Table of Content

    25 January 2005, Volume 60 Issue 1 Previous Issue    Next Issue
    Climate Changes in the Tibetan Plateau during the Last Three Decades
    WU Shaohong, YIN Yunhe, ZHENG Du, YANG Qinye
    2005, 60 (1):  3-11.  doi: 10.11821/xb200501001
    Abstract ( )   PDF (1090KB) ( )   Save

    The Tibetan Plateau is one of the best places to study global climate change. Aridity or humidity status of land surface is an important outcome that has close relations with a set of climatic factors such as precipitation, temperature, solar radiation, relative humidity and wind, but the relationship between them is complicated. This paper calculated potential evapotranspiration by applying Penman-Monteith model which was recommended by FAO in 1998, and aridity index by Vyshotskii model to indicate aridity or humidity status of the Tibetan Plateau during the period 1971-2000. Then it analyzed the changing trends of observed climatic factors (temperature and precipitation) and calculated factors (potential evapotranspiration and aridity index), and showed the spatial distribution of aridity/humidity status over the Tibetan Plateau during the period 1971-2000. Trends calculated by linear regression were tested through Mann-Kendall test. Results of 77 meteorological stations on the Tibetan Plateau showed that the main trends of climate change are temperature rise and precipitation increase; potential evapotranspiration decrease and most of the areas was ascending to more humid status. Results suggested that aridity or humidity status cannot be presented only with precipitation.

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    Influences of Synoptic Variability on Spring Sand Storm Frequency in North China
    MAO Rui, GONG Daoyi, FAN Yida
    2005, 60 (1):  12-20.  doi: 10.11821/xb200501002
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    Based on the European Center for Medium-Range Weather Forecasts reanalysis datasets and the observed data for dust storms in North China, the authors investigated the relationships between dust storm frequency, monthly mean geopotential heights and synoptic variance in middle to lower troposphere for the period 1962 to 2000. The result shows that there is significant negative correlation between spring dust storm frequency and mean 500 hPa geopotential heights in mid-high latitude of East Asia, with correlation centers appearing in the Mongolia and Siberia. That suggests that this particular circulation pattern is likely to cause more cold air activities originating from the high latitudes and consequently result in frequent dust storms in North China. Weather process is the main reason for dust storm. The synoptic variance in East Asia shows evident year-to-year variations and long-term trends. There is significant relationship between synoptic variance and dust storm frequency. Their temporal changes are in phase. In addition, dust storm frequency is strongly correlated with the cyclone frequency (defined as the extremely low 850 hPa heights below the 10 percentiles) and the surface cold highs. It was found that the Northeast Low and cold surge activities of Mongolia and Siberia exert notable influence on dust storm frequency. Synoptic variance in East Asia shows a remarkable decreasing trend in 1962-2000 that explains a large portion of the decreasing in dust storm frequency. In addition, Arctic Oscillation may, in part, play a role in influencing the interannual variations of the synoptic variance and dust storm activities.

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    Assessment on Climate Change in China for the Last 2000 Years
    ZHENG Jingyun, WANG Shaowu
    2005, 60 (1):  21-31.  doi: 10.11821/xb200501003
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    The climate change in China was assessed synthetically for the last 2000 years, based on reviewing climatic change research literature published in the last 20 years. The main conclusions are as follows: (1) In the 20th century, a warming trend was clearly detected, but for eastern China the fluctuation magnitude was less than the maximum level, which occurred in the last 2000 years. (2) Precipitation showed the inter-centennial tendency having obvious spatial difference, especially in North China and south of the Yangze River, is opposite to the low frequency change trend. With respect to the entire change trend, before 280 AD, the climate was relatively wet but afterwards the climate gradually became dry. Furthermore, after 1230 AD, the climate was in the stabilized state of dryness. (3) The temperature change tendency in eastern China is consistent with western China but there were obvious differences in the magnitude and timing of the cold/warm epoch. (4) During the Medieval Warm Period, the climate was relatively dry in North China, while it was relatively wet in the south of the Yangtze River. In addition, the climate was relatively wet during the Little Ice Age in North China and the precipitation variation became greater in eastern China.

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    Palaeosol Developed and Paleoenvironment in the Guanzhong Plain during 420-350 kaBP
    ZHAO Jingbo
    2005, 60 (1):  32-40.  doi: 10.11821/xb200501004
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    The fourth paleosol (S4) which had changed into a residuum of the Brunhes Epoch (780,000 yr BP) at Shuangzhu in Chang'an, Koujiapo in Xi'an, Tianjiapo in Lantian and Hejiacun in Baoji developed over about 40 ka years. It consists of 4 horizons, the 1st one (uppermost) is a well developed reddish brown clay horizon (Bts), the 2nd is a dark yellowish brown weathering-cracked loess horizon (Cs) with red ferruginous clay films, the 3rd is yellowish brown weathering-cracked loess horizon (Cl) without the red ferruginous clay films, and the 4th is CaCO3 nodules horizon (Ck). In the Bts horizon, CaCO3 was leached away, Sr being trace element moved obviously and reached Ck horizon located at the bottom of the weathered profile, which indicates depth affected by weathering-leaching surpassed that of the Bts horizon and reached the lower boundary of the Cl horizon. In the Bts horizon, Fe2O3 and Al2O3 removed intensely also and into Cs horizon. In the weathered profile consisting of Bts, Cs and Cl, pH values are low, clay content is high, and Fe2O3 and Al2O3 were formed, which shows intense chemical weathering took place. The development of the fourth paleosol as a residuum suggests that a moist subtropical climate prevailed 420,000-350,000 yr BP in the southern part of the Loess Plateau in China. Its profile is Bts-Cs-Cl-Ck-C. When the paleosol developed, mean annual temperature and rainfall were about 16oC and 1000 mm respectively, about 3oC higher and 400 mm more than those at present in the Guanzhong Plain.

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    On the Spatial Pattern of Danxia Landform in China
    QI Deli, YU Rong, ZHANG Renshun, GE Yunjian, LI Jialin
    2005, 60 (1):  41-52.  doi: 10.11821/xb200501005
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    Danxia landform as a special geomorphic type is distributed in most parts of China. According to its spatial distribution patterns and regional differences, three major Danxia landform concentrated areas in China are identified in this paper. They are southeast area (including Jiangxi, Fujian, Zhejiang, Hunan and Guangxi provinces), the southwest area (the transitional zone of Yunnan-Guizhou Plateau and Sichuan Basin) and the northwest area (including Longshan mountain and both sides of the Huanghe River and its anabranches). The geologic and geographic conditions of Danxia landform and their differences of the three areas are analyzed. The Danxia geomorphologic landscapes, such as upright-shaped peaks, Danxia mesa, stone wall, cave and vertical cave, Danxia natural bridge, "a narrow strip of sky" and so on, are generally formed in the southeast area. The landscape of southwest area is characterized by Danxia escarpment face, waterfall and waterfall groups. The special landscapes in arid areas are found in the northwest area, for example, the mud-coating type, columniation type and board type of Danxia landforms, however there are more differences here than in the other two areas because of the complexity of the nature including the climate, running water, wind abrasion, the loessial cover and relevant elements and so on. Based on the tectonic uplift rates, regional structure of sedimentary red-basin, the fluvial process, weathering and biological processes, gravity and other internal gravitation and external processes in each Danxia landform area in China, this paper discusses the causes which control the differences and also explains the landscapes formation process and its mechanism.

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    The Distribution Patterns of Biological Soil Crust in Gurbantunggut Desert
    ZHANG Yuanming, CHEN Jin, WANG Xueqin, PAN Huixia, GU Zhihui, PAN Borong
    2005, 60 (1):  53-60.  doi: 10.11821/xb200501006
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    The biological soil crust, especially lichen crust, was developed well in Gurbantunggut Desert, the largest fixed and semi-fixed sandy desert in China. Together with vascular plant, biological soil crust becomes an important factors relating to sandy surface fixation. In this study, the reflectance of lichen-dominated biological soil crust was measured and used to develop a new index for detecting and mapping the crust distribution. We examined the feasibility of the index for Landsat ETM sensor by using radiative transfer model (6S) to simulate different coverage of the crust under different atmospheric conditions. Then, we applied the new index to Landsat ETM data of the Gurbantunggut desert to map the spatial distribution patterns of biological soil crust in Gurbantunggut Desert. The results, combined with field investigations, showed that the biological soil crust was mainly distributed in southern part of this desert, but became gradually sparse toward northern, western and eastern parts of this desert. The coverage of biological soil crust was estimated up to 28.7%. The species composition of biological soil crust varies according to different positions of sand dunes and different developmental stages of biological crust.

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    Contemporary Sedimentation Rates on Salt Marshes at Wanggang, Jiangsu, China
    WANG Aijun, GAO Shu, JIA Jianjun, PAN Shaoming
    2005, 60 (1):  61-70.  doi: 10.11821/xb200501007
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    The total area of coastal wetlands exceeds 5000 km2 in Jiangsu Province, China, but it has been decreasing rapidly as a result of intense reclamation activities. Two types of plants, Spartina angelica and Spartina alterniflora, were introduced successively into the Jiangsu coast, in order to protect the coastline from erosion and to increase the accumulation rate. 210Pb and 137Cs analyses were carried out for sediment samples from the salt marshes of Wangang, to derive the sedimentation rate, on the basis of an evaluation of the background values and factors affecting the enrichment of 210Pb. Analysis of a typical sediment column of the tidal flat shows that the absorption of 210Pb in the silt-dominated sediment is weak. Influences of storm events, bioturbation, material sources and analytical error also have an effect. As a result, some abnormal data points are present. These data were removed before the calculation of the sedimentation rate. The sedimentation rate was 3.3 cm a-1 on average. Based upon analysis of the 137Cs dating, the rate since 1963 was 3.1 cm a-1 on average, similar to the data by 210Pb dating and from previous studies.

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    Evaluation of Sediment Accumulation in Dianchi Lake Using 137Cs Dating
    ZHANG Yan, PENG Buzhuo, CHEN Jie, LU Junjie
    2005, 60 (1):  71-78.  doi: 10.11821/xb200501008
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    Based on the 137Cs activity and the specific geographical location of the Dianchi Basin, the 137Cs in the soil of Dianchi Basin and in the sediment of Dianchi Lake are derived from both the fallout of the world nuclear tests and that of China nuclear tests. Therefore, some sediment layers in special years, such as 1954, 1963, 1976 and 1986, can be identified by special distribution of 137Cs activity in the sediment cores. The mean annual accumulation mass of sediment per unit area (sediment accumulation rate) for a specific period can be calculated based on the accumulation mass of the various periods. The mean annual accumulations are diverse in different parts of the Dianchi Lake. But it is well agreed with the fact that sediment accumulation in the center of the lake is smaller than that of the lakeside. Then according to the shape of the lake, landforms of the lake basin, sources of sediment and other factors, Dianchi Lake is divided into five zones: central lake zone far from bank (I), central lake zone close to bank (II), western lake zone (III), eastern lake zone (IV) and southern lake zone (V). And using Geographic Information System (GIS), area of each zone is calculated. The total amounts of mean annual sediment accumulation of each zone for various periods is obtained by area of zone multiplying the sediment accumulation rate. The mean annual total amounts of sediment accumulations of the above five zones are 0.0572, 0.0925, 0.1249, 0.1095, and 0.0842 g/cm2a, respectively.

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    Analysis on Yellow River Surface Runoff Consumption
    ZHANG Xuecheng, LIU Changming, LI Danying
    2005, 60 (1):  79-86.  doi: 10.11821/xb200501009
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    Based on the summarization of annual surface runoff loss processes from 1956 to 2000, and current status of the surface runoff loss mechanisms of the large irrigated areas such as Ningxia in the upper, Guanzhong in the middle and irrigated area in the lower Yellow River, this paper analyzes the characteristics of the structural change in the basin runoff loss of the Yellow River, discusses the concept of the structural adjustment of runoff utilization quantity of the Yellow River, and explains the feasibility of putting it into practice. The analysis of the relationships among water supply, water utilization, water loss and water drainage will have much meaning in balancing supply-demand of water resources and the superior allocation scheme of water resource and so on. In addition, the basic data used in this paper to calculate the surface runoff loss etc. are the same as the data used for survey and assessment of water resources in the Yellow River Basin from 1956 to 2000.

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    A GIS Based Regional Torrent Risk Zonation
    TANG Chuan, ZHU Jing
    2005, 60 (1):  87-94.  doi: 10.11821/xb200501010
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    This paper explores the methodology for compiling the torrent hazard and risk zonation map by means of GIS technique for the Red River basin in Yunnan province of China, where is vulnerable to torrent floods. Based on a 1:250,000 scale digital map, six factors including the number slope angle, rainstorm days, buffer of river channels, maximum runoff discharge of standard area, debris flow distribution density and flood disaster history were analyzed and superimposed to create the torrent hazard risk evaluation map. Population density, farmland percentage, house property, and GDP as indexes accounting for torrent hazards were analyzed in terms of vulnerability mapping. Torrent risk zonation by means of GIS automatically was overlaid on the two data layers of hazard and vulnerability. Then each grid unit with a resolution of 500 m × 500 m was divided into four categories of the risk: extremely high, high, medium and low. Finally the same level risk was combined into a confirmed zone, which represents torrent risk of the study area. The risk evaluation result in the upper Red River basin shows that the extremely high risk area takes up 17.9% of the total inundated area of 13 150 km2, the high risk area is 45.9% of 33 783 km2, the medium is 25.2% of 18 563 km2 and the low risk is 11.0% of 8115 km2.

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    Climate Change of the Longitudinal Range-Gorge in Yunnan and Its Influence on the River Flow
    YOU Weihong, HE Daming, DUAN Changchun
    2005, 60 (1):  95-105.  doi: 10.11821/xb200501011
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    Based on the observed data of the flow in the longitudinal range-gorge region and the data of monthly precipitation and air temperature field in Yunnan, and using the statistics and wavelet transforms, the interannual climate change under the effect of the longitudinal range-gorge and its influence on the international river flows are investigated. The results show that the latitude variations of the high correlation centers between the monthly precipitation field and the international river flows are not significant due to the role of special underlying surface in the longitudinal range-gorge region, but the longitude variations are very significant. The annual precipitation of the Lancang climatic region is obviously greater than that of the eastern Lixian River and Yuan River regions, but the standard deviation of the annual precipitation is significantly smaller than them. The annual mean air temperature of the Yuan River region is lower than that of the western Lixian River and Lancang River regions, and the standard deviation of the annual air temperature is also smaller than them. Corresponding to the characteristics of the annual precipitation variations under the effect of the longitudinal range-gorge, the standard deviation of the annual flows of the Yuan River is also obviously greater than western Lixian and Lancang rivers. The barrier action of longitudinal range-gorge on southwest monsoon is greater, but on northeast monsoon is smaller. The annual precipitation variations under the effect of the longitudinal range-gorge are mainly on the smaller time scale, with the increase of time scale, the effect of the longitudinal range-gorge becomes smaller. The role of the longitudinal range-gorge in the annual air temperature variations is smaller than the annual precipitation variations. In recent years, the main characteristics of the annual precipitation variations in all the climatic regions are that precipitation tends to increase, under such an effect, the annual flow variations for the international rivers also tend to be great.

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    Areal Differentiation of Inter-provincial Migration in China and Characteristics of the Flow Field
    DING Jinhong, LIU Zhenyu, CHENG Danming, LIU Jin, ZOU Jianping
    2005, 60 (1):  106-114.  doi: 10.11821/xb200501012
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    The authors analyzed migration data of 2000 Census and discovered the areal differentiations of migration rates and the migration flow fields for different reasons in contemporary China. Internal migration in China reached a new era of high activity and high capability. The unbalance of migration rates among east, middle and west belts has been enforced gradually, proving that the "mid-belt subsiding" is a phenomena of society as well as economy. Within the three typical flow patterns, both convergence and radial migration pattern have developed which made the Peal River Delta a powerful convergence center, while convection between Northeast China and Shandong is disappearing. The Northwest is replacing Northeast as a new attractive area. If divided by Qinling-Huaihe and Heihe-Tengchong combined natural with human geographical lines, the migration field in China breaks into two "flow basins" of Southeast and Northwest. Priority of employment is getting greater in migration and market replacing planning acts the first driven force to migration and talent flow. The marriage migration directs mainly from southwest mountainous area to eastern rural area, which creates a "karst bride source" in Southwest China.

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    On Location Advantage Value of Residential Environment (LAVRE) in the Urban and Suburban Areas of Beijing
    ZHANG Wenzhong, LIU Wang, MENG Bin
    2005, 60 (1):  115-121.  doi: 10.11821/xb200501013
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    Firstly, this paper selects 7 factors such as service facility, natural environment, traffic situation and location condition to evaluate Location Advantage Value of Residential Environment (LAVRE) in the urban and suburban areas of Beijing. Secondly, it constructs a LAVRE model to evaluate LAVRE of different parts of in Beijing and analyze its spatial characteristics. Thirdly, based on data of average prices of lots of commercial housings, this paper sets up GIS-based spatial distribution of prices to analyze spatial relationship between LAVRE and housing prices, and the relationship between LAVRE and residential location selecting behaviors. Lastly, it draws conclusions as follows: (1) Integrated LAVRE has a trend of decreasing from the center of the city to its periphery, and shows the feature of circle configuration. This trend is similar to the spatial change of the commercial housing prices, which shows a fact that the spatial distribution of commercial housing prices is directly influenced by the residential environment. (2) As a whole, the difference of commercial housing prices between northern and southern Beijing is similar to that of LAVRE. (3) Spatial preferences of residential location selecting are affected by the location advantage of residential environment. That is, northern Beijing where LAVRE is relatively high is the concentrated area of residential location selecting, and the rate of residents who choose southern Beijing, where LAVRE is low relatively, is lower than other parts of Beijing.

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    Locational Study of Foreign Enterprises in Beijing Based on an Ordered Probit Model
    HE Canfei, LIANG Jinshe, ZHANG Hua
    2005, 60 (1):  122-130.  doi: 10.11821/xb200501014
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    Foreign direct investment has been a key driving force for China's urban development since the economic reform and opening up. Beijing is one of the favored locations by foreign investors. Foreign enterprises in Beijing have played a significant role in restructuring its production spaces and industrial compositions. Compared with their domestic counterparts, foreign enterprises are rational decision-makers and have more flexibility and freedom in choosing their locations. Governed by market forces, foreign enterprises are not randomly distributed within a city and their locational patterns are detectable. Based on data from the second census of basic units, this paper attempts to picture the spatial patterns of foreign enterprises in Beijing. Efforts are further made to investigate the locational behavior of foreign enterprises by incorporating firm-specific, industry-specific and location-specific factors in an ordered probit model (OPM). Empirical results show that foreign enterprises in manufacturing tend to agglomerate in the central city, but being diffused to the remote suburbs and having indeed promoted the industrial suburbanization in Beijing. Statistical results suggest that large and newly established manufacturing enterprises favor the suburbs while wholly foreign owned manufacturing enterprises and those producing multiple types of products tend to locate in the inner city. Industrial agglomeration pushes foreign manufacturers to the suburbs. Industry-specific factors play a crucial role in determining locations of foreign enterprises in Beijing. Those in resource and labor intensive sectors are inclined to locate in the suburbs while those in capital and technology intensive sectors are likely to favor the central city. The results have important policy implications for urban industrial restructuring in Beijing.

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    The Relationship between Urban Structure and Traffic Demand in Guangzhou
    ZHOU Suhong, YAN Xiaopei
    2005, 60 (1):  131-142.  doi: 10.11821/xb200501015
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    By using new techniques and model analysis, a case study on the relationship between urban structure and traffic demand in Guangzhou was carried out. The results show that there are certain relationships between the development of urban form and traffic demand. Firstly, the model of urban traffic ways is one of the reasons for shaping the urban forms. Secondly, the urban form directs the distribution of traffic demand. Finally, the factors of social and economic development have important impacts on both the urban forms and urban traffic demand, and their reciprocity. Meanwhile, there are also certain relationships between the urban structure and traffic demand. The balance of residents and industries is one of the factors affecting the selection of traffic ways and the distribution of traffic demand. At the same time, there are two models, e.g. demand oriented and supply oriented, concerning the relationship between urban commercial land use and traffic demand. The demand oriented one means that location is one of the most important factors affecting the commercial environment.

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    Dynamics of Urban Expansion in Xi'an City Using Landsat TM/ETM+ Data
    WU Hong'an, JIANG Jianjun, ZHOU Jie, ZHANG Hailong, ZHANG Li, AI Li
    2005, 60 (1):  143-150.  doi: 10.11821/xb200501016
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    In this study, we extracted urban boundary of Xi'an with supervised classification and Normalized Difference Barren Index (NDBI), respectively. Supervised classification is the most common method in obtaining land use/cover information. In this study, after data pre-processing, training samples were selected according to spectral features. Unlike conventional classification of land use/cover, in this paper, only two classifications of land cover were chosen, which were urban areas and non-urban areas. This could avoid the urban areas from the effects of too many classes, so that the urban areas could avoid being divided into too many classes. Then maximum likelihood classification was used to map the land use/cover of Xi'an. NDBI is an index like NDVI (Normalized Difference Vegetation Index), which can reflect the information of barrens on the ground. As the spectrum of built-up area is similar to barrens, NDBI is used to obtain urban built-up information. Like NDVI, it is defined as NDBI = (band5-band4)/(band5+band4). By comparing the two different methods, we find that the urban boundary derived from TM image using supervised classification is more accurate than that using NDBI, because the image of NDBI contains not only urban information but also barrens. What's more, it is difficult to distinguish them. Thus, we achieved urban expansion of Xi'an from 2000 to 2003 using supervised classification. Through the analysis of urban boundary of Xi'an in 2000 and 2003, it shown that during the three years, urban expansion in Xi'an was very quick. The urban area of Xi'an in 2000 was 253.37 km2, but in 2003 it reached 358.60 km2, an annual average increase rate of 12.3%. By analyzing related statistics of Xi'an, we drew the conclusion that the rapid urban expansion in Xi'an has been closely related to the fast growth of social capital assets investment and economic development of the Xi'an city since great development of western China. The statistic data show that during the three years from 2000 to 2003, the social capital assets investment rose from 23.2 billion RMB to 47.9 billion RMB, and the GDP of the city of Xi'an grew to 94.0 billion RMB from 64.3 billion RMB. In addition, the increase of population and the development of infrastructure like traffics are also important factors to it.

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    A Quantitative Assessment on the Quality of Life in Hangzhou Based on Landsat/TM and Socioeconomic Data
    WANG Weiwu
    2005, 60 (1):  151-157.  doi: 10.11821/xb200501017
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    By taking streets and towns as basic spatial analysis units, the quality of life (QOL) in Hangzhou is quantitatively evaluated by integrating principal component analysis and geographic information system overlay of ranked data layers. The socioeconomic variables such as population density, basic residential land price and percentage of college graduate are selected from socioeconomic data and the biophysical variables including percentage of built-up area, surface temperature (in oC) and NDVI value are extracted from Landsat/TM data. The results show that NDVI displays a strong negative correlation with percentage of built-up area (correlation coefficient r = -0.83) and surface temperature (correlation coefficient r = -0.63), so they are regarded as two main influencing factors of "green environment" quality. At the same time, there is also obvious negative correlation between NDVI and basic residential land price (correlation coefficient r = -0.66), percentage of college graduate (correlation coefficient r = -0.59) and population density (correlation coefficient r = -0.29). It means that "green environment" is still not the most important factor for high educated and high income families to choose living environment in Hangzhou, on the contrary, they would like to choose densely populated areas with convenient traffic conditions as their residence. Downtown of Hangzhou, that is, Shangcheng district, Xiacheng district and some units of Xihu district still belongs to higher QOL region (the first 20% of the evaluation value) and suburb appears lower QOL.

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    Modeling Urban Population Density with Remote Sensing Imagery
    LV Anmin, LI Chengming, LIN Zongjian, WANG Xingkui
    2005, 60 (1):  158-164.  doi: 10.11821/xb200501018
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    The population in the study region is the sum of the area of each habitation type multiplying its respective sampled population density. The population density of each habitation type is estimated. In some experimental region, there is mathematical relation among the area, the population density and its total population of each habitation type. The population density of each habitation type can be estimated via the mathematical relation. A new land use density method is proposed based on least square principle. The main idea is: First, habitation type is defined in the study region; and the boundaries of all the habitation types are lined out based on remote sensing imagery and the area of each habitation type are calculated; then mathematical models according to the population data of every sub-region are established; the best population density estimation of each habitation type is calculated with the least square principle when the number of sub-regions is more than the number of habitation types. The population estimation of any region can be calculated since the population density of each habitation type is known as well. The method need not sample the population density of each habitation type. The estimation workload of population density of each habitation type is low. The mathematical models are not influenced by random error of samples.

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    An Application of Bio-economic Household Model to Analysis on Man-Land Relationship Behavior in Ecologically Fragile Land of China
    SHI Minjun, WANG Tao
    2005, 60 (1):  165-174.  doi: 10.11821/xb200501019
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    Land degradation is one of the severe environmental problems in China. In order to combat land degradation, a soil conservation program has been introduced since 2000 to reduce soil erosion by converting slope farmland into forest and pasture. This paper represents the first systematic attempt to investigate the impact of the soil conservation program on land degradation in the Loess Plateau. The results indicate that the soil conservation program to convert slope land into forest or pasture is an effective way to combat soil erosion. However, a subsidy that is higher than profit from slope land use activity before conversion is needed to encourage farmers to join the conservation program. Relevant policies to encourage and assist farmers to raise livestock in folds with crops produced from fields as well as fodder and forage grass from the converted slope land might contribute to combat soil erosion. Increase in off-farm job opportunities may encourage farmers' households to reduce farming practices on slope land. This implies that policies to encourage ruralurbanization might contribute to combat soil erosion.

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