Potential Urban Hazard Zones of Shanghai, PRe

C. Nicholas Raphael Professor

Jinan Li Senior Programer

Department of Geography and Geology Eastern M ichigan University Ypsilanti, MI48197

2389 Timbercrest Ct. Ann Arbor, MI48106

92

ABSTRACT

Land-use data derived f rom large scale aerial images were used to determine po­tential hazard zones of Shanghai, Peo­ple's Republic of China. Using a GIS, nine cultural and physical parameters in one­kilometer2 pixels are identified, classified and mapped. A coefficient of urban haz­ard is calculated per square kilometer within the city. Of the 10 administrative municipalities, J inan and Luwang, in the central city, are determined as having high urban disaster potential. Natural hazards such as storm surges and subsi­dence in the delta complex have been rec­ognized and addressed . However, in view of increasing urbanization, urban hazard is yet to be adequately addressed.

KEY WORDS: land cover, Shanghai, urban environment, GIS, hazards, remote sensing .

INTRODUCTION

As the largest city in the People's Re­public of China, Shanghai has many ur­ban problems which create an environ­ment for potential natural and human hazards. Located on the deltaic plain of the Yangtze Jiang (Yangtze River), Shang­hai emerged from a small wa lled town to China's main entrepot (Fig . 1). In the early part of the nineteenth century the town had an area of 2.14 km 2 and a suburban region of 2.50 km 2 • Occupying this area was a population of some 250,000 people creating a density of 53,000 persons/km 2

(Schinz 1989). In 1995 the city's population was 12.5

million and by the year 2010 it is pro­jected to increase to 21.7 million (United Nations Population Division, 1993). The rapid population growth and transition of Shanghai from a modest town to China's largest and most productive industrial city has not been without problems. In­compatible urban land uses, high popu­lation densities, antiquated transporta­tion, and air and water pollution have created potential hazards.

This analysis identifies land use and land cover of Shanghai in order to iden­tify areas of potential hazard. If and when

Jiangsu

Province

HU I ~

31 0 ._. ';_')u"/ oJ ~.r. " ~~(/

.J .-''/ Shejiang

Province

FIGURE 1. Shanghai and the Yangtze Jiang deltaic plain.

major emergencies disrupt urban life, au­thorities must be prepared to offer a rapid and organized response. By mapping the land cover and weighing hazard factors, the areas of greatest environmental con­cern may be determined.

SHANGHAI'S ENVIRONMENTAL CONDITIONS

High population densities, traffic con­gestion, and pollution are contributing to a decaying infrastructure of Shanghai. Nearly 60 percent of the urban area is oc-

cupied by buildings or other structures. Although 30 million m2 of living space has been constructed since 1980 much more is needed (Binn, 1991). Narrow streets ac­count for traffic congestion in spite ofthe fact that only an estimated 170,000 trucks and automobiles are in the city. In the most crowded central part of the city, population densities are as high as 62,000 people per km2 (Shanghai Statistical Bu­reau, 1990). Clearly open space is limited and building density is high.

There are more than 8,000 factories and at least 7,000 industrial chimneys

93

which are sign ificant sources of th e near­ground air pollution (Yuqun Chen et al. 1988). Consuming 21 million tons of coal per year, industrial and domestic outputs emit some 314,000 tons of ash per km2

annually. Everyday, Shanghai creates 4.1 million tons of industrial liquid waste, 1.2 tons of residential liquid waste, 4,500 tons of residential sol id waste, 19,800 tons of industrial solid waste. The Huangpu Jiang flowing through the city has 229 days of dark color and foul odor in the year of 1988. Suzhou Creek, a smaller tributary joining the Huangpu Jiang in central Shangha i, is actually a sewage channel and a "biologicall y dead" water­way. Clearly water is a growing concern in Shanghai (Ward and Liang, 1995) .

NATURAL AND HUMAN HAZARD IN SHANGHAI

It is difficult to precisely determine po­tential urban hazards or evaluate risks in Shanghai . Historically, documentation of urban risk is related to natural hazards be­yond the control of the population such as typhoons and storms surges rather than populations densities and the mor­phology and conditions of the built envi ­ronment. Zenghao Qin and Yihong Duan (1992) , and Yamakawa (1990) determined that floods on the Yangtze Jiang and ty­phoons or tropical storms are by far the most common hazards in the delta region followed by plagues and famines. Dam­age by one intensive rainstorm on August 21 , 1977 totalled $5 million U.S. (Zenghao Qin and Yihong Duan, 1992) . More re­cently (August 7, 1991) a tropical storm flooded over 300 shops and factories in the city and displaced 2000 families. (Jae­fang Daily, August 7-8, 1991) .

Human risk factors related to disease, \\n~ and othet d\sastets ate teco<,;}nh.ed ma\n\'i \n the ?tess. \-\o""e\let, d\s\f\bu\\on ~ -a. ?i~\s -a. ~ ~ ~~ ~~

~ ~ ro ' rno ~ ~ \~ ,

against flooding and storm surges, dikes have been constructed and upgrading of protective structures are contemplated (N icholls, 1995). Although subsidence of the deltaic plain has been mitigated, at least four sites in the city, to include the Bund along the Huangpu Jiang, have sub­sidence rates in access of 10 mm per year (Mei-e and Milliman, 1996). Furthermore, air and water quality problems generated within the city pose continued risks.

METHOD OF ANALYSIS

The study area is approximately 320 km2 which includes the 10 contiguous dis­tricts of Shanghai (two remaining dis­tricts are physically separated from the central city). An efficient method of ex­amining and mapping such a large area is with remote sensing data bases to in­clude large scale aerial images. In this in­vestigation, infrared color aerial pictures at a scale of 1 :5,000 taken in 1988, were used to map the land cover of the city. Forty geography students from Shanghai Normal University were trained for one month in image interpretation tech­niques. Data obtained from the aerial im­ages record the nature of the land cover to include the built environment and nat­ural features. The imagery interpretation was then combined with field checks to verify questionable targets and update changes in land use/land cover. Details such as building heights and their uses were corroborated by the field work and available large scale maps or photo­graphs. Other information such as popu­lation data was also integrated for this st udy.

To analyze the land-cover data, an au­tomated overlay analysis was created and nine variables were simultaneously e\la\uated. 1hese ""efe bu\\d\f\<;} dens\\'I , bu\\d\f\<;} he\<;}h\, stteet dens\\'I, ""atet SUt-

"&2 , ~~' o .- ~\lI5. ;m.~<:i -a: 'Ca, ~\Sta~ \«)rn ' C'Ct\~ : ~ -a:

1\res ere fe?oned fesu\\\n<;} \n W. deaths and the loss ot '0,000 m"l ot \i\ling and ""ofk\f\1,! s?ace ~Jaefang Daily, A.u<;}ust 1 ,

\and use, and ?o?u\a\\on dens\\"'i. 'Cased on the image scale ot ':5000 , each pixel fe?fesents 2 ,50Q m2 on the <;}round. Since

~ • ~ :0:' ~ . ' ~-a: ~\)."\-

versifIed l and uses such as i ntegrated in­dustrial and residential land use contrib­ute to these latter problems. To protect

94

~\i~ ' ~~ are . ~~ , 'CO'

kilometer ot the city was composed ot 400 pixels. In total for the 320 kms2 area oi Shanghai , 128,000 pixels were examinee

and mapped by computer. Such a GIS technique is suitable for mapping such large and diverse urban areas. A GIS is most effective if its limitations are recog­nized (Coppock, 1995). Success will de­pend upon not only identifying and as­sessing the hazard but to communicate that issue to the appropriate authority and planners.

APPRAISAL INDICES

A key factor in the identification of di­saster environments is the decision of what land use/land cover parameters are selected. Unlike an assessment of envi­ronmental quality, an analysis of disaster background of a city is a geographic anal­ysis which includes such factors as hu­man activity, socioeconomic and regional relationships between people and nature. The indices are appraisal indices to as­sess the urban hazard of Shanghai .

Building Density (0)

Building density, the percentage of an area occupied by buildings in one square kilometer, is an important factor for con­sidering the condition of an urban envi­ronment. Theoretically, other things be­ing equal , the greater the distance between buildings, the safer the area is from chain reactions such as fire (Kartez and Lindell , 1987). Generally, a site with high building density will have more population, higher percentage of imper­vious land surface, lower street density, less vegetation and less open-water area.

A more impervious land surface, with a less vegetated area and less water area can result in a higher air temperature and ultimately a heat island. Duan Shaobo (1989) has noted that the average annual temperature of Shanghai is 15.70 C whereas adjacent rural temperatures are 1.50 C cooler. High temperature, and high relative humidity coupled with shared sanitation facilities can encourage the spread of infectious diseases. Diseases in turn could spread quickly because of the high urban population density.

Clearly when an emergency occurs, it is evident that the potential for disaster will be greater in more densely populated regions. For example, a fire may destroy

more houses or structures in highly clus­tered areas. In slum regions of Shanghai, the building density may be as high as 80 percent of the land cover. The problem is even more severe where streets are too narrow to allow fire trucks through and where access to water is limited. Further­more densely packed slum areas use coal for cooking. It has been determined that S02 and ash in the air is 0.249 gram m 3 in these areas (Mu Cui , 1988). It is conceiv­able that if a disaster such as fire, infec­tious diseases and/or air pollution was to occur in such a locality, the consequences would be dire.

Building Height (H)

When a large city is sited on diverse terrain such as in basins and valleys, the favorable environmental quality is found at higher elevations. Shanghai's deltaic plain has little topographical variation. However, buildings and structures or the built environment create high relief mor­phology in the urban complex. Generally the new buildings are much higher than the older ones. In the former French and British Concessions and in the original Chinese city center adjacent to the Huangpu Jiang, building height was gen­erally less than five stories. In recent years office buildings, hotels and multi ­story housing, frequently over 10 stories have been erected. There are more high buildings at the perimeter of Shanghai compared to the central part of the city (Fig. 2). This artificially created urban ba­sin which includes a mix of industrial and residential land uses prohibits the disper­sion of pollutants in the basin's atmo­sphere. (Li Jinan and Kuanghua Tao, 1994).

Street Density (5)

The statistical data of street area per square kilometer of total area provide some insights into the traffic conditions of the city. Traffic congestion frequently occurs in downtown Shanghai because streets and roads were not originally de­signed for motorized traffic. In fact, by vir­tue of numbers, bicycles and pedestrian traffic out compete cars. Thus, traffic ac­cidents even between bicycles are com-

95

L

o 5Km

I I

~ Huangpu River

FIGURE 2. Building heights in Shanghai .

mono In densely populated areas, the traf­fic arteries between houses are often less than one meter wide. When an emer­gency like fire occurs in such constrained areas, fire equipment is unable to access the site. Therefore, greater street density improves service accessibility.

96

Building height in meters

• >13

10 - 12

o 0- 9

Water Surface (W)

Surface water, to include ponds and streams, provide open space and help regulate urban air temperature. One of the most effective ways of controlling lo­cal climate is through the evaporation of water into the atmosphere. Consequen­tially introducing water into a built envi-

ronment creates a cooler summer season and a warmer winter season . Shanghai has nearly 30 km2 of open water in its ur­ban area (Fig. 3). However, the distribu­tion of the water area is uneven. Some regions through which the Huangpu Jiang and Suzhou Creek flow have 67 per cent water area per square km. However there is less than 1.3 percent water area in the core of the city.

Vegetation (V)

Evapotranspiration by plants and the occurrence of shade influence a region's humidity and temperature. Therefore, the percent area covered by vegetation has a significant influence on the built environ­ment. About 12 percent ofthe urban area of Shanghai is classified as having a veg­etation land cover (Fig. 4) . Most ofthe city actually has less than 10 percent vegeta­tive cover. In the central part ofthe city no more than two percent of the land cover is vegetated. Normally an area which has less vegetation has a higher building den­sity and poorer quality housing . The area with least vegetation is the Nansi District where each person has only 0.1 m2 veg­etation area and the house density is very high (Duan Shaobo, 1989). In areas of lower building density and higher street density such as the former French Con­cession, London plane or sycamore trees (Platanus acerifolia) frequently form a galleria over wide avenues. In outlying ar­eas the classification frequently includes intensively cultivated vegetable gardens. However, the evapotranspiration of water by plants helps to control and regulate humidity and temperature. Therefore, the amount of the area covered by plants in a city has significant influence on the ur­ban environment.

Impervious Land Surface (N)

The impervious land surface repre­sents ground that is paved or covered by hard materials such as concrete, pitch, tile or plastic. Impervious surfaces absorb and release heat much faster than water or vegetated surfaces and also have high run-off rates which effectively decrease evaporation and cooling . It has been es­timated that the mean annual runoff per

capita for Shanghai is 4,816 m3 whereas the corresponding index for the country which is predominantly rural, is 2,700 m3. In 1988, 156 kms2 of Shanghai was mapped as impervious land surface (Li Ji­nan and Kuanghua Tao, 1994). Further­more, the percentage of the impervious land surface in the core of Shanghai is as high as 75 percent.

Distance from City Center (D)

In the Orient, unlike North America the nearer to a city center, the denser the population . The center of economic activ­ity and residential land use/cover are dif­ficult to define because of the integration of land uses. Nanjing Road is often con­sidered the main street of the city. It is an economically important retail corridor for locals and tourists alike as well as a densely packed residential area.

Shanghai was laid out on a north­south and east-west grid pattern of eight kms2 in 1994. The city's grid was further subdivided into one km2 square cells which was in fact the basis ofthe GIS land use/cover inventory and analysis. The geographical center (i .e. "initial point" noted in the Congressional Township System in the U.S.) of Shanghai is located at the Peace Hotel adjacent to the People's Square. Key indicators of open space, open water (Fig. 3) and vegetation distribution (Fig. 4), reveal that the north, east and west outlying areas of the city have more open space than most other sites nearer to the city center.

Industrial Land Use (I)

In 1988, Shanghai had 1,500 large scale heavy industrial factories and 5,000 small manufacturers, including steel plants, chemical factories, cotton mills, and power plants (Fig . 5) (Yuqun Chen and Zhongmin Xu, 1988). Small factories are interspersed with the residential ar­eas with little if any open space. Such a site with both, a high percentage of in­dustrial and residential land use, is a po­tentially hazardous environment. Consid­ering air quality and the location of industries with respect to residential ar­eas, it is clear such land use within urban basins is unfavorable.

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l

Perccnt/Knf

• >23 0 5Km

I II 6.4 - 23

I2J 1.3 - 6.3

0 0-1.3

FIGURE 3. The distribution of open water area in Shanghai.

Population Density (P)

Although Shanghai is crowded, the population distribution varies from place to place. Since 1949 and especially in the last decades, many high rise apartments have been constructed at the perimeter of the city to accommodate the city's swell­ing population (Van Zhongmin and Tang

98

Jainzhong, 1990). However, the popula­tion density of the central part of the city remains high . In 1985, the highest popu­lation density of Shanghai was 65,000 per km 2 (Renxi Hu, 1988). Residents prefer liv­ing in the city center to the satellite towns outside of Shanghai . Here, daily life is much more convenient because of the many and cheap bus lines, easy and di-

o SKm

I I

~ Huangpu River

Percent / Km 2

• II o o

> 23

13 - 23

1.3 - 23

0- 1.3

FIGURE 4. Distribution of vegetation in Shanghai.

verse shopping options and recreation opportunities all of which outweigh the disadvantages of crowded living conditions.

APPRAISAL OF RANKINGS

To rank appraisal parameters is diffi­cult because they involve qualitative as well as qualitative evaluations. Sheehan

and Hewitt (1969) examined natural di­sasters between 1947 and 1967 on a world scale. They defined a disaster if one or more of the following criteria are met: a) at least $1 million damage; b) at least 100 persons injured; c) at least 100 people died. The criteria essentially analyzed the monetary value of the impact and sec-

99

o 5Km

I

~ Huangpu River

2 Percent/ Km

• (t1

EJ o

> 83

38 - 83

13 - 38

0- 13

FIGURE 5. The distribution of industrial land use in Shanghai .

ondly the intensity of the impact on the loss of human life.

Since the late 1960s, the Swiss Re (1990) has developed disaster thresholds. Based on its criteria a disaster occurs when; a) at least 20 people are killed or; b) when insured damage exceeds $16.2 million. This evaluation conceptually par­allels that of Sheehan and Hewitt. Both

100

models are subjective. A ranking model developed by the U.S. Environment Pro­tection Agency (1991) to evaluate ecolog­ical risk included factors such as the in­tensity and the scale of the impact but concluded that there was no generally ac­cepted model for assessing risks.

POTENTIAL URBAN HAZARDS

The nine parameters discussed above are used to relatively rank the potential urban hazards in Shanghai . Some of them are positive factors which mitigate an urban hazard, while others increase the probability of a hazard . The positive or high-value environmental factors are vegetation area{V), water area{W), dis­tance from city center{D) and street den­sity{S), whereas negative or low-value factors are building density {OJ, building height (H ), impervious land surface area (N), industrial land use area (I) and popu­lation density (P) . Therefore, the equation can be established as follows:

a = (O + H + N + P + I) - (1 ) (D + W + V + S)

where a is the relative hazard value. The higher the value of a the greater is threat of a disaster in a given region. Since the value of each nine parameters can be cal­culated for every single cell which repre­sents one square km on the ground, the hazard value of the number i cell is

ai = (Oi + Hi + Ni + Pi + Ii) - (2) (Di + Wi + Vi + Si)

Then the mean value of a for the whole city (n = 312) will be

_ 1 ~ . a = - ~ al

n (3)

The hazard potential of a pixel relative to the whole city is

mi ai

(4) a

where mi is the coefficient of urban haz­ard. Thus,

mi n* ai

(L ail (5)

In Shanghai some selected assess-

ment factors are more significant than others. Building density, population den­sity, and industrial land use clearly will re­sult in more severe impacts and are thus viewed as being twice as significant than other uses (e.g . building height) . Equally more open space (e.g. more water, veg­etation, and higher street density) will mitigate a potential urban hazard . Thus a two-tier ranking criterion was developed (Table 1). A parameter considered to be more significant was assigned a value of 2 whereas a less significant value re­mained at a value of 1. Equation (2) may then be modified:

Ai = (20i + Hi + Ni + 2Pi + 21i) (6) - (Di + 2Wi + 2Vi + 2Si)

Therefore, the coefficient of urban hazard of each pixel is

M n* Ai

Lr_1 Ai (7)

According to equation (7), the average coefficient of urban risk in Shanghai is 1.9255 and ranges between - 1.1141 and 4.9189. The result ofthe coefficient distri­bution is subdivided into five classes (Fig. 6) . Of the total area of 321 km2, 40 km2 of Shanghai has a negative value which suggests that 12 percent ofthe urban en­vironment is relatively better than the re­mainder of the city.

DISTRIBUTION OF URBAN HAZARDS IN SHANGHAI

Table 2 reveals risk coefficient and Figure 6 the area impacted by each class. As noted, 12.5 percent ofthe city area has the negative urban risk coefficient (M < 0) whereas 12.5 percent of the city area has a M value higher than 2.0000. About 48 percent of Shanghai's area has an M value of less than 1.0000, which means it has a relatively better urban en-

TABLE 1

Parameters Significant

Bd 2

Bh

The Weighted Parameters

R 2

Lp 1

P 2

Ld 2

o W 2

V 2

S 2

101

f;] 1

0 2 0 5Km

1m 3

11 4

~ Huangpu River • 5

FIGURE 6. The distribution of the urban risk coefficient of Shanghai.

vironment than the remainder (52%) of the city. The low risk areas are located at the city's perimeter and along selected reaches of the Huangpu Jiang.

In terms of distribution (Fig. 7), a higher urban risk value (M = > 2.0000) is concentrated in: (1) Luwang-Nansi dis­tricts; (2) Jinan-Zhabei districts and: (3) Hunkou-Yangpu districts. Among these, Luwang-Nansi, the oldest areas

102

of Shanghai has the highest risk. High buildings and high population density, slums, and less vegetation characterize Luwang-Nansi. The other districts, Jinan­Zhabei and Hunkou-Yangpu, have more area than the Luwang-Nansi districts, (13 and 11 km2 respectively) . Here industrial and residential land uses are interlaced. Unfortunately, these districts have the

Classes

1 2 3 4 5

0 I

2 I

TABLE 2 Classification of Urban Risk Coefficient in Shanghai

< 0 0.0001- 1.0000 1.0001 - 2.0000 2.0001 - 3.0000

> 3.0001

Area (km2)

40 114 126

40

Percent

12.5 35.4 39.3 12.5 0.3

M>Z.OOOO

~ >50

em 20-<t9

fZ2l 10-19

4 K" 0 - 9 I

0 < 1 ..

FIGURE 7. The distribution of urban hazard coeficiency in Shanghai. Districts: 1 = Puto, 2 = Zhabei , 3 = Hunkow, 4 = Yangpu, 5 = Changlin, 6 = Jinan, 7 = Huanpu, 8 = Xuhui , 9 = Luwang, 10 = Nansi .

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poorest air quality in Shanghai (Mu Cui, 1988).

Among the 10 analyzed administrative districts, Jinan and Luwang districts are at a greater potential for an urban disaster while Changlin District and Xuhui District have a lower hazard environment (Table 3) . Furthermore, most ofthe 40 km2 which have a lower M value «0) are distributed in the north (Yangpu District) , west (Chan­glin District) and south (Xuhui District) be­cause these regions have more open space and vegetation , and have less in­dustrial land use. Therefore, on the basis of the percentage of the coefficient of relative urban hazard which is more than 2.0000, the sequence of the districts from worse to best urban environment is Ji ­nan, Luwang, Huangpu, Hunkou, Nansi, Puto, Yangpu, Changlin and Xuhui .

CONCLUSIONS

With the use of large scale images nine parameters were used to map and deter­mine the distribution of potential hazard in Shanghai, PRC. Using a GIS the city was mapped in one km2 pixels. An auto­mated overlay analysis was created and the urban hazard factors were classified in each pixel. Of the 10 administrative ar­eas of Shanghai, Luwang-Nansi districts located in the central city have the highest potential for a disaster.

Physical hazards have been recog­nized and reasonably well addressed in Shanghai. Subsidence due to ground-wa­ter extraction and coastal protection from typhoons and storm surges have re­ceived attention and remedial action has occurred or is being contemplated partly because of global warming as related to rising sea levels. However, population of this megacity continues to increase and the threat of hazards continue to be in­adequately addressed particularly in the central city. The ability to make GIS as ef­fective as possible is the capability of translating the map products into action. Even well -trained manpower without good communication and cluttered or in­accessible transport networks may not be able to resolve Shanghai 's urban hazards.

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Coppock, J. T. 1995. GIS and Natural Hazards: An Overview from a GIS Perspective. In: Car­rara, A.; F. Guzzetti (eds.J. Geographic Infor­mation Systems in Assessing Natural Haz­ards. pp. 21 - 34. Boston, Kluwer Academic Publishers.

Duan Shaobo 1989. Some Features of Shang­hai's Physical Environment. Shanghai, De­partment of Geography, Shanghai Teacher's University, Shanghai.

Jaefang Daily; August 7-8, 1991 .

TABLE 3 The Urban Risk Coefficient Distribution in the Administrative Districts

of Shanghai

Area (km2) District's Area Percent of Mi Districts Class 1 Class 2 Class 3 Class 4 Class 5 (km2) (> 2.0000)

Puto 0 10 20 3 0 33 9 Zhabei 0 15 9 8 0 32 25 Hunkou 0 8 14 5 0 27 19 Yangpu 17 20 22 6 0 65 9 Changlin 9 11 15 0 0 35 0 Jinan 0 0 2 5 0 7 71 Huanpu 0 2 7 0 0 12 25 Xuhui 13 29 20 0 0 62 0 Luwang 0 1 3 4 1 9 56 Nansi 1 18 14 6 0 39 15 Total 40 114 126 40 321 100

104

Kartez, J. D.; Lindell , M. K. 1987. Planning for Uncertainty: The Case of Local Disaster Plan­ning. Journal of the American Planning As· sociation: 53(4): 487- 498.

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Yamakawa, S.; 1990. A Brief Chronology ofthe World Disasters. Science Reports Institute of GeoScience of Tsukuba Un iversity, 11 : 19- 37.

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Yuqun Chen; and Zhongmin Xi. ; 1986. Prob­lems of Urban Ecology and Economy in Shanghai. In: Chen, Y. ; (ed.), Theories and Practices in Urban Ecology and Economy. Shanghai, Shanghai Social Science Aca­demic Institute Press, Shanghai . (In Chinese).

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