is the above characteristic that causesthe continuous worsening of the water resource conditions in the source region, and alsoresults in the disappearance of many lakes.15010050-50-100-150200Fig. 4. Water balance in the source region of the Yellow River.To sum up, other factors of water cycle have changed greatly except precipitation.The major characteristics are evaporation increase, runoff decrease and negative equilib-rium of the pondage .2.4 The causes of water cycle change in the source regionIn the condition where the precipitation was not reduced, there was a 31.8% dec-rement of the measured runoff and 26. 1 % decrement of the natural runoff. From thepoint of water cycle mechanism, the above phenomenon is caused by the vulnerability ofthe hydrological system. Both the precipitation and evaporation are much larger thanrunoff. The runoff would change greatly when there is a slight change in either precipi-tation or evaporation. With the analysis of natural environmental change and human ac-tivities, the runoff decrease can be attributed mainly to evaporation rise and also partlyto domestic water withdrawal.According to the above runoff restitution calculation, the water consumption was0.1289X108 m3 and 0.5132X108 m' in the 1950s- 1980s and the 1990s respectively.The water used by domestic life and livestock drinking accounts for 1.7% and 9.3% ofthe natural runoff. Human activities play a more important role than ever before. How-ever, domestic water use is limited in water balance, and the effect of climate change isdominant. The evaporation in the source region increased by 41.5 mm from the 1950s tothe 1990s, equal to 8.69X 108 m', which is larger than the average runoff amount in thesource region. Precipitation increased by 25.2 mm,中国煤化工The differencebetween the increments of evaporation and precip:MYHCN MH G，causing thewww.scichina.com148Science in China Ser. E Engineering & Materials Science 2004 Vol.47 Supp. 1 142- - 151recession of groundwater, lakes and soil moisture. Therefore the evaporation rise is thedecisive factor to affect water cycle process in the source region of the Yellow River.Eco-environment change may also take back action on water cycle process. Therunoff in the non-flood season is generated by base flow, for the precipitation is small inthe source region during this period. The water release from groundwater and soil mois-ture would decline if the groundwater level keeps fallingwithworseningeco-environment. This may cause the decrease of the runoff and eventually drying up ofthe flow. Water cycle features will then change severely.3 Impacts of water cycle changes in the source region3.1 Runoff reduction will intensify the conflicts of water demand and supplyThe Yellow River basin is an area with scarce water resources. The water modulusof surface runoff is 7.7X 104 mi /km", much lower than the average modulus in China,which is 28.8X 10+ m/km2. The runoff modulus for the source region is merely 3.36X10* m'/km2, much lower than that of the Yellow River. The water demand and supplyconflicts have existed for a long time, and runoff reduction in the 1990s intensified theconflicts.Although the runoff amount in the source region only takes up a small portion,there are close relations in runoff processes among the hydrological stations in the upperreaches, i.e. there are similar reduction tendencies in Huangheyan, Jimai, Maqu andTangnaihai hydrological stations (see table 3). The area controlled by Tangnaihai Stationis 12.2X10* km2, 16.2% of the Whole Yellow River basin. The runoff is 212X 10* m,35% of the whole Yellow River basin. The water amount generated above TangnaihaiStation plays a key role in the whole Yellow River basin.Table 3 Runoff relations of the stations in the upper reaches of the Yellow RiverHydrological stationsCorrelationHuangheyan-JimaiY= 1.9871x+ 25.071，r = 0.7619Jimai-MaquY= 2.2563x + 54,户= 0.8701Maqu-TangnaihaiY= 1.4332x- -3.7805，2 = 0.9601Huangheyan-TangnaihaiY= 6.7292x+ 156.28， = 0.6226Although there are very close relations in runoff processes, the runoff reductionpercentage is different due to the huge difference in their controlled areas. The runoffreduction is 25.8% in Huangheyan Station, and 8.5% in Tangnaihai Station in the 1990s,but they have similar tendencies. The upper reaches, called“Tower of the Yellow River",is a major water resource region, and the water generated in the upper reaches will beused in the northwest and north China. Therefore the runoff reduction in the source re-gion will affect the water supply system as a whol中国煤化工YHCNMHGCopyright by Science in China Press 2004Study on the changes of water cycle and its impacts in the source region of the Yellow River1493.2 Groundwater recession and eco-environment deteriorationWater cycle changes result in the reduction of water, which in turn causeseco-environment deterioration. There are three aspects demonstrating the deterioration ineco-environment in the source region.The first aspect is the recession of groundwater and water surface. There used to be4000 lakes in the upper reaches vicinal to the source region in the 1950s. Now the num-ber of lakes has been reduced to 2000. Water storages of the Eling Lake and the ZhalingLake are about 100X 10 m3 and 40X 108 m3 respectively; the areas of the two lakes are608 and 542 km"; the depth of the two lakes were 20 and 8 m. Now the water level hasfallen by 2 m and the water surface area is also decreasing. Therefore the phenomenonof lake recession and water level recession can be regarded as the reaction to runoff re-duction. On the one hand, the runoff reduction will cause the lake recession and waterlevel recession; on the other hand, water reduction of the Eling lake will cause the riverflow drained up.The second aspect of eco- environment deterioration is pasture destruction, causingdesertification and rat prevalence. Due to water level recession, human activities andover grazing, the vegetation in the source region has been distroyed seriously. Since theanimal husbandry is the major economic activities, unreasonable grazing has caused thegrassland degradation. Take Maduo County for example, the land degradation area hasreached 10702 km2, which accounts for 42% of the total area. 7228 km2 (67.5%), 508km^ (4.7%) and 2966 km' (27.7%) out of 10702 km' are slightly, moderately and seri-ously degraded respectively. Grassland degradation always manifests as the decrease ofgrass production, increase of weeds and desertification. Because of the windy weather,overgrazing and soil frozen split, mountainous grass pad deteriorates to grit desert. Thereare already large deserts with a total area up to 260 km' in Heihe commune and Huanghecommune in Maduo County. Due to over hunting of animals, the living space for thesecondary consumers in the eco-system such as foxes, wolves and birds of prey isshrinking with reduced population of these animals, and primary consumers such as ratsand insects are prosperous, causing rat prevalence in the source region.The third aspect of eco -environment deterioration is river course shrinking. Thewater cycle has changed significantly in the source region because of temperature rise,evaporation increase, water development and hydraulic engineering construction. In thelong period of river drained up in the 1990s, there was no water flow in the river coursefor four to five months, and actually it has become a seasonal river. The above situationwill affect the river course development and the relation of river facies.4 The trend of water cycle change in the source regionThe water cycle underwent great changes in the 1990s with the joint action ofnatural process and human activities. All the facto中国煤化工ff, groundwaterlevel and soil moisture have changed greatly whilYHC N M H Gains unchanged.www.scichina.com150Science in China Ser. E Engineering & Materials Science 2004 Vol.47 Supp. 1142- -151Normally water cycle change is a progressive process under the action of natural factors.The above research indicates that the key factor to change is evaporation, the incrementof which has directly caused runoff reduction. The evaporation change is decided by thetemperature change. The temperature in the 21st century will go up according to someresearch, therefore the runoff in the source region will decline continuously.Human activities to affect water cycle may also be very strong. The impact of hu-man activities has been increasing in the past 50 years. The hydraulic engineering con-struction is a major way to affect the water cycle and eco-environment. The local gov-ernment started the construction of a reservoir with a capability of 15.2X 10* m' in 1998.The project is 17 km from the outlet of the Eling Lake, and the normal storage waterlevel is 4270.15 m. The reservoir started to store water by the end of 2001. Although theconstruction may provide power for the local people, the conservation of water in thefirst few years will affect the water discharge in the source region, and the measuredrunoff at Huangheyan Station will be changed greatly.There is also a very important positive impact on the source region with the con-struction of the reservoir. Along with the rising water level in the reservoir, the waterlevel recession in the Eling Lake and vicinity area will be suspended, which is favorablefor the restoration of the eco environment, or at least mitigates the worsening conditions.The lake disappearance will slow down and some lakes may be recovered.5 ConclusionsThe major characteristics of water cycle changes in the source region are that therunoff declined significantly in the 1990s while the precipitation was not reduced. Thedistribution process is more concentrated in the flood periods than ever before.The lakes, groundwater and soil moisture in the source region are in long termnegative equilibrium. The evaporation rise is the main reason for runoff decrease, andthe domestic water withdrawal also fairly played a role. The runoff reduction has causedeco- environment deterioration such as lake disappearance, groundwater recession andgrassland degradation.The runoff process of the Huangheyan Station in the source region has very closerelations with that of other hydrological stations in the upper reaches of the Yellow River.When the runoff at the Huangheyan Station declines, the water flow will also decrease atthe Tangnaihai Station, which will affect the balance of water demand and supply.Meanwhile runoff reduction will affect the river course development.The evaporation will go up in the 21st century as the climate keeps on warming inthe northwest of China. The runoff will decrease continuously, but the localeco-environment system in the source region wil; the constructionof the reservoir. Nonetheless, the impact of hydr:中国煤化工:truction may beCNMHGvery complicated for the lower reaches of the YellCopyright by Science in China Press 2004Study on the changes of water cycle and its impacts in the source region of the Yellow River151Acknowledgements This work was supported by the State Key Development Program for Basic Sciences ofChina (Grant No. G19990436) and the Knowledge Innovation Project of the Chinese Academy of Sciences (GrantNo. KZCX1- 10-03).References1. Ding Yongjian, Yang Jianping, Liu Shiyin et al, Exploration of eco environment range in the source regionsof the Yangtze and Yellow Rivers, Acta Geographica Sinica (in Chinese), 2003, 58(4): 519- -526.Qi Mingrong, Proceedings on Source Region of the Yellow River Investigation (in Chinese), Xining: QinghaiPeople's Press, 1982Yellow River Conservancy Commission, The map of the Yellow River, 1986.Institute of Geography, CAS, Atlas of the Tibet Qinghai Plateau (in Chinese), Beijing: Science Press, 1990.5. 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