HISTORICAL DESERTIFICATION PROCESS IN HEXI CORRIDOR, CHINA

CHINESE GEOGRAPHICAL SCIENCEVolume 15, Number 3, pp. 245- -253, 2005Science Press, Beijing, ChinaHISTORICAL DESERTIFICATION PROCESSIN HEXI CORRIDOR, CHINAWANG Nai-ang, ZHANG Chun-hui, LI Gang, CHENG Hong-yi(College of Earth and Environment Sciences, Lanzhou University, Lanzhou 70000, P. R. China)ABSTRACT: Over the last 2000 years，approximately 38 ancient cities were abandoned through desertification inHexi Corridor, Northwest China. Among them, 21.05% were abandoned during the Northerm and Southerm Dynas-ties, 21.05% during the end of the Tang Dynasty and the Five Dynasties, and 57.9% during the Ming and Qing dy-nasties. At the same time, main lakes were shrinking rapidly from the 5th Century to the 6th Century and the end ofthe Qing Dynasty. The climate in these periods was relatively arid and cold with frequent dusts. The phase of thesechanges indicated that there were three periods of desertifcation enlargement in the northem China. They wereNorthem and Southem Dynasties, the end of Tang Dynasty and Five Dynasties, the Ming and Qing dynasties. Themacro-process of desertification in the study area was controlled mainly by the climatic changes. But from the factsthat the population density in the middle of Qing Dynasty had exceeded the critical index of population pressure inarid arca and the usage rate of water resources had exceeded 40% in Hexi Corridor, this paper also suggests that hu-man activities have played an important role in desertification processes of the study area mainly during the recent300 years.KEY WORDS: historical desertification; climate change; human activities; Hexi CorridorCLC number: P931.3Document code: AArticle ID: 1002-0063(2005 )03-0245-091 INTRODUCTIONsight of undulate dunes at present. It is the clear proofof desertification in nearly 2000 years. According to theHistorical desertification is not only the key issue on the geographic distribution and characteristics of desertifi-interaction between nature and human process, but alsocation, we can generalize these lands into 2 types: onethe most challenging issue in the complex relationshiptype is land where desertification took place near thebetween human and land. Previously, most Chinese sci-oasis of downstream river in desert regions, such asentists in this field carried out their research work main-Hexi Corridor and its surrounding regions, the other onely from the perspective of historical geography or is land where desertification took place in semi -arid andarcheology. One approach to analyze environmentalsemi-humid regions, with the most typical cases of Muchange is to study the rise and fall of the ancient cities Us Desert in Ordos Plateau and Horqin Desert in thein desert and to study the historical relics that recordedXiliao River valley.human activities. That is to say, they took the sites andThere are various complicated causes that lead to de-relics as the age signals of desertification. Another ap- sertification during historical periods，including bothproach is to study land collection and cultivation in his-the natural factors and the human dimensions. But dur-torical periods , mainly to take the stratigraphic relation-ng certain periods， the status and influence degree ofship between soil in culture layer and the soil in topsoil the two kinds of factors fluctuated in the desertificationlayer as the historical basis to confirm desertifcation.process. As for the study on the formation of the firstThe lower part of surface horizon is quicksand formedtype，much fruitful research has been done since theduring geologic time，while the upper part of surface 1990s. This paper takes the desertification around thehorizon is re-born sand formed during historical peri-Hexi Corridor and its surounding regions as the exam-ods. The ancient cities buried by sand and some famous ple to中国煤化工-nanistic backgroundgrasslands in the past in the northerm China take on the when th: happened (Fig. 1).Received date: 2005-04-08TYHCNMHGFoundation item: Under the auspices of the National Natural Science Foundation of China (No.40471138 ) and the National Key.Basic Research Project (No. G2000048701)Biography: WANG Nai-ang (1962-), male, a native of Yucheng of Shandong Province, professor, specialized in environmentalchanges and historical geography. E-mail: wangna@lzu.cdu.cn246WANG Nai-ang, ZHANG Chun-hui, LI Gang et al.9496°8°|100°|102°104*42Sogo Lake。Juyap Ancient Oasis一~AxitAdient Oasis inSanhu_JiyuguanBadain Jaran DesertAkesai SubeifoquanangyeShandannqinStudy areaJincbeng8°}YpngqhangL.TenggerDesertFig. 1 Distribution of the deserted ancient oases in Hexi Area2 METHODS6th century, countries such as Loulan, Qieme, Luobu-zhuang, Niya, Keladun, Guminfeng and Jingjue in theThis study included the scientific expedition to the an- Tarim Basin all collapsed one after another during thatcient cities and the "C dating besides the analysis of the time. It is not unique, but has its counterpart: the timehistorical document. Samples of wood block, grass rope when the lakes around the cities shrank and disappearedand other types were dated at the Laboratory of Science has relative consistency to these ancient cities' disap-Technological Archaeology & Cultural Relics' Protec- pearance. For example, Zhuye Lake's highest altitude ofion in Peking University and at the Laboratory of its water table was about 1310m in natural water systemChronology in Lanzhou University.epoch of prehistory (7000-6000a B.P.), but during theHan Dynasty and several hundred years after that，i3 RESULTS AND DISCUSSIONgradually separated into two unconnected parts: theWest Lake, which is now called Qingtu Lake, and the3.1 Climatic Background of Historical Desertifica- East Lake，which is now called Baiting Lake.' Thetion Processbiggest area of Juyan Lake once reached over 4300km2The occurrence time of desertification in different re-in prehistory stage. It lied at the end of the Heihe Rivergions can be compared, which is of significant impor- and was made up of old Juyan Lake, Suoguonuoer Laketance to discuss the desertification genesis. Accordingand Geshunnuoer Lake. In the Han Dynasty, the culti-to statistics，the abandoning times of ancient cities in vated area in Juyan region reached a stage of unprece-Hexi Corridor and its surrounding regions have gooddented growth. These lakes once were a good size be-consistency (Table 1). Among the deserted cities,cause of a plentiful supply, but they shrank greatly in21.05% were abandoned during the Northern and the 5th and 6th century A.D. During the Pre-Qin Dy-Southerm Dynasties, 21.05% from the mid-Tang Dy- nasty, Lop Lake had once a larger area. From its lacus-nasty to the Five Dynasties and 57.9% in the Qing Dy- trine sediments and shoreline length, it can be estimatednasty.that its maximum area could once reach ,5350km2 duringOn the other hand, when we compare the fluctuation its development. Till the 5th century, its girth was onlyof climate and the age when the ancient cities were a- 150k中国煤化工the Book of Han Dybandoned, we can easily find that climate was obviously nasty: the cold-arid phase ofcold and dry when the ancient cities fell to dust largely, the NC N MH Gies (about 200 to 589such as the Northerm and Southerm Dynasties，from the A.D.).Late Tang Dynasty to the Five Dynasties and the MingWhat were associated with desertification were dust'sand Qing dynasties. During the dry period ofthe 4th - release， transport and larger range influence in the at-Historical Desertification Process in Hexi Corridor, China247Table 1 Radiocarbon ages and abandoning times of main ancient cities in Hexi CorridorAncient cityMaterial dated 'C ageExisting stageAge of desrification1. Gaogoupu Fort of WuweiGrass rope195+50a B.P.Qing DynastyMiddle Qing Dynasty2. Qinfeng Town of MinqinHan, Tang and Ming dynastiea3. Baitingjun Town of MinqinWood block1305+58a B.P.Han and Tang dynatiesAfter middle Tang Dynasty4. Xishawo Town of Minqin1207+34a B.P.Han, Tang and West Xia dynastiesAfer middle Tang Dynasty5. Sanjiao Town of Minqin2520+80a B.P.Han and Tang dymastiesEnd of Tang Dynasty6. Duanzihao Town of Minqin Carbon debris 1270+48a B.P. Han and Tang dymastiesMing and Qing dynasties7. Dong'an Fort of MinqinWood bar120180a B.P.West Xia, Yuan and Ming dynasties End of Qing Dynasty8. Hongsha Fort of MinqinTang, Song, and Ming dynastiesMiddle and late Qing Dynasty9. Qingsong Fort of Minqin10. Shashan Fort of MinqinMing aind Qing dynastiesMiddle and late Qing Dymasty11. Nanle Fort of Minqin12. Hongya Fort of MinqinLate Qing Dynasty13. Shacheng Town of Yong-Han, Jin and Tang dynastiesMiddle Tang Dynasty and Five Dynastieschang14. Dichi County Town ofHan and Jin dynastiesNorthem and Southem DynastiesMinle15. North Heishuiguo Town ofWood block & 780+50a B.P.Han and Tang dynastiesZhangyegrass rope16. South Heishuiguo Town ofWood block & 190+50a B.P.Tang, West Xia and Yuan dynasties Middle and late Qing Dynasty17. Luotuo Town of GaotaiWood block 1428+56a B.P. Tang Dynasty18. Jiankangjun City of GaotaiNorthem and Southern Dynasties,19. Xusanwan Town of GaotaiHan, Tang and Ming dynasties20. Minghaizi Town of Sunan484+50a B.P.Ming Dynasty21. Xindunzi Town of SunanBone1840+80a B.P. Han, Tang and Ming dynasties22. Caogoujing Town of Sunan Wood bar613+58a B.P.23. Huishui County Town of Wood block1580+70a B.P.Han and Jin dynastisNorthemn and Southem DymasticsJinta24. K710 Town of EjinHan Dynastyorthem and Southern Dynasties25. A8 Town of EjinNortherm and Southem Dynasties26. K688 Town of Ejin27. F84 Town of EjinNorthern and Southerm Dynasties28. K749 Town of EjinNorthem and Southerm Dynasties29. K789 Town of Ejin2380+62a B.P.Ming and Qing dynastis30. Lucheng Town ofEjin2607+62a B.P.Han, Tang and Yuan dynasties31. Heicheng Town of Bjin1008+40a B.P.West Xia and Yuan dynasties32. Pochengzi Town of Yumen Wood block1390+50a B.P.33. Jinchangjun City of Anxi1017+60a B.P. Han and Tang dyastiesEnd ofTang Dynasty and Five Dynasties34. Bulongicao Town in AnxiReed1585+76a B.P.35. Ming'an County Town ofHan, Tang and Qing dynastiesAnxi36. Suoyang Town of Anxi1230+58a B.P. Tang, Yuan and Ming dynasties37. Toubao Town of Anxi364+64a B.P.End of Qing Dynasty38. Shouchang County TownHan and Tang dynastisof DunhuangNote: The C ages were measured in the Laboratory of Science Technological Archacology & Cultural Relics' Protection, PckingUniversity and in the Laboratory of Chronology, Lanzhou University.mosphere. With the rapid development of desertifica- above facts, we can suggest that dust record is one im-tion, the occurrence frequency and intensity of paroxys-portant index of desertification during historical peri-mal wind-sand disaster or dust storm were growing. Ac- ods. ZHANG De-er (1984) has even drawn a frequencycording to the statistics of dust storm occurrence, therecurve中国煤化工A.D., in which therewere 5 times in the 1950s，8 in the 1960s， 13 in the are 5over the last 10001970s, 14 in the 1980s, and 23 in the 1990s. The fre- years. 1 utey werc ull 1UwYHICNMHGo1o120quent occurrence of dust storm corresponded to the ex- 1470 to 1560, 1610 to 1700 and 1820 to 1890 A.D. re-pansion of desert at the same period in China. From the spectively. We can relate these stages with the corre-248WANG Nai-ang, ZHANG Chun-hui, LI Gang et al.sponding stages of the temperature curve in the latest years from the middle of the Tang Dynasty to the Five5000 years that ZHU Ke .zhen (1973) simulated. Then Dynasties (middle period of the 8th century to end ofwe can find out that, on the whole, dust storm's frequent the 9th century) ( ZHANG, 1996). And it was veryoccurrence periods were consistent with low tempera- likely that it was this cold stage that led to frequent warsture periods. At the same time, when we compare them in Hexi regions. One famous Chinese poet YUAN Zhenwith the humidity index curve in the eastermn China dur- (from 779 to 831 A.D.) wrote a poem named Dancing ining the latest 2000 years, we can find out that the peri- Xiliang， in which there was a few sentences as follow-ods were also consistent with dry climate stages. The ing:“I have heard that there were so many people indifference in dust frequency under cold or warm climate Xiliang State and there was abundant output of agricul-backgrounds was caused by the dynamical condition ture before.". "But after the Tang Dynasty's control inthat attributes to the change of the atmospheric-circula- China, the Huanghe (Yellow) River and the Huangshuition under both cold or warm climate periods. During River turned to dry up and there were only sand dunethe cold stage, the center of Siberian high and Aleutian left." These verses record environmental change of thatlow shifted southward, winds in winter became stronger period, especially the last sentence showed that desertand the polar front region shifted southward to 25°- -30° started to expand and many ancient cities or tribes be-N. On the other hand, the lacustrine deposits and the a- gan to fall at this stage. One famous scholar MA Du-bandoned farmlands in ancient oasis were exposed to an-lin, who lived between the late Song Dynasty andsurface because of the drought or shrinkage of lakes. early Yuan Dynasty (from 1254 to 1323 A.D.), record-These regions would usually become the origins of sand ed the following in his works All Study of. Literature:storm or desertification under strong wind erosion. The "After the middle period of the Tang Dynasty, the landstime consistency between the falling of the ancient in Hexi regions suddenly turned to desert, which wascities, lake shrinkage or drying up and dust storm's fre- controlled by outer tribes and did not have the same de-quent occurrence is more than a coincidence, which in- gree of fertility." All lands in the northwest of Chinadicates that the dry and cold periods of the last 2000 were not the same degree of fertility as before since theyears were the physical background that controls the confusion of AN and SHI in the Tang Dynasty. Even ifmacro-progress of the occurrence of desertification.the famous general YUAN Hao had great valor in warFirst of all, the long-term transition to dry and cold cli- and controlled lands as broad as Liang State, who wasmate would gradually make the environment of the an- just one of the outer tribes living in the barren lands.cient cities for human inhabitation worse, leading to de- What is worthy of attention is what was depicted in thiscrease in water supply and abandonment of the cities in treatise. For example，it was pointed out that Hexi re-the end. Secondly, climate could affect the fall of the gions changed into deserts or barren lands after the mid-ancient cities not only directly through affecting water dle of the Tang Dynasty. The economic boom of Hexisupply, but also indirectly through other social factors. Corridor lasted over 100 years since the Sui and theFor example, war once had an important effect on the Tang dynasties, and the scale of its exploitation wasdestruction and fall of some ancient cities. In dry pe- nothing less than that during the Ming Dynasty. Butriods, the successive drought did great harm to agricul- why did the desertification begin rapidly during thetural production, especially grazing sector. The yield Tang Dynasty? The key answer to the question is con-could not meet the basic needs of the rising population nected with the climate of China, which was warm andin warm and humid stages, consequently, speeding up humid in the Sui and the Tang dynasties but cold andthe aggression from nomad people. For example, the Ti- dry in the late Tang Dynasty.betans broke in after the AN and SHI's Rebellion on the14th year of Tianbao in the Tang Dynasty (755 A.D.). 3.2 Human Activities as Main Factors of Desertifica-Hexi Corridor and its surrounding regions were cap-tion since Middle of Qing Dynastytured one after another, which led to sharp decrease in The study of desertification of ancient oasis and ancientthe population and abandonment of vast fertile farm- lakes in Hexi Corridor involves many unresolved im-lands. During the 200 years between the 2nd year of portant academic questions about the environmentalGuangde in the Tang Dynasty (764 A.D.) and the pe- evolut中国煤化工na, such as whetherriods of Chunhua in North Song Dynasty (990 to 994A. the clCHCN MH Gwhether discharge ofD.)， Hexi regions were basically out of the control of rivers ueercaseu or nol, Line ucyree of influence of hu-Central Plains government administration. Formerre- man activities on the shrinkage or dry-up of inlandsearch showed that there was a cold stage of about 150 lakes and the desertification of ancient oasis. The rea-Historical Desertification Process in Hexi Corridor, China249son for the dry-up of so many lakes and desertification population in the drainage area of the Shiyang River inof ancient oasis might be the change of climate and riverWuwei Shire would exceed 100 000. With the estima-channels, or unreasonable human activities, or both of tion of 0.79ha of cropland per capita in the Han Dy-the physical and human progress. The key to determine nasty, the total area of cropland in the drainage area ofthe result lies in separating human factors from the e- the Shiyang River would be 80 000ha or so. Supposedco-destruction information obtained from lacustrine de- that the annual runoff amount and gross irrigating rationposits and ancient cities' site，such as the relationship in the Western Han Dynasty were the same as today, i.e.between population and resources carrying capacity, re- 1687x 10m3 and 6930m/ha respectively, the using ratelationship between sharp degradation of environment of the water resources at that time was 33% in theand the appearance of refugees，fights or wars for re- whole drainage area, so the :water resources was abun-sources control. According to these principles or char- dant for human use. In fact, we can also get the result toacteristics，we knew that overpopulation in the 18th know the prosperity of Hexi Corridor regions throughcentury in this region has deep and significant meaning.the record in Records of Geography in the Book of HanWe have just discussed the climatic background ofde- Dynasty History: "Once there was a party, everyone ofsertification of ancient oasis during historical period,that the country can attend to have a good time whetherand in fact, human activities made a rather important his status is gentle or simple. Even when there was aimpact on the desertification too. Among all kinds of bad harvest after natural disasters, the price of cerealhuman factors, population is not only the most impor- was low as usual and the thieves or robbers seldomtant index that eflects human activities, but also the ba- turned out. The reason is that the air of the whole coun-sic factor that leads to occurence and expansion of the try was so united and harmonious that it had superioritydesert. With the rapid increase in population and the to the inland countries". Because of the social stability,wide use of bronze wares and iron wares, the impact of economic progress and traffic fluency，Wuwei Shire,human activities on environment was gradually Zhangye Shire, Jiuquan Shire and Dunhuang Shire, notstrengthened. However, it has both positive and nega-only were the important martial beachheads and localtive function clearly leading to opposite results. On the administrative centers of northwest borders in the Hanone hand, to make a living，human being carried outa Dynasty, but also played an important role in interna-series of activities such as farming，logging and even tional trade between China and other countries. Biogra-fighting. Vegetations and soils on the land surface were phy of Kong Fen in the Book of Post-Han Dynasty His-so greatly transformed that the process of desertification tory recorded: "Guzang (former name of Wuwei) was abegan in the form of wind erosion, wind transportation wealthy city because of the trade with other minoritiesand wind-drift sand accumulation and so on (DONG et lived there at that time,”and there were four times foral., 1998). On the other hand, we cannot deny the fact trade every day. The residents in the city could have be-that the reverse process of desertification has ever partly come rich in several months." According to the markettaken place under the influence of human activities, es- trade in the ancient time，there were generally threepecially in the process of the transformation from aridtimes for trade everyday in the past. For example, in Lu-desert to oasis. For instance, with the deep influence of oyang,capital of the Eastern Han Dynasty andhuman activities, the area of Nanhu Oasis in Dunhuang Chang'an, capital of the Western Han Dynasty，thereincreased by about 10km2 compared to the ancient.were three times for business every day，a normal mar-The population of Hexi Corridor rarely exceeded ket, a momning market and an evening market in the Han400 000 from the Han to the Tang dynasties, and water Dynasty. All facts mentioned above reflected the busi-resources were mainly used to meet the need of irriga- ness prosperity at that time. Biography of Xiyu in thetion and everyday life, so land exploitation did not play Book of "Post-Han Dynasty History described: "Pedlarsa leading role in the change of water ecological or phys- were weighed down with business among post housesical environment. According to the record of Records of every month and gathered frontier fortress every day".ItGeography in the Book of Han Dynasty History，there related to national politics and economy in that regions,was a population of 76 000 in Wuwei Shire, 88 000 in but it must be emphasized that it was the second warmZhangye Shire, 77 000 in Jiuquan Shire and 38 000 in climatic中国煤化工ears (ZHU, 1973).Dunhuang Shire respectively till the end of the Westem In contr:1 the whole HexiHan Dynasty. So if we included the number of sol- CorridorMYHCN MH Gding toA Surerydiers engaging in farming, the population could reach of Landform in the Book of Wei Dynasty History,400 000 or so in Hexi Corridor at that time. Then the while the area of desert expanded because of a rela-250WANG Nairang, ZHANG Chun-hui, LI Gang et al.tively dry and cold climate before the mid-6th century. Ming Dynasty according to the 13th volume of ActualOne clear proof was that Zhuye Lake was separated into History of Royal Genealogy in the Earlier Ming Dynasty.two discontinuous parts: the West Lake，and the East The population was about 338 000 according to theLake. The area of land under cultivation (including the population growth rate calculated through the increasearea cultivated by soldiers, farmers, temple or nun and rate of the cultivated area east to Jiayuguan State inso on) was 213x10>ha，which was equivalent to one Hexi region after the mid-Ming Dynasty. The Turpansthird of that nowadays. There were 22 462 households occupied the drainage area of the Shule River westin five counties of Liang State in the first year of Tian- to Jiayuguan State, where the population was aboutbao in the Tang Dynasty (742 A.D.). The population 10 000. The total population was about 350 000 in Hexiwas about 120 000. According to the standard of4.3ha region after mid-age of the Ming Dynasty, among them,per household, the total area of cropland was about the drainage of the Shiyang River accounted for 48%,97.3 x10ha，corresponding to 78.6x10ha in present the Hei River valley 49%, the Shule River valley 3%. Avalue in the drainage area of the Shiyang River valley. great deal of immigrants came to Hexi region becauseThe total was about 89.3 x 10*ha if cropland cultivated of political stability in the Qing Dynasty. According toby soldiers was included. In fact, the using rate of water A New General Survey During the Year of Jaqing inresources was about 37% at that time, which indicated Qing Dynasty，there were 255 000 households in Ganthat the exploitation and utilization degree was still un- State, Liang State, Su State and Anxi State of Hexi Cor-der the threshold value of 40% used widely in the world ridor. The total population would be 1 274 000 on thethough human activities had more effect on physical assumption of 5 persons per household. For the firstbackground than the Ming Dynasty.time, the population density in Hexi Corridor rose to 8.8Supposed that climatic change affected mostly the per square kilometer and broke through the critical in-slow expansion of the desertifcation in the northern dex of population pressure in arid region (it was set at 7China before Little Ice Age, the effect of human activi- persons per square kilometer in the intermational meet-ties became the primary cause in the process of deserti- ing of United Nations Conference on Desertificationfication during the recent 300 years. The cultivated area 1977). Human activities gradually replaced physicalwas 16 300ha in ancient district of Hexi and Xining re- factors and became the chief impact on environmentalgion in the early Ming Dynasty. It became 45 995ha changes in Hexi region. Actually, desertification ofduring the years of Wanli in the Ming Dynasty (1574- many lakes in Hexi Corridor began in past several hun-1620 A.D.)，which was 2.82 times that of the earlier dreds years (Table 2).Table 2 "C dating of sand dune of palco-lake in Hexi CorridorSampling siteSamplingAltitudePosition ofHeight ofMaterial dated'C agemumhernumber(m)physiognomydune (m)(a B.P)East to Huasan well in Huahai LakeHXSQ011223Terrace by the lake4.0Litter260+70HXSQ0212245.0425+60Lucao well in Huahai LakeHXSQ031225Barrier of the lake6.0Relict of Tamarix sp.240+40Natural bank ofHuahai LakeHXSQ041215Bottomland of the lakeRelict of Phragnites comnunis250+60Glauber's salt mine in Huahai LakeHXSQ051205158+50Beihaizi Lake in Jinta12202.780+58Chaiwan clled DuanziDZHCW011320Delta of the lake295+50Note: The "C ages were measured in the Laboratory of Science Technological Archacology & Cultural Relics' Protection, Peking Universi-ty and in the Laboratory of Chronology, Lanzhou University.In Shiyang River Basin, the population ranged ftom ty of water for agricultural irrigation to be 3.36x 102m330 000 to 50 000 in the upper and middle reaches ofthe or so，accounting for 19.9% of the gross water re-river before the Qing Dynasty. For example, the total sources in the drainage area of the Shiyang River, whichnumber of households was 7900 and the population show中国煤化工of farmlands in-was 46 300 in the whole region in the years of Yon- creaseation rate of water re-gle in the Ming Dynasty (1403- 1424 A.D.). There sourcYHCNMHGearsofWanliinthewere 48.5x10ha of farmlands totally, with 1 .05ha per Ming Dynasty (1573-1620 A.D.). During the year ofperson. Supposed the rate of gross irigation at that Qianlong in the Qing Dynasty (1736-1795 A.D.),time was the same as today, we can estimate the quanti- the number of popul ation jumped to 730 000 swiftly.Historical Desertifcation Process in Hexi Corridor, China251in the middle and lower reaches of the Shiyang River.Among them, 660 000 were in the middle reaches of邑1080-the river. If each person needed 200kg of food per year,50annual supplies to meet the population of 730 000was 1.46x10kg. Supposed that each hectare of farm-z9CLL _ 土.LLland could harvest crops 75kg，then 13 000ha farm-land must be brought under cultivation. Thus the water0虽员幸居昌虽昌勇星意邑虽for agricultural irrigation of that time could be 9x10*m3Yearor so, accounting for more than 53% of the gross waterFig. 3 Variation of the use rate of water resourcesin Shiyang River Basin in recent 2000 yearsresources in the Shiyang River basin. According to in-ternational standard, the quantity of water exploitationfrom a river could not exceed the limit of 40% of waterTang dynasties. There was still the record that "the tide offrom upper regions (generally, the gross using rate of Zhuyeze Lake in Zhenfan was so heavy that the well waswater resources is only 30% in arid region in the deluged" in the 39th year of Kangxi in Qing Dynastyworld). Thus it can be seen that the water resources of (1 700 A.D.). But by the 26th year ofQianlong in the Qingthe Shiyang River was changing from overplus to satu- Dynasty (1761 A.D.), the perimeter of Zhuyeze Lake wasration until exceeding the limit in the middle of the only 300 000m, and the area of the lake was probably lessQing Dynasty with the increase in population and farm- than 70km2(Table 3). The terminal lake in the tail reachlands (Fig. 2 and Fig. 3). The water discharge to Minqinof the Shiyang River began to shrink and became dry en-Basin decreased rapidly, which led to the outbreak of e- tirely after 1840, which led to the rapid expansion of de-cological crisis. Many lawsuits happened, for instance,sertification area. The areas of lakes in the east branch ofin order to resolve the conflicts in water use among the the Shule River and of Huahai Lake in the tail reach ofmiddle and lower reaches of a river between Minqin the Shiyou River ever got to 445km2 2000 years ago. ButCounty and Wuwei County in the early Qing Dynasty，then forth because the course changes in the Shule Riverand A Survey of Zhenfan State had special chapter about and artificial building of dam and dyke, the area of lakeslawsuits on water. We can look up the water usingshrank rapidly. At present, there are no dry lakes and bil-proportion between them stipulated by official litera- labongs formed during the progress of desertification ex-ure. The lakes shrank and became dried gradually be- cept for Ganhaizi Lake， which is a terminal lake in thecause of the increase in water use in the upper reaches, tail reach of the Beishi River with an altitude of 1204m.the decrease in water source supply and strong evapora-The area of Ganhaizi Lake that is the remnant of Huahaition. In the past, the landscape of lake was all kinds of Lake is about 300ha and its depth is about 0.1-1.5m. Theaquatic species and many dikes, especially fishes every- primary plants are Phraigmites communis in the lake andwhere, which have become past history.Tamarix spp. round the lake. There are millions of migra-tory or residential birds of 26 species in the lake, such as. 2.5Egretta garzetta, Grus grus and so on. So it was listed as三2.0natural reserve ofbirds in Gansu Province in April 1982.g 1.With the reclamation of farmlands in Sandun Shoal and1.0Bijia Shoal on the south bank of the Beishi River by im-唇0.5migrants in recent years, the water of the upper research-0邑员导号曼虽昌垦星虽虽虽es ofthe lake was dammed and used, leading the lake todry up drastically in June 1999. The natural reserve forbirds exists virtually only. It is a thousand pities thatFig. 2 Change of population in Shiyang RiverHuahai Lake, which had existed for 2000 years, vanishedBasin in recent 2000 yearsat the end of 20th century despite we emphasize ecologi-There were more than ten lakes in Hexi Corridor dur-cal protection today. According to the survey, it could being historical period and these lakes had mostly dried up attributed to excavating the ditch and using water to imi-now. The terminal lake in the tail reach of the Shiyang gate中国煤化工eriodic changes of cli-River once was named Dadjionghai Lake during the Sui mateMHCN MHG dryness.s The area ofand the Tang dynasties, and Baijianhu Lake in the Qing Juyan Lake, ncluuing Uujuyan Lake, Suoguoruo'er andDynasty; and the terminal lake in the of the JinchuanGashunnuo'er, once was more than 834km2 in historicalRiver was once named Changning Lake in the Sui and periods, which is the terminal lake in the tail reach of the252WANG Nai-ang, ZHANG Chun-hui, LI Gang et al.Table 3 Area changes of main lakes during the recent 2000 years in Hexi Coridor and its contiguous area (km)Name of lakeQin and twoEarly QingLate Qing Dynasty1950s1960s1970sHan dynastiesDynastyand the Republic ofChinaZhuyeze Lake2207(Huahai Lake4454910>>3Juyan Lake834953523550Lop Lake5350Shrink obviously6600Heihe River. R eclamation of farmlands was on a lar- land, building reservoir for water storage and so on.ge scale in Juyan region in the Han Dynasty, but theAccording to the paleobeach of terminal lake of thethree lakes such as East Juyan Lake， West JuyanShiyang River, the tendency of changes of lake levelLake and Juyan Lake existed with a fairly large area during the historical periods can be analyzed. If therebecause there was plenty of water at that time. Firstwas not the impact of human activities on environment,of all, Gujuyan Lake shrank and dried up because e- the lake would evolve in accordance with natural law,conomic activi ties mostly focused in Hexi Corridor. which means that the slope of lake area change in theMassive hydraulic structures were built in the middlerecent 7000a B.P. should keep constant. In fact, thereaches of the Heihe river, which lead to both reducing slopes of lake area change in the recent 7000a B.P. havesurface runoff of downstream and driving up riverbedchanged due to the impact of human activities on envi-on the east of river by mud and sand. Rivers flow. ronment. According to the varying range of slope ofinto the East and West Juyan Lake since the 1900slake area in the different historical stages, the influenceand the area of Juyan Lake still achieved 262km2 range of human activities on the shrink of terminal lakeuntil 1958. According to the statistics from 1949 tocould be estimated. The impact range of human activi-1984, the irigated area in Zhangye region in the middle ties on the terminal lake was about 30% during the lastreaches of the Heihe River enlarged by more than 6.67x 2000 years, and more than 80% in the recent 300 years10ha. The quantity of water for irigation increased to (Fig. 4).5.8x10*m3 if we assumed the ration of gross irrigationwith 38.67m2/ha. The quantity of evaporation was about 4 CONCLUSIONS3x109-4 x10'm2/a in Juyan Lake. Both the irrigatedarea of farmlands in the upper reaches of the HeiheIn short, the population density in Hexi Corridor did notRiver and of the grass fields in the delta of the Heihe exceed the critical index of desertifcation before theRiver enlarged, and the quantity of using water for irri-Qing Dynasty. To a great extent, the progress of deserti-gation increased too. The most important reason why fication was affected by climatic changes such as hu-the lake became dry-up eventually was that the quantitymidity and dryness. That is to say it is the result of a se-of water flowing into lake decreased continually during ries of climatic geomorphological consequence at dif-the late 50 years(approximately decreased by 7x10'm). ferent special and temporal scales. Thus the impact ofIt is ausual natural phenomenon that the lake shr- human activities on desertification is subject to naturalinks or becomes dried up, but it shrinks so fast that factors. This statement is consistent with what ZUthe area of lake decrease in a large scale. It only Rui-ping et al. (2001) found about environmentalhappened in arid region of the northwestern China. changes in oasis at the southerm part of Tarim BasinWe cannot gain a full understanding if we only con-during the recent 2000 years. The rapid growth in popu-sider climate change as the sole reason. The reason-. lation exceeds the critical index of the population pres-able explanation lies in that the growth of populationsure in arid land, which makes human activities havewas so quick that it exceeds critical limit of population more impacts on deserification than climatic changespressure. For the sake of it，people had to make use ofafter the mid-Qing Dynasty. Human activities becomewater resources and sacrifice ecological water on a the prir中国煤化工ion over the recentlarge scale. In particular， human activities directly 300 yeFluring the Ming andcause the rapid shrink of lakes，even' desertifcation Qing dyYHc N M H Globally and hitriduring the recent 300 years after the mid-Qing Dy- cal record showed an obvious increase in sand and windnasty，including destroying the forest reserve in the disasters, so we could not exclude the control ofupper and middle reaches of rivers, reclaiming waste cold-dry climatic background in the macro-progress ofHistorical Desertification Process in Hexi Corridor, China253700600自500Impact ofhuman activities and climatic change in rcent 300 yearsy-667.04x+19.96R-0.9536g 400300↓74 521x+82. 143200 tR2-0.84538143s and climatic change ia recent 2000 years100R'=0.730226”Time(aB.P.)Fig. 4 Impacts of human activities and climnate on the change of termninal lake in the Shiyang Riverdesertification.18(2): 156- 164. 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