Permafrost and climatic change in China

Ž .Global and Planetary Change 26 2000 387–404www.elsevier.comrlocatergloplacha

Permafrost and climatic change in China

Huijun Jin), Shuxun Li, Guodong Cheng, Wang Shaoling, Xin LiState Key Laboratory of Frozen Soil Engineering, Lanzhou Institute of Glaciology and Geocryology, Chinese Academy of Sciences,

260 West Donggang Road, Lanzhou 730000 People’s Republic of China

Accepted 26 April 2000

Abstract

The permafrost area in China is about 2.15=106 km2, and is generally characterized by altitudinal permafrost.Permafrost in China can be divided into latitudinal and altitudinal types, the latter can be further divided into plateau andalpine permafrost. Altitudinal permafrost also can be divided into five thermal stability types. The permafrost environmenthas changed significantly since the Late Pleistocene. In northeastern China, the southern limit of permafrost extended to41–428N during the last glaciation maximum; in the Holocene megathermal, it retreated northward. The ice wedges andpermafrost formed during the Late Pleistocene are still present in the northern part of the Da-Xing’anling Mountains. Theinactive ice wedges at Yitulihe indicate a cooling and subsequent permafrost expansion during the Late Pleistocene. Thelower limit of altitudinal permafrost in western China has elevated from 800 to 1500 m since the last glaciation maximum.Compared with that in northern Europe and North America, latitudinal permafrost in northeastern China is less sensitive to

Ž .climatic warming, but altitudinal permafrost, especially permafrost on the Qinghai–Tibet Plateau QTP , is sensitive toclimatic warming. Since the early 20th century, significant permafrost degradation has occurred and is occurring in mostpermafrost regions in China. Due to the combined influence of climatic warming and increasing anthropogenic activities,substantial retreat of permafrost is expected on the QTP and in northeastern China during the 21st century. Permafrostdegradation has and will cast great influence on engineering construction, water resources and environments in the coldregions of China. The wetlands in the cold regions of China emit significant amounts of CH and N O to the atmosphere4 2

and uptake atmospheric CO at a considerable rate, which might contribute to the global atmospheric carbon budget and2

feedback to climatic systems. However, uncertainties about permafrost changes, rates of changes and their environmentalimpacts are still large and call for intensive studying. q 2000 Elsevier Science B.V. All rights reserved.

Keywords: climatic change; permafrost; degradation; modeling; environment; China

1. Introduction

The permafrost area in China is estimated at about2.15=106 km2, accounting for 22.4% of the total

) Corresponding author. Department of Civil and Environmen-tal Engineering, University of Alaska, Fairbanks, AK 99775,

Ž . Ž .USA. Tel.: q1-907-456-6446 H , q1-907-474-5564 O .E-mail addresses: [email protected],

Ž [email protected] H. Jin .

Ž .Chinese land area Zhou and Guo, 1983 . Permafrostin China is mainly distributed on the Qinghai–Tibet

Ž 6 2 .Plateau QTP; 1.50=10 km , in northeasternŽ 6 2 .China 0.38=10 km and in the mountains in

Ž 6 2 .northwestern and central China 0.27=10 km .Permafrost in China can be divided into latitudinaland altitudinal permafrost. The area of altitudinalpermafrost approximates to 1.73=106 km2, ac-counting for 74.5% of that in the Northern Hemi-sphere. The altitudinal permafrost can be further

0921-8181r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved.Ž .PII: S0921-8181 00 00051-5

( )H. Jin et al.rGlobal and Planetary Change 26 2000 387–404388

Ž .divided into plateau and alpine permafrost Fig. 1 .The areas affected by frozen soils, including bothpermafrost and seasonally frozen ground, account for70% of the Chinese land territory. As a result, frozensoils have great influence on national economic de-velopment.

During the past 40 years, permafrost studies inChina have rapidly developed and have contributedconsiderably to engineering construction, enlightenedresource exploitation, and environmental protection

Ž .in the cold regions. Zhou and Guo 1983 summa-rized the principal characteristics of permafrost in

Ž .China. Cheng 1983 discussed the 3-dimensional

Ž .zonation of altitudinal permafrost. Zhou et al. 1991reviewed the Quaternary history of permafrost inChina. Some studies on permafrost in China havebeen summarized on maps, including the map of

Ž .snow, ice and frozen ground in China 1r4 000 000Ž .Shi et al., 1988 , permafrost distribution map in theDa- and Xiao-Xing’anling Mountains, northeastern

Ž . ŽChina 1r2 000 000 Permafrost Study Group in.Northeastern China, 1983 , permafrost map along theŽ . Ž . ŽQinghai–Tibet Highway QTH 1r600 000 Tong

.and Li, 1983 , permafrost map on the QTPŽ . Ž .1r3 000 000 Li and Cheng, 1996 , and numerousregional and specific maps. Some of these important

Ž . Ž . Ž .Fig. 1. Permafrost distribution in China I Latitudinal permafrost: a continuous permafrost; b discontinuous permafrost with islandŽ . Ž . Ž . Ž . Ž . Ž .taliks; c island permafrost. II Altitudinal permafrost: d alpine permafrost; e–f plateau permafrost; e continuous permafrost; f island

Ž . Ž . Ž . Ž . Ž .permafrost. III Non-permafrost: g seasonally frozen ground; h transitory frozen ground; i frost-free; j isogram of 0.5 m seasonallyŽ . Ž . Ž . Ž . Ž . Ž . Ž . Ž . Ž .freezing. Mountains: 1 Altai; 2 Tianshan; 3 Qilian; 4 Kunlun; 5 Tanggula; 6 The Himalayas; 7 Mahanshan; 8 Taibanshan; 9

Ž . Ž . Ž .Wutaishan; 10 Huanggangliang; 11 Changbaishan; 12 Da- and Xiao-Xing’anling.

( )H. Jin et al.rGlobal and Planetary Change 26 2000 387–404 389

maps have been digitized and included in the GIS-aided databases and models for cryospheric studiesin China.

2. Permafrost and climate at present

The development and distribution of permafrost inChina is mainly dependent upon climatic, geologic,topographic, hydrologic and surface cover condi-tions. Among the major climatic parameters, mean

Ž .annual air temperature MAAT and precipitationapparently control and influence permafrost. As aresult, permafrost distribution displays distinct verti-cal and horizontal zonation. The latter can be furtherdivided into latitudinal for global radiation distribu-tion and longitudinal zonation for regional variationsin aridity in China.

ŽAccording to linear correlation Qiu and Cheng,.1995 , in northeastern China, latitude is the most

significant factor in determining the MAAT, whereason the QTP, the vertical zonation of the MAAT ismost significant. In northeastern China and on theQTP, precipitation decreases northward, and in-creases eastward and upward, i.e. moisture comes

mainly from the oceans in the south and east. How-ever, in western China, such as in Xinjiang, precipi-tation increases upward, northward and westwarddue to moisture interception by high mountains.

The distribution of permafrost tallies roughly withthe variations of the MAAT and precipitation inthree dimensions. In northeastern China, the distribu-tion of permafrost reveals a latitudinal zonation.Permafrost decreases in its mean annual ground tem-

Ž .perature MAGT from 08C to y18C at its southernŽ .limit down to y2.48C locally down to y4.28C in

the north. Correspondingly, its thickness increasesfrom several meters to more than 100 m. The conti-nuity of permafrost varies northward from sporadic

Ž .to continuous permafrost zones Fig. 1 and Table 1 .In western China, which lies beyond the southernlimit of Eurasian continental permafrost zone, per-mafrost is present only in high mountains andplateaus, revealing an obvious vertical zonation, i.e.permafrost decreases in temperature and increases inthickness and continuity with rising elevations.

The latitude is the second important factor thatinfluences the distribution of the MAAT and, thus,the distribution and development of altitudinal per-mafrost. With southward increase of the temperature,

Table 1Basic characteristics of present-day permafrost in China

aType of permafrost Region Area Limit MAAT MAGT Continuity Thickness3 2 bŽ . Ž . Ž . Ž .10 km 8C 8C m

Horizontal continuous northeastern China 380–390 51–538N -y5 y2.5–y1.5 70–80 50–100discontinuous 47–498N -y3 y1.5–y0.5 50–60 20–50island y3 to 0 y1.0–0 0–30 0–20

Altitudinal alpine Altai 11 2,200–2,800 -y5.4 y5.0–0 -100–200Tianshan 63 2,700–3,100 -y2.0 y4.9–y0.1 16–200Qilian 95 3,500–3,900 -y2.0 y1.5–y0.1 5–140Hengduanshan 7 4,600–4,900 -y3.2Himalayas 85 5,100–5,300 -y2.5Huanggangliang 1,500–1,700Changbaishan 1,800–1,900 -y3.0Wutaishan 2,300Taibaishan 3,000

plateau Qinghai–Tibet 1,500 continuous 4,150 -2.5 y3.5–y0.2 30–80 25–175plateau island 4,640 y2.5–y0.8 y1.5–0 -30 -20–25

a In northeastern China, permafrost is divided into three types in areal continuity and its distribution is governed by southern limit in thelatitude of north. However, in northwestern China, permafrost distribution is generally controlled by elevation and exists only above lowerlimits, which are the lowest occurrence of permafrost on shadow slopes. Permafrost occurring sporadically in favorite localities is notincluded in this case. Permafrost on the QTP has different lower limits in each direction.

b Depth of soils with recorded subzero ground temperatures.


Table 2Ž .Thermal stability types of Permafrost and their areal percentage in China. Revised after Cheng 1983

Ž .Stability type MAGT Permafrost MAAT Areal continuity of permafrost %Ž . Ž . Ž .8C thickness m at lower limit 8C QTP Latitudinal Alpine

Extremely stable -y5.0 )170 y8.5 5 minor minorStable y5.0 to y3.0 110–170 y6.5 15 5 sizableQuasi-stable y3.0 to y1.5 60–110 y5.0 30–35 20–25 10–20Transitory y1.5 to y0.5 30–60 y4.0 30–35 30–40 40–50Unstable y0.5 to 0.0 0–30 y3.0–y2.0 10 30–35 30–40

the lower limit of permafrost ascends from 2200 min the Altai to 5100 m in the Himalayas.

The lower limit of altitudinal permafrost in Chinaalso has a general tendency to descend eastward. Forexample, in the Tianshan Mountains, it descendsabout 11 m for every 18 increase in longitude. Thelower limit of alpine permafrost is 2900–3250 m in

Ž X X .the sources of the Urumqi River 43806 N, 86850 EŽ .Qiu, 1993 . It is 1500–1700 m on Mt. Huanggan-

Ž X X .gliang 43820 to 448N, about 117830 E , and 1800–Ž .1900 m on Mt. Changbaishan about 428N, 1288E .

It eventually drops down to 1650 m on Mt. DaisetsuŽ .within 42–438N, 140–1488E , Hokkaido, JapanŽ .Sone, 1992 . In the Qilian Mountains between 36–408N and 93–1038E, the lower limit is 3600–3850 min the western section, 3680 m in the middle, and

Ž .3450 m in the eastern section Cheng, 1987 . Incomparison, the lower limit is 2300 m on Mt. Wu-

Ž X .taishan about 388N, 113830 E . In the KunlunŽ .Mountains 34–368N; 76–1028E , the lower limit of

permafrost is 4400–4500 m in the western part,4150–4200 m in the middle, and 3700–3800 m inthe eastern part; in comparison, it is at 3000 m in the

Ž .Taibaishan Mountains 348N, 1088E . Thus, the lowerlimits of permafrost and the MAAT descend east-ward in the middle to low latitudes, displaying atrend similar to that across the Eurasian continentŽ .Gavrilova, 1993 . In the mountainous regions ofsouthern Russia and the People’s Republic of Mon-golia, permafrost lower limits also descend eastward;for example, it descends from 1400 to 2000 m on thenorth slope of Altai Mountains down to 600–1200 m

Ž .in the eastern Sayan Mountains Yershov, 1989 .Ž .Cheng 1983 suggested that the lower limit of

permafrost in China would descend with increasingprecipitation in the regions south of 408N, whereas it

Ž .would ascend to the north of this latitude. Qiu 1993

argued that the influence of precipitation on per-mafrost is dependent on the seasons and forms ofprecipitation. Snowfall in winter and early springwould resist ground cooling, while snowfall in sum-mer would preserve frozen ground. To the north of408N, an increase in precipitation would generally beaccompanied by an obvious increase of snowfall incold seasons; to the south, an increased rainfall inwarm season; and in the mountains, an increase ofsnowfall in warm seasons. Thus, in the Altai andTianshan Mountains, precipitation reduction wouldenhance the eastward descending trend of the lowerlimits of permafrost caused by air temperatures drop-ping in the same direction. In northwestern Chinanorth of 408N, an eastward increase of precipitationwould mitigate the descending trend of the lowerlimits. On the QTP, and other mountains south of408N, the eastward descending of lower limits reflectthe combined effect of decreasing air temperatureand increasing precipitation.

Permafrost in China is warm due to the closenessof its temperatures to the freezing–thawing points ofsoils, which are vulnerable to climatic warming.Permafrost in China can be divided into five types

Ž .according to their MAGTs Table 2 . However, per-mafrost stability is determined and influenced bynumerous environmental variables. Anthropogenicactivities also have been playing increasingly impor-tant roles, especially in northeastern China.

3. Permafrost evolution during the Quaternary

3.1. Permafrost changes on the QTP

Many extensive, intensive and persisting glacia-tion–interglaciation permafrost shifts occurred dur-


ing the Quaternary, due to the rapid uplifting of theŽQTP and changing climates Li et al., 1989; Shi,

.1998 . In the Early Pleistocene, permafrost devel-oped only in high mountains; about 1.1–0.6 MaBPglaciers and permafrost developed extensively whenthe average elevation of the QTP rose to 3500 m.

The second glaciation maximum during the Qua-ternary occurred between 0.8 and 0.6 MaBP, with aMAAT about y12 to y48C, and permafrost wasextensively developed, especially in the western QTP.Ice-wedges, formed during the coldest stage of theLate Pleistocene, were found several places in the

Ž .Tianshuihai Basin 4900–5600 m in the westernŽ .Kunlun Mountains Li, 1987; Li et al., 1989 . Sand

wedges in the upper Yangtze River area formingabout 23.5"1.2 kaBP indicate a severe cold climateon the Cumar High Plateau in the interior of the QTPŽ .Guo, 1979 . Numerous cryoplanation terraces on theQTP and surrounding mountains were formed during

Ž .the Late Pleistocene Zhang et al., 1988 . Since thelast glaciation, the QTP has experienced multiplefluctuations in climate.

The interglaciation period following was a verywarm period, and permafrost almost completely dis-

Žappeared except in very high mountains Shi, 1998;.Shi et al., 1995 . During the glaciation periods from

330 to 200 kaBP, permafrost was continuously dis-Ž . Ž .tributed Shi et al., 1992 . Pan and Chen 1997

identified at least four periods of permafrost expan-sion during the past 150 kaBP. The permafrost area

Žduring the last glaciation maximum LGM: 16–32. 6 2kaBP was estimated at 2.2=10 km . The lower

limits of permafrost decreased from 1000 to 1500 munder a cooling of 6–88C. During the LGM, per-mafrost was widespread on the QTP, including Qi-dam Basin, Qinghai Lake area, Upper YaluzangpuRiver area and the surrounding mountainous regionsŽShi, 1998; Xu et al., 1984; Xu and Pan, 1990; Zhao

.et al., 1993a .The warm period in the Holocene occurred from

9.0 to 3.5 kaBP, when the MAATs were about2–58C higher, resulting in permafrost degradation.Sand wedges stopped developing about 9 kaBP,indicating the start of warming. During 8–3 kaBP,the climate was warm and comparatively humid, andpeat and paleosols were well developed as a resultŽ .Liu et al., 1997 . The warmest period was about the9–5 kaBP, when the MAATs were about 3–58C

higher; the megathermal occurred at about 6–4.5Ž .kaBP Zhao et al., 1995 . Therefore, the permafrost

on the QTP is largely relict and has been degradingsince the last glaciation. With the climatic fluctua-tions, the lower limits of permafrost on the QTPmoved up and down correspondingly, finally reach-ing their present positions. In the interior, permafrostexperienced local thawing and redeveloping. Duringthe Early Holocene warming, intensive and frequentflooding resulted in widely distributed gravel stratawith thicknesses of 1–8 m overlying sediment withpolygonal wedges. Permafrost north of the TuotuoheRiver thawed completely. During the following coldperiods, permafrost reestablished in those placesŽ .Qiu, 1982 .

3.2. Permafrost changes in northeastern China

The distribution of sand wedges, ice-wedge castsand other periglacial relics indicate that the southernlimit of permafrost stretched along 438N, with itsmaximum extent at 41–428N during the coldest stageof the Late Pleistocene. This suggests a cooling of

Ž . Ž7–88C during the LGM Fig. 2 Guo and Li, 1981;.Xu et al., 1989 .

During the Holocene megathermal, climatestended to warm, and the broadleaf forests becameincreasingly dominant. Based on the palynologicalevidence in southern Liaoning Province and the San-

Ž .jiang Plain, Guo and Li 1981 estimated that the airtemperatures during the Early Holocene hypsither-mal interval were 3–58C higher than at present. The08C isotherm of the MAAT had retreated northwardto the northern part of the present continuous per-mafrost zone in the Da-Xing’anling region. After themegathermal, permafrost extended southward again.

A group of well-preserved, inactive ice-wedgeswere discovered in the northern part of northeastern

Ž X X .China. The ice-wedges in Wuma 52845 N, 120845 Ewere formed during 10–14 kaBP, indicating a cool-

Ž .ing of 5–88C Tong, 1993 . If the MAATs wereabout 08C at the southern limit of permafrost distri-bution, which retreats about 18N with each 18C

Ž .increase in the MAAT i.e. the present situation ,permafrost might have reached 41–438N during the

Ž Xlast glaciation. The ice-wedges in Yitulihe 50832 N,X .121829 E were formed during the period from 4 to 2

ŽkaBP, mainly at about 2.7 kaBP Peng and Cheng,


Fig. 2. Traces of permafrost and its southern limits since theŽ .Pleistocene in northeastern China. 1 Present permafrost southern

Ž . Ž .limit; 2 southern limit of present continuous permafrost; 3Ž .southern limit of permafrost in the Little Ice Age; 4 southern

Ž .limit of permafrost in the Holocene hypsithermal period; 5Ž .southern limit of permafrost in Late Pleistocene; 6 inactive ice

Ž . Ž .wedges; 7 ice-wedges casts and sand-wedges; and 8 otherperiglacial phenomena.

.1990 , indicating a southward marching of per-mafrost during the colder stages after the Holocenemegathermal.

3.3. Permafrost changes in northwestern China

The belt of alpine permafrost in the TianshanMountains has changed its morphology many times

Žduring the Pleistocene and the Holocene Gorbunov,.1996 . At the end of the Pleistocene, the lower limits

of permafrost in the northern Tianshan in Kaza-khstan were 1200–1500 m lower than they are to-day, i.e. they were at 1000–1200 m in elevationŽ .Gorbunov, 1978 . During the Holocene, these altitu-dinal boundaries moved up and down alternatively.Relict permafrost is found in may places in theTianshan Mountains, Kazakhstan, suggesting a cool-ing of about 2–38C in the MAATs and a vertical

300–400 m falling in the lower limits of permafrostduring the Little Ice Age.

Climatic changes in the sources of the UrumqiRiver, Xinjiang, China have been comparatively mildsince the last glaciation and syngenetic permafrosthas formed as a result. At about 7 kaBP, the MAATwas 18C warmer than at present with permafrostlower limits at 3100–3400 m. The upper UrumqiRiver area was still periglacial during the hypsither-mal period. Buried, icy humus with an age of 7700–550 years, and a thickness of 7.68 m, suggests asyngenetic cryogenic origin of alpine permafrost in

Ž .swampy lowlands Zhao et al., 1993b .

3.4. SensitiÕity of permafrost in China to past cli-matic changes

The southern limits of permafrost distribution innorthern Europe have retreated 23–248 northwardsince the last glaciation and have shrunk 16–188

northward in North America. However, in northeast-ern China, there have been only 6–88 retreats. Thiscan be attributed to the combined influence of thestrong and persistent inversion layer of the atmo-sphere up to 1500 m in elevation, controlled by theSiberia-Mongolia Low Pressures and local geogra-

Ž .phy Fotiev, 1965; Fotiev et al., 1974 , in northeast-ern China. In western China, the lower limits ofaltitudinal permafrost have risen several hundred to

Ž .about 1000 m Xu et al., 1989 . In the meantime, inthe European Alps, the lower limits of the continu-ous permafrost belt might have risen more than 3000m during late glacial warming of at least 158C,accompanied by a nearly 10-fold increase in precipi-

Ž .tation Haeberli et al., 1993 . In North America, theroughly 1000 m shift in the lower limit of permafrostoccurrence, with respect to present-day conditions,suggests a minimum late-glacial warming of 6–108C.On the QTP, the amplitudes of climatic warmingsince the LGM were 3–108C and precipitation was1000–2000 mm. During the last glaciation, the tem-peratures were 6–88C lower than present, and thechanges of permafrost lower limits on the QTP since

Žthe last glaciation are estimated at 500–1500 m Shi.et al., 1995; Zhao et al., 1995 . In other words, the

periglacial environment in northern China has beenless sensitive to climatic warming, and permafrost on


Table 3Changes of the MAGTs along the QTH in 8C

Borehole JXG CK114 CK124-4 CK123-4 CK-7 K2956 No.1 CK123-7

Location Xidatan Taoerjiu Valley Basin Tongtian Cumar FHS BasinPermafrost zone NLM CrIPB SLM SFG RT CPZ CPZ IPZPresent MAGT 0.3 0.8 0.8 0.8 0.8 y0.9 y2.8 y1.0Rise from 70–90s 0.5 0.3 0.3 0.3 0.4 0.1 0.2 0.2

Ž . Ž . Ž .Note: northern lower limit NLM ; southern lower limit SLM ; continuousrisland permafrost boundary CrIPB ; seasonally frozen groundŽ . Ž . Ž . Ž .SFG ; river taliks RT ; continuous permafrost zone CPZ ; and island permafrost zone IPZ ; northern mouth of the Jingxiangu ValleyŽ .JXG . The MAGT here is defined as the mean annual ground temperature at about 15 m.

the QTP has experienced changes similar to thepermafrost in North America during the past climaticchanges.

4. Recent permafrost changes

4.1. Permafrost degradation on the QTP

As a result of climatic warming of about 0.3–0.48C during the past 40 years, based on permafrost

Žmonitoring and characteristic of winter warming Ma.et al., 1992 , extensive permafrost degradation on the

QTP has been interpreted and is expected in thefuture. This can be inferred from rising MAGTs,deepening in thaw depths, disconnecting and disap-pearing of island permafrost, increasing and expand-ing of taliks and the burying of permafrost.

4.1.1. Ground temperature rising in island per-mafrost zone

Monitoring along the QTH from Golmud to Lhasaindicates an increasing of the MAGTs of about0.3–0.58C in seasonally frozen ground, taliks, and

island permafrost zones, and about 0.1–0.38C in theŽ .continuous permafrost zones Table 3 .

Ž X X.Xidatan 35843 N, 94811 , at the 4480-m eleva-tion along the QTH, is located in the island per-mafrost zone near the northern lower limit of per-mafrost distribution on the QTP. The observation siteis set on the first terrace of a brook, where the soilsconsist of fluvial sands and gravel. The surface is dryand barren of vegetation. The maximum seasonalthaw depth at this position varies from 2.0 to 2.6 m.Drilling in 1983 indicated a permafrost bottom at24–25 m. As shown in Table 4, the bottom ofpermafrost rose to a depth of 20 m by 1993. TheMAGTs at depths of 12–20 m have risen 0.2–0.38C.Permafrost has been degrading upwards only. How-ever, at a site 4428 m in elevation, 1-km southeast ofthis Xidatan site, permafrost degradation both up-ward and downward has been detected. Drilling andtemperature readings in 1975 suggested a permafrost

Ž .layer at depths of 5–15 m Table 5 . The measure-ments in 1989 proved the existence of permafrost atdepths from 8 to 11 m, indicating a vertical decay ofpermafrost of at least 4 m, and a warming of 0.2–0.48C in the MAGTs.

Table 4Ž . Ž .Average July ground temperatures 8C at depths m at the Xidatan observation site

Depth: 0.4 0.8 1.6 3.2 4.0 6.0 8.0 10 12 14 16 18 20 23 26 29

1997 5.57 2.17 y0.30 y1.27 y1.28 y0.85 y0.55 y0.48 y0.34 y0.24 y0.11 y0.07 0.07 0.28 0.55 0.751996 6.81 4.01 y0.21 y0.60 y0.96 y0.72 y0.46 y0.50 y0.45 y0.26 y0.12 y0.12 0.03 0.24 0.48 0.711994 4.20 1.55 y0.87 y0.85 y0.85 y0.45 y0.40 y0.35 y0.07 0.00 0.25 0.40 0.551993 3.56 1.46 y0.36 y0.83 y0.86 y0.84 y0.29 y0.22 y0.18 y0.40 y0.14 y0.08 0.06 0.21 0.54 0.561992 4.03 2.21 y0.18 y0.68 y0.74 y0.74 y0.27 y0.24 y0.22 y0.42 y0.20 y0.09 y0.02 0.18 0.49 0.531991 1.20 0.42 y0.08 y0.99 y0.89 y0.87 y0.38 y0.34 y0.49 y0.48 y0.43 y0.43 y0.17 y0.18 0.23 0.27


Table 5Ž . Ž .Ground temperatures 8C at different depths m in Borehole CKIII-4 at Xidatan

Ž .Depth m : 1 2 3 4 5 7 9 11 13 15 20 25 30Date

89.05.25 y0.6 y1.3 0.0 0.0 0.1 0.0 y0.1 y0.1 0.1 0.3 0.4 0.5 0.879.08.05 6.8 1.2 0.2 0.1 0.2 y0.2 y0.1 y0.2 0.1 0.2 0.2 0.3 0.475.11.08 y3.8 y0.1 0.2 0.0 y0.1 y0.2 y0.2 y0.2 y0.2 y0.1 0.0 0.1 0.3

In the unstable permafrost zone, with a MAGTofy0.5–08C, permafrost has been warming andthinning rapidly. Permafrost disappearance also isstriking. Buried permafrost was detected at depths of11.4–16.0 m at Xidatan, near the northern lowerlimit of permafrost in 1960. The drilling at the sameplace in 1975 revealed no permafrost. Jingxian’gualso is located at the northern lower limit along theQTH. The bottom of permafrost has risen about10–15 m in the past 20 years. The MAGTs at depths

Žof 15–20 m have increased about 0.5–0.88C Table.6 . This was caused by thermal influence of intraper-

mafrost water available only after gradual downwardthawing of the upper permafrost layer created water-ways.

Liangdaohe is located at the southern lower limitof permafrost along the QTH. Permafrost was de-tected at depths of 3–8.5 m in June 1975. However,nine readings of ground temperatures afterwards re-vealed significant warming in 18 years, and a grad-

Ž .ual disappearance of permafrost Table 7 .

4.1.2. Ground temperatures rising in the continuouspermafrost zone

Ground temperatures at shallow depths in transi-tory and quasi-stable permafrost zones have beenincreasing noticeably. Ground temperatures at aborehole at Kunlun Pass also have increased 0.2–0.48C at depths of 6–15 m in the past 15 yearsŽ .Table 8 . This site is located at an elevation of 4700m, and is underlain by fluvial gravel, with a soilmoisture of 12–18%, above 2.5 m in depth, and bylacustrine sediments below with ice contents of 30–45%. The thaw depth reaches its maximum of 1.3–1.4 m in summer and the MAGT is y2.6 to y2.58C.Below the depth of seasonal change at 15–20 m, thepermafrost is 80–100 m in thickness.

At Borehole CK2956 on the Cumar High Plateau,in the interior of the QTP, ground temperatures have

increased about 0.3–0.48C at depths of 5–10 m. Theground temperatures at depths of 12–14 m haveincreased about 0.1–0.38C. However, those belowthe depth of 15 m have remained fairly stable be-cause of the underlying thick ground-ice layer. Theground temperatures in interior QTP, for example, atthe Fenghuoshan Mountains, also have been increas-ing. The ground temperatures at depths of 15–35 mat Fenghuoshan have increased 0.2–0.38C during the

Ž .past 35 years Table 9 .

4.1.3. Permafrost disconnectionThawed nuclei have been detected widely at Xi-

datan and Amdo along the QTH, and at Anyemaqenˆ ˆMountains, Qingshuihe and Huashixia along Na-tional Highway No. 214 in eastern QTP, indicating avertical disconnection in unstable permafrost. As aresult, permafrost distribution has changed signifi-cantly.

Climatic warming has caused a decrease of 10–40cm in the depth of seasonal freezing and an increaseof 5–30 cm in the depth of seasonal thawing, Thesehave resulted in the vertical disconnection of thepermafrost table and seasonal freezing depth. As aresult, thawed nuclei have formed extensively along

Table 6Ž .Ground temperatures 8C at Jingxiangu along the QTH

Ž .Depth m : 6 10 12 14 16 18 20 22 24Date

75.11.08 y0.2 y0.2 y0.1 y0.2 0.0 0.0 0.176.04.26 y0.3 y0.2 y0.2 y0.2 0.0 0.0 0.0 0.279.08.03 y0.4 y0.2 y0.2 0.0 0.2 0.3 0.4 0.7 0.885.08.05 y0.4 y0.2 0.0 0.1 0.3 0.6 0.9 1.089.05.25 y0.4 0.0 0.1 0.2 0.5 0.6 0.8 0.9 1.094.06.24 0.2 0.2 0.3 0.6 0.6 1.295.07.07 y0.3 0.1 0.2 0.2 0.5 0.6 0.896.05.14 y0.4 0.2 0.2 0.3 0.5 0.6 0.897.07.08 y0.2 0.1 0.2 0.3 0.4 0.6 0.8


Table 7Ž .Ground temperatures 8C in Borehole CK124-4 at Liangdaohe along the QTH

Ž .Depth m : 1 2 3 4 5 6 7 8 9 11 13 15 17 19Date

79.08.05 0.6 y0.1 y0.3 y0.1 y0.2 y0.2 0.0 0.2 0.3 0.5 0.5 0.5 0.7 0.884.08.07 y0.2 y0.3 y0.3 y0.1 0.1 0.1 0.0 0.2 0.2 0.7 0.6 0.8 0.7 0.989.07.26 0.7 0.1 0.1 0.0 0.1 0.1 0.2 0.2 0.3 0.6 0.7 0.8 0.9 0.894.07.05 0.0 0.1 0.1 0.7 0.5 0.5 0.6 0.8 0.8 0.7 0.8 1.0 0.995.07.01 y0.1 0.0 0.2 0.4 0.6 0.8 0.9 1.0 1.2 cable below 9 m was damaged

and no reading measurable.96.06.27 0.4 y0.1 0.2 0.5 0.6 0.8 0.8 1.1 1.297.07.06 0.4 y0.1 0.3 0.4 0.6 0.8 0.9 1.1 1.2

the edges of permafrost regions, where the per-mafrost table is now buried as deep as 4–7 m andwhere the seasonal freezing only reaches 2–3 m.

4.1.4. Shrinkage of permafrost areasIncreasing ground temperatures have thinned per-

mafrost about 5–7 m, or have thawed thin per-mafrost layers completely, resulting in the movingup of island permafrost boundaries. For example, thesouthern lower limit of permafrost along the QTHhas moved 10 km northward, whereas the northernlower limit has moved 3 km southward. In thevicinity of Mado in eastern QTP horizontal subtrac-tion of permafrost zones is 15 km along NationalHighway No. 214. As a result, the areal extent ofpermafrost on the QTP has been significantly re-duced during the past few decades. This is mainlyattributed to permafrost retreat since the 1970s. Thepreliminary estimate for the areal reduction of per-

6 2 Ž .mafrost is 0.1=10 km Wang, 1997 .According to the 1:100 000 island permafrost map,

Žcompiled in 1975, for the southern QTH with a.width of 2 km on each side of the QTH , the

permafrost area was 65 km2 in the counted area of320 km2, or about 20%. The permafrost areas were

divided into four groups according to geomorphicŽ .locations Table 10 . Recently, comprehensive inves-

tigations indicate that the permafrost area has de-creased to 42 km2, suggesting a reduction of 35.6%in the island permafrost area.

The rate of permafrost degradation differed geo-morphically. The most rapid permafrost shrinkingoccurred in the mountains and on the plains, whereasisland permafrost in the valleys and basins has beendegrading more slowly because of the dense vegeta-tion cover and rich ice content in the fine soils.

4.2. Permafrost degradation in northeastern China

Permafrost retreating in northeastern China isstriking, under a rapid warming, and has been in-creasingly affected by human activities. The southernlimit of permafrost in northeastern China has beenoscillating within a belt with the MAAT of "1.08C

Ž .since the Little Ice Age. Guo and Li 1981 esti-mated a southward march of 100–150 km in thesouthern limits during the LGM. There were onlyvery limited human activities in northeastern Chinabefore the 20th century; and the wildness were notdisturbed until the early 1900s. The natural environ-

Table 8The annual ground temperatures in a borehole at the Kunlun Pass Observation Site

Ž .Depth m : 4 5 6 8 9 10 12 13 14 15 16 18 20Date

1982 y2.9 y2.8 y2.8 y2.8 y2.8 y2.7 y2.8 y2.8 y2.6 y2.6 y2.61994 y3.1 y3.0 y2.9 y2.8 y2.7 y2.7 y2.8 y2.7 y2.8 y2.5 y2.6 y2.6 y2.61997 y2.0 y2.4 y2.4 y2.3 y2.3 y2.4 y2.6 y2.5 y2.6


Table 9Ž .Ground temperatures 8C in Borehole No. 1 at Fenghuoshan

along the QTH

Ž .Depth m : 8 9 10 15 20 25 30 35Date

62.08.31 y4.4 y4.1 y3.7 y3.5 y3.5 y3.3 y3.2 y3.067.06.03 y4.3 y3.9 y3.8 y3.5 y3.4 y3.3 y3.2 y3.080.08.30 y3.9 y3.6 y3.6 y3.5 y3.3 y3.2 y3.1 y3.084.06.30 y4.1 y4.0 y3.9 y3.5 y3.3 y3.2 y3.1 y2.889.06.30 y3.8 y3.6 y3.6 y3.3 y3.2 y3.1 y3.0 y2.894.06.30 y3.8 y3.6 y3.6 y3.3 y3.2 y3.1 y3.0 y2.995.06.30 y3.9 y3.8 y3.6 y3.4 y3.2 y3.0 y2.8 y2.896.06.30 y3.6 y3.5 y3.3 y3.2 y3.2 y3.0 y2.7 y2.897.06.30 y3.8 y3.6 y3.4 y3.2 y3.2 y3.0 y2.8 y2.898.06.30 y3.8 y3.6 y3.6 y3.3 y3.2 y3.1 y2.9 y2.8

ment was severely damaged in the 1930s–1940s,when most of the forests were wiped out. During the1950s–1980s, the forest coverage in the Xiao-Xing’anling Mountains again decreased sharply dueto deforestation for agriculture and construction. Asa result, permafrost degradation has been accelerat-ing due to the removal of vegetation and organic soillayers, forest fires, and the fact that the permafrost innortheastern China is a relict Eurasian permafrost indelicate balance with local environments.

Due to the strong differentiation of permafrostcharacteristics and climatic changes, permafrost de-grades much more rapidly near the southern limits ofisland permafrost zones with strong anthropogenicdisturbances. Most of the island permafrost close totowns, such as in Yakeshi, Jiagedaqi and Dayangshu,which was detected in the 1950s, has vanished. Theregions far from social centers also experienced sig-nificant degradation. At a site in the outskirts ofJiagedaqi, the permafrost table was lowered from 1.7m in 1964 to 6.0 m in 1974. There also is a forestrange in the Xiao-Xing’anling Mountains, where de-forestation and permafrost degradation are closely

related. Disconnected and double-layered permafrostareas are also widespread.

In the northern part of the Da-Xing’anling Moun-Ž .tains, the MAGT is low y4.2 to y1.58C and

permafrost is thick and subsequently stable. Also,anthropogenic influence is less significant. However,comparisons with the MAGTs in the HeilongjiangŽ . Ž .Amur region Gu et al., 1993 indicate a warmingof 0.7–2.18C in the MAGTs at depths in the lowlandwetlands. The active layer thicknesses also haveincreased 20–40 cm during the past 30 years. Thepermafrost table under architectural structures hasdeepened 2–10 m during the past 20 years. Thelower base of permafrost has risen about 1–5 m,mostly in human-affected areas. The transformationof permafrost thermal stability, expansion of taliksand the intensifying of some periglacial processes,such as thermokarsts, also can infer permafrostdegradation in northeastern China.

4.3. Permafrost changes in the Tianshan Mountains

Permafrost temperatures at a depth of 14 m haveincreased by 0.38C during the past 25 years near the

Ž X X .Jusalykezen Pass 43805 N, 76852 E; 3350 m , Za-iliysky Alatau, northern Tianshan MountainsŽ .Gorbunov, 1996 . In the meantime, the MAAT andmean summer air temperatures in the alpine Za-iliysky Alatau have risen by 0.68C and 0.98C, respec-tively, from 1938 to 1989. In the inner Tianshan, theMAGTs at depths of 15–20 m in two boreholes at

Ž X X .4000–4200 m 41830 N, 78810 E increased by anaverage of 0.28C from 1986 to 1992, whereas nochange was observed in other three boreholes. TheMAAT at 3614 m nearby increased by 0.58C from1930 to 1988. Sporadic permafrost near the lowerlimits of permafrost has disappeared during the lastdecade in the northern Tianshan of Kazakhstan. It

Table 10Ž 2 .Areal change of island permafrost in km in the southern section along the QTH

Topography Basin Valley Plain Mountains Island % In the totalpermafrost mapped area

1975 16.76 34.08 1.74 12.23 64.81 20.21996 10.20 25.60 0.82 5.10 41.72 13.1

Ž .Reduction % 39.1 24.9 52.9 58.3 35.6 7.1


has been predicted that the lower limits of per-mafrost will rise about 250–300 m, under a climaticwarming of 28C, by the year 2025.

Climatic changes in the upper Urumqi River inthe Chinese Tianshan Mountains have been compara-tively mild under a regional climatic warming. Per-mafrost is also much more stable there. The groundtemperatures were measured in five boreholes withdepths of 15–60 m and at elevations of 3300–3900

Ž .m during 1990–1996 Jin et al., 1996 . The tempera-tures at depths of 10–39 m show diversified trends.The temperatures at depths greater than 30 m have

Ž .been warming 0.018Cryear .

5. Response and feedback of permafrost in Chinato climatic warming

5.1. Modeling the response of permafrost to climaticwarming on the QTP

5.1.1. GIS-aided altitude modelŽ .Cheng 1983 summarized a 3-dimensional zona-

tion in the distribution of altitudinal permafrost,namely, a vertical, latitudinal and aridity zonationusing the method of curve fitting. It is a statisticalcorrelation between the lower limit of permafrostŽ . Ž .H and latitude w . Named an Aaltitude modelBŽ .Li et al., 1998 , it is a Gaussian distribution functionand can be expressed as:

2Hs3 650 exp y0.003 wy25.37 q1 428.Ž .

Because the Aaltitude modelB takes the lowerlimit as the mere criterion of permafrost distribution,

the digital elevation model of the QTP can be easilyused to calculate the lower limit in each grid. Then,the calculated lower limit of permafrost is comparedwith the altitude in the same grid to conclude if thereis permafrost in the grid.

The Aaltitude modelB has been applied to forecastthe response of permafrost on the QTP to climatic

Ž .change Li et al., 1998 . Because there are no cli-matic variables in the model, some assumptions were

Ž .made as follows. 1 That the Gaussian function thatdescribes the distribution of permafrost will not

Ž .change under a warming climate. 2 If the airtemperature increases 18C, the vertical geographiczones will rise at a certain height according to thelapse rate of air temperature, and the lower limit ofpermafrost will rise the same height. Therefore, arelationship can be established between the air tem-

Ž .perature rise dT and the increase of the permafrostŽ .lower limit dH : dHsdTrg where g is the lapse

rate. It varies with latitude and altitude on the QTP.The change in the permafrost lower limit was ob-tained based on the air temperature rise according tothis assumption, and to judge if there is permafrost in

Ž .each grid. 3 The areas of lakes, glaciers and desertswill not change significantly.

Based on these assumptions, and if only the airtemperature increase is taken into account, per-mafrost distribution on the QTP in the years 2009,2049 and 2099 can be forecast using the AaltitudemodelB. The simulation results indicate that for thementioned periods, if the present simulation result is

Žregarded as the baseline with a digitized area of6 2 .1.294=10 km , spatial distribution changes of

permafrost on the QTP can be obtained. Table 11shows the changes in permafrost areas and the re-

Table 11Forecast permafrost degradation on the QTP during the next 100 years

Temperature Permafrost Decreased Areas of predicted permafrost degradation6 2Ž . Ž . Ž .increase 8C area 10 km percentage %

0.51 1.190 8 around Qinghai Lake and Changdu; betweenSelingcuo and Namucuo Lakes

1.10 1.055 18 small permafrost areas around Yushu; relativelylow elevations in southern QTP, especially onboth side of 308N

2.91 0.541 58 northeastern QTP, except south ShuleMountains; east to 938N; and most parts insouthern QTP


gions of permafrost disappearance. The permafrostretreats more rapidly in the eastern and southernQTP, and on periphery mountains, than that in theinterior of the QTP.

5.1.2. Numerical modelsThe global average air temperature is estimated to

Žincrease about 1.0–3.58C by the year 2100 IPCC,.1995 . In the simulation of permafrost changes using

numerical models, it is assumed that the warmingwill be at an average rate of 0.048Cryear during thenext 50 years, and that ground surface temperatureswill have a warming trend similar to that of airtemperatures. Under a natural state, dynamic changesof the permafrost thermal regime can be approxi-mated by finite solution of differential equationswith active phase change boundary conditions.

Numerical solutions were carried out, by finitedifferentiation, for the computation of the changingtrends in the permafrost thermal regimes along theQTH under a warming climate. In order to reflect thegeneral strata on the QTP, two soil layers wereselected for the simulation. The amplitudes of groundsurface temperature were calculated from the recordsat representative meteorological stations on the QTP,and from the mean annual temperatures at the per-mafrost table.

The simulated results indicate that, under naturalsurface conditions, the thermal balance line betweenpermafrost and seasonally frozen ground coincideswith the 0.58C isotherm of mean annual groundsurface temperatures on the QTP. If the initial groundsurface temperature for simulation is 0.58C, signifi-cant ground warming will occur 25 years later. After50 years, substantially large river taliks will appearin the interior of the QTP. The starting time forground warming shortens to the present after theinitial surface temperature drops to y4.5 to y3.58C.Alpine permafrost in the southern QTP will largelyvanish. The areas with MAGTs of y0.4–08C willdominate on the QTP, replacing the dominance ofthe areas with MAGTs of y1.5 to y0.58C. Areaswith MAGTs less than y2.28C will shrink signifi-cantly.

If the MAAT rises about 0.58C within the next 20years, permafrost less than 10 m in thickness will

Ž .retreat Li et al., 1996 . Consequently, permafrost onthe QTP would shrink about 3–5%.

5.2. Forecasting response of permafrost in north-eastern China to climatic warming

The secular warming during the 20th century wasestimated at 0.78C in the Da and Xiao-Xing’anlingMountains in the northern part of northeastern China,and the southern limit of Eurasian permafrost has

Žretreated 20–30 km northward in China Zhou et al.,.1993, 1996 . It is predicted that the northward

shrinkage of the permafrost will be about 80–200km and the MAGT will rise correspondingly, if theair temperature increases 18C within the next 50years.

5.3. Forecasting permafrost degradation in Chinaunder a warming climate

If the permafrost retreats in northeastern andwestern China are considered together, the arealdecrease of permafrost distribution would be 5–7%in China within the next 20 years. If air temperaturesrise about 0.58C within the next 50 years, permafrostless than 30 m would be affected, and the arealextent of permafrost in China would decrease 12–16%. If air temperatures rise about 1.08C within thenext 20 years, marginal permafrost less than 15 m inthickness on the QTP would be disconnected, andthe permafrost area in China would decrease about10–14%. If air temperatures rise about 1.08C withinthe next 50 years, the thickness of quasi-stable andtransitory permafrost on the QTP would decrease10–20%, and the MAGT would increase about 1.08C.

5.4. Contribution of permafrost wetlands on the QTPto atmospheric CH , CO and N O4 2 2

Permafrost on the QTP feeds back to the climaticsystems in the form of thermal and moisture ex-change via phase change of ice and water, changes inpermafrost spatial distribution, and its influence onalbedo and evaporation. Additionally, wetlands inpermafrost regions on the QTP also contribute signif-icantly to the global budgets of atmospheric methane,carbon dioxide and nitrous oxide.

The total area of freshwater wetlands on the QTPis estimated at 0.133=106 km2. In order to studythe greenhouse gases potentials from the cold wet-lands on the QTP, the gas fluxes and other environ-


mental variables were measured at representativeŽ .sites at the Huashixia Permafrost Station HPS

Ž X X .35809 N, 98852 E; 3450 m from 1994–1997. Thepermafrost under these wetlands has been degrading,based on the measurements of ground temperatures

Ž .since 1990 Zhu et al., 1995 . On the basis of theseobservations, the annual fluxes of CH , CO and4 2

N O from the wetlands on the QTP were estimated2Ž .Jin, 1998 .

High methane fluxes, ranging from y19.4–347.2mg my2 dayy1, were obtained in wet alpine mead-ows. The peak methane fluxes occurred in May andJune during the spring thaw. However, episodicfluxes were observed in July. Based on the arealextent of freshwater wetlands, representative methanefluxes, and the number of thaw days, the averageannual strength of methane emissions was estimatedat 0.7 Tg, ranging from 0.69 to 1.05 Tg. The emis-sion centers were located at the sources of theYangtze and Yellow Rivers and on the Zoige Peat-ˆlands.

The observed CO fluxes in wet meadows from2

April to September averaged y1070 mg my2 dayy1,with a standard deviation of 7870 mg my2 dayy1.The episodic events in the flux series strongly af-fected average fluxes. The CO fluxes show strong2

variations at the four sites. The alpine meadowsappear to uptake CO at a rate of 1840–3050 mg2

my2 dayy1, but the aquatic ecosystems appear toemit CO at a rate of 207–315 mg my2 dayy1. The2

seasonal variation for the CO exchange between the2

terrestrial ecosystems and the atmosphere was verystrong. This study covered only the thaw seasons andcan give a rough estimation of CO flux only for the2

thaw seasons. Based on the monthly average flux ofy472 mg my2 dayy1 for the thaw season of 180days, the strength of CO exchange is estimated at2

about y11.3 Tg during the thaw season.The average and median N O fluxes were posi-2

tive at all sites during the thaw season, implying anefflux averaging from 0.39 to 2.72 mg my2 dayy1

from alpine wetlands. Spring thaw released trappedN O at the rate of 0–2 mg my2 dayy1. N O absorp-2 2

tion predominated in June, while N O emissions2

dominated in other months during the thaw season.The conditions in August and September diversified.Seasonality of N O emissions is important in esti-2

mating the annual strength. However, the observa-

tion at the HPS covered only the thaw season. Theecosystems at the observation sites can be dividedinto alpine meadow and aquatic systems. Alpinemeadows emitted N O at a rate of 2.29–2.72 mg2

my2 dayy1 ; aquatic systems had a flux of 0.37–0.39mg my2 dayy1. The average N O emissions of 1.442

mg my2 dayy1 gave fluxes during the thaw seasonand during the year of 259.2 and 311 mgmy2 ,respectively. The annual N O emissions from the2

wetlands on the QTP are, thus, estimated at 0.022–0.025 Tg.

6. Cold regions engineering and environmentsunder a warming climate

6.1. Cold regions engineering

Permafrost degradation directly affects the stabil-ity of engineering construction and facilities in thecold regions in China, and human activities haveaccelerated permafrost degradation. The roads andother facilities were constructed under the principlesof permafrost protection. Due to comparatively highground temperatures, they are undergoing dramaticchanges under a warming climate. Various counter-measures have been and are being taken continu-

Žously to adapt to the changing environments Huang,.1988; Jin et al., 1997; Wu et al., 1993, 1997 .

The most remarkable indication for a warmingclimate in China is the thickening of the active layer,

Ž .such as on the QTP Table 12 . The permafrosttables have been dropping since the 1980s and, in thevicinities of the lower limits, the amplitudes of theincreases in the thickness of the active layer aregreater than those in the interior, such as in theFenghuoshan and Tanggula Mountains. The thick-ness of the active layer under asphalt road surfaces is1.5–2.0 m greater than that under natural conditions,due to the alteration of surface albedo and evapora-tion. In most cases, heat accumulation in the roadbases resulted in increased thaw depths too great tobe frozen and, consequently, the transformation fromvertically connected into disconnected permafrost.Correspondingly, the southern lower limit of contin-uous permafrost has moved 10 km-northward undernatural states; that under the asphalt road surface hasretreated 15 km.


Table 12Ž .Changes of the thickness of the seasonally thawed depths m along the QTH

Location Asphalt road surface Natural state surface Permafrost type

1980s 1990s 1980s 1990s

Kunlunshan 3.0 4.2 1.0–2.8 1.8–2.8 soil-contained ice layerCumar River 3.6 4.0 1.0–3.5 2.0–3.5 icy and ice-rich permafrostWudaoliang 3.8 4.8 1.2–3.0 2.0–3.5 soil-contained ice layerHoh’xil 2.9 3.6 1.1–2.5 1.8–8.5 soil-contained ice layerFenghuoshan 2.8 3.4 1.1–2.2 1.3–2.5 soil-contained ice layerTanggula 2.2 3.0 1.1–3.2 1.5–2.5 ice-contained and-rich permafrostTaoerjiu 2.7 3.8 1.0–2.0 1.3–2.5 ice-rich permafrostAmdo 2.5 5.5 2.0–3.0 2.2–4.0 ice-contained permafrost

With the increasing thickness of summer thawdepths, thaw settlement and frost heaving have beenenhanced. The thaw settlement increased with in-creasing seasonal thaw depth during 1985–1990.The settlement in the sections with thawed nucleireached 60–70 cm, much greater than those withoutthawed nuclei. Based on a field survey in 1990, roaddamages caused by thaw settlement accounted for83% of the damages along the QTH.

Most of oil pipelines on the QTP were buried atdepths of about 1.0–1.5 m. Although no thaw settle-ment has been caused by the warm oil flows atpresent, warming permafrost is expected to threatenthe stability of the pipelines. For example, excava-

Ž X X .tions in the Kunlun Pass 35840 N, 94802 E; 4715 min September 1997 indicate that the oil pipeline, witha diameter of 168 mm and built in 1973 along theQTH, has induced a summer thaw depth of 140–150cm, whereas the nearby summer thaw depth reachedonly 90 cm. The bridges and water conduits havebeen damaged considerably by thaw settlement onthe QTP. The Muli and Tumen Coal Mines in Qing-hai Province have suffered great losses since 1965due to permafrost warming, and the consequent in-stability of slopes and landslides.

6.2. Cold regions hydrology

In western China, the cold and arid regions arehydrologically connected. The middle and down-stream oases and the regional economy are vitallydependent on snow- and ice-melt water from themountains in the upper reaches. The studies onarid-cold regions hydrology were and are being con-ducted in the Urumqi River and Yili River in the

Tianshan Mountains in Xinjiang, the Heihe,Shiyanghe and Shulehe Watersheds in the QilianMountains in Gansu Province, and the upper YellowRiver and Qinghai Lake in Qinghai Province. Amongwhich, the calibration of dynamic loss in precipita-tion in the mountainous regions is vitally important

Ž .for water balance studies Yang et al., 1992 . Studieson evaporation in alpine regions have achieved some

Žgood results Yang and Zhang, 1992; Zhang and.Maire, 1992; Zhang et al., 1992 . Impacts of climatic

changes on the cold and arid regions hydrology areŽexpected to be great in western China Lai, 1996; Lai

.and Ye, 1991; Lai et al., 1995 .Based on data from the Qilian County Meteoro-

Ž .logical Station 2590 masl , the MAAT has risen0.48C from 1950s to 1990s in the middle section ofthe Qilian Mountains. The increases of mean winter,autumn and summer air temperatures are 1.18C, 0.68Cand 0.28C, respectively. In the meantime, the springtemperatures have cooled 1.38C. It is expected thatthe elevation of the 08C isotherms of the MAAT willrise from the present 2900 m to 3200–3300 m in the

Ž .mid-21st century Cheng et al., 1997 . The forestarea, precipitation, surface runoffs, groundwater andglacier ice volume have decreased gradually. Alpinecryospheric components and forests are important inmaintaining the stability of water resources in west-ern China. As a direct result of the shrinkage of thealpine cryosphere, the stability of water resources inwestern China has been affected significantly sincethe 1950s. The boundaries among the deserts, agri-cultural zones, pasturelands and snowlines have beenmoving upward in elevation in the Hexi CorridorŽ .37–418N, 98–1048E .


Climatic warming can affect permafrost area hy-drology through warming ground temperatures andchanges in precipitation, evaporation and runoffs inalpine regions. Permafrost area hydrology is largelydetermined by heat-moisture conditions in the activelayer. In the Qilian Mountains at the northern edgeof the QTP, increasing thaw depths have cast greatinfluence on the stability of water resources in theHexi Corridor during the past 50 years, resulting ingradual soil moisture depletion, increased evapora-tion and consequently reduced runoffs. In 1991, theprecipitation in the alpine regions was 6% less thannormal, and the mean summer air temperature was18C higher than normal, resulting in a 35% reductionin runoffs in alpine grasslands, and indicating anincrease of evaporation during a warm and dry pe-riod.

6.3. Cold regions enÕironments in China under awarming climate

In cold regions, permafrost serves as an imperme-able layer for water infiltration, thus fostering soilmoisture in the active layer vital for the developmentof alpine meadows. The pasturelands dominated byCyperus are well-developed in permafrost zones andare very important for the economy on the QTP.However, due to the permafrost degradation, ex-tensive deterioration and desertification of the pas-turelands have been developing since the 1960s.Permafrost warming can be accompanied by eitherincreasing or decreasing precipitation. In the formercase, the increased precipitation can offset the loss ofsoil moisture due to the thickening thaw depths orthe disappearance of permafrost. Permafrost degrada-tion also has induced some changes in landscapes,and hazardous periglacial phenomena, such as slopefailures, solifluctions and thermokarsts, resulting indamaged vegetation, followed by accelerating soiland water erosion.

The desertification in permafrost regions on theQTP has been of concern recently. The sandy landsare mainly distributed in river valleys, lake depres-sions and on flat plateau surfaces, covered by exten-sive sand layers and sand dunes. The sand dunesdeveloped on the QTP are mainly semi-fixed andshifting, parallel to aeolian depressions, and fast

moving. The fine sand layers cover ground surfacesextensively with depths from several centimeters to 1m. The areas with sand cover have been expandingsteadily during the past few decades according toobservations along the QTH, indicating an accelerat-ing desertification under a warming and drying cli-mate.

Previous studies indicate that in the sections withaeolian deposits, seasonal thawing is greater, groundtemperatures are higher, and permafrost is thinner

Ž .than those without sand cover Huang et al., 1993 .Some sections with sand cover in the permafrostzone, especially on the margins of the permafrostzone, have evolved into taliks. For example, drillingon the northern bank of the Tuotuohe River indicatesthat permafrost is absent under sand dunes, whereaspermafrost is developed or has remained in consider-able thicknesses in adjacent depressions, forming astriped talik and island permafrost region as wide as10 km. In the Tuotuohe basin, taliks are largelylocated under large sand dunes 3–5 m in diameterand 5–7 m in height, where the drainage is good,and the MAGTs range from 1.28C to 2.18C under adry surface. By contrast, permafrost is developed or

Ž .has remained as a relict of a former condition insubsurface barren depressions with a MAGT ofy0.28C to 08C.

Ground temperatures under flat sand dunes aregenerally higher than under natural flat surfaces. TheMAGT at 18 m under a 1.6-m-tall sand dune, with adiameter of 20 m, at the Highway MaintenanceSquad 66 along the QTH, was 0.28C higher thanunder an adjacent sand-free surface. The permafrosttable under the sand dune was at 3.3 m, 0.6 m deeperthan under the adjacent area.

7. Conclusions

The extent of permafrost in China has experi-enced major shifts, and may have disappeared, ex-cept on very high mountains, during the Quaternary.Accelerating fluctuations of climate and permafrosthave been identified during the Holocene, and mostareas of permafrost in China now are relicts of coldclimates, and have been in rapid and extensivedegradation, especially during the past 40 years. The


climate on the QTP has been warming since the lastglaciation, significant warming has been observedsince the 1970s, and further warming is expected inthe future.

Wetlands on the QTP can emit substantial CH 4

and N O, and uptake CO at a considerable rate.2 2

This will contribute significantly to global carbonand nitrogen budgets and feedback to climatic sys-tems.

Permafrost retreat and degradation have causedmany problems in cold regions engineering and tothe environments on the QTP. These have made iturgently necessary to reconsider permafrost protec-tion principles for engineering construction and oper-ations, as well as for environmental protection. Oneimportant impact of permafrost degradation is onwater resources, which will be a key issue for theregional economies and environments in China.

Acknowledgements

This work is under the auspices of the NationalKey Project for Basic Research and CAS Project for

Ž .Tibetan Research KZ951-A1-204 and KZ95T-09 .

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Permafrost and climatic change in China