Qingke Wen

Urban expansion in China and its spatial-temporal differences over the past four decades

The urban expansion process in China from the 1970s to 2013 was retrieved based on remote sensing and GIS technology. With the latest zoning method used as reference, annual expansion area per city, urban expansion type, and fractal dimension index were employed to analyze the Chinese urban expansion characteristics and its spatial difference from the aspects of urban expansion process, influence of urban expansion on land use, and urban spatial morphological evolutions. Results indicate that 1) under the powerful guidance of policies, urban expansion in China went through six different stages, and cities in the eastern region entered the rapid expansion period the earliest, followed by cities in the central, northeastern and western regions; 2) cultivated lands and rural settlements and industrial traffic lands were the important land sources for urban expansion in China; the influence of urban expansion on land use in the eastern region was the strongest, followed by the central, northeastern and western regions; 3) urban spatial morphology tended to be complex and was directly related to the adopted spatial expansion mode. Infilling expansion became the main urban expansion mode in the western region first, then in the central and northeastern regions, and finally in the eastern region. This study establishes the foundation for an in-depth recognition of urban expansion in China and optimization of future urban planning.

Spatial differences of coastal urban expansion in China from 1970s to 2013

As the ‘economic engines’ of China, coastal cities have developed and expanded considerably since the 1970s. In this study, information on the urban expansion process of Chinese coastal cities from the 1970s to 2013 was retrieved. Through the analysis of stage characteristics, spatial expansion modes, influences on land use, centroid shifts, and spatial morphological evolutions, the spatial differences of coastal urban expansion were revealed. Results indicate that 1) the expansion stages of southern coastal cities are more complex than those of northern coastal cities, and the expansion ranges and speeds of the former are far higher than those of the latter; 2) the spatial expansion of southern coastal cities mostly adopt a single mode, whereas northern coastal cities mostly adopt a mixed mode; 3) significant spatial differences in the occupations of different land sources exist between the south and the north along the coastline; 4) the centroid of coastal cities tends to migrate toward the coastline, and the centroid shift distances of southern coastal cities are clearly higher than those of northern coastal cities; and 5) the spatial morphology of southern coastal cities tends to be compact, whereas that of northern coastal cities tends to be loose. Policies have a powerful significance in terms of guiding urban expansion and its spatial differences in coastal cities. Urban expansion in coastal cities will encounter new opportunities and challenges under the guidance of new types of urbanization strategies.

Classification of Grassland Types by MODIS Time-Series Images in Tibet, China

Tibet is one of the five largest pasturing regions of China. Grassland classification is significant for its utilization and protection, but few correlative studies have been done in Tibet due to its rugged natural conditions, which make it difficult and time-consuming to conduct extensive field measurements. The remote-sensing technique is helpful for grassland classification in such regions. In this study, high temporal resolution of a moderate resolution imaging spectroradiometer (MODIS) is used to construct temporal profiles of enhanced vegetation index (EVI) during the grass growth period in Tibet. By dividing the large study area into individual regions based on altitude and latitude, we classified the grasslands of Tibet into six types-meadow steppe, typical steppe, desert steppe, alpine meadow steppe, alpine typical steppe, and shrub herbosa. Based on the 1:500 000 scale maps of Chinas grassland resources, the validation process indicates an overall accuracy of 68.02 %, and a Kappa coefficient of 0.52. Land managers are provided with maps and area values of each grassland type in Tibet in 2005. In addition, regional average EVI reflect the relative biomass of each types of the grassland, which will provide evidences for coordinating plans for grassland developing. MODIS_EVI provides a simple and rapid method to classify the grassland in regions that are hard to reach, which offers an effective means of investigating biological resources on a large scale.

Extraction of basic trends of urban expansion in China over past 40 years from satellite images

If urban sprawl is to be avoided in China in the next ten years, it is not only crucial to understand the overall history, current status, and future trends of urban expansion there, but also these differences, and this is presently lacking. In this study, remotely sensed images with approximately 30 m spatial resolution were used to quantitatively assess the spatial and temporal patterns of urban expansion of 60 Chinese cities (1973–2013). Urban-expansion-process curves of the cities studied were drawn using annual expansion area as an indicator. Curve similarity analysis generated four basic process modes of urban expansion in China. These included cities that: 1) peaked around 2004 and then decelerated; 2) peaked around 2010 and then decelerated; 3) showed sustained acceleration, and 4) showed continued deceleration. Four basic process modes represented cities under different levels of development stage. Geographic location was found to be the most related characteristic to urban expansion process. Regional development policies at the national level in each region also showed highly temporal consistency with fluctuation characteristics of urban expansion process. Urban characteristic such as population size and administrative level were not found to be significantly related to urban expansion-process modes. Understanding the basic process-mode categories well is extremely important for future regional-balance planning and development of macroeconomic policies.

Spatial and temporal variations of coastlines in northern China (2000–2012)

This study examined the spatial distribution of the continent coastline in northern China using remote sensing and GIS techniques, and calculated the fractal dimension of the coastline by box-counting method, with a time span from 2000 to 2012. Moreover, we analyzed the characteristics of spatial-temporal changes in the coastline’s length and fractal dimension, the relationship between the length change and fractal dimension change, and the driving forces of coastline changes in northern China. During the research period, the coastline of the study area increased by 637.95 km, at a rate of 53.16 km per year. On the regional level, the most significant change in coastline length was observed in Tianjin and Hebei. Temporally, the northern China coastline grew faster after 2008. The most dramatic growth was found between 2010 and 2011, with an increasing rate of 2.49% per year. The fractal dimension of the coastline in northern China was increasing during the research period, and the most dramatic increase occurred in Bohai Rim. There is a strong-positive linear relationship between the historical coastline length and fractal dimension (the correlation coefficient was 0.9962). Through statistical analysis of a large number of local coastline changes, it can be found that the increase (or decrease) of local coastline length will, in most cases, lead to the increase (or decrease) of the whole coastline fractal dimension. Civil-coastal engineering construction was the most important factor driving the coastline change in northern China. Port construction, fisheries facilities and salt factories were the top three construction activities. Compared to human activities, the influence of natural processes such as estuarine deposit and erosion were relatively small.

Urban expansion in China and its effect on cultivated land before and after initiating “Reform and Open Policy”

Urbanization in China has expanded at an unprecedented speed since the declaration of “Reform and Open Policy” and presented many challenges. Unbalanced regional development, appearance of super megacities and concomitant problems, and conflicts between urbanization and cultivated land protection are three critical problems that Chinese urbanization has to face. To develop new plans for foreseeable future urbanization in China, it is critical to understand the evolving history of cities across China. This study maps urban expansion of 60 typical Chinese cities based on large amount of remote sensing data and the labor-intensive image interpretation method, in order to understand the history of urban expansion from the 1970s to 2013. Results showed that area of cities expanded 5.23 times compared to their area in the 1970s. Urban expansion in China accelerated three times (1988–1996, 1999–2006, and 2009–2011) and decelerated three times (1997–1998, 2007–2008, and 2012–2013) over the 40 years. The urban area of South China expanded most significantly 9.42 times, while the urban area in Northeast China expanded only 2.37 times. The disparity among different administrative ranks of cities was even greater than (3.81 times) the differences among different regions. Super megacities have been continuously expanding at a fast rate (8.60-fold), and have not shown obvious signs of slowing down. The proportion of cultivated land among the land sources for urban expansion decreased to a small extent in the 1990s, but cultivated land continues to be the major land source for urban expansion. Effective future urbanization needs controlling the expansion scale of large cities and reasonably developing medium and small cities, as well as balancing regional development.

Regularity and causes of grassland variations in China over the past 30 years using remote sensing data

Grasslands, one of the most widespread land cover types in China, are of great importance to natural environmental protection and socio-economic development. However, grasslands are facing threats of gradual decline; therefore, an accurate quantitative study of dynamics of grasslands on a national scale may provide significantly theoretical relevance for an understanding of natural resources conditions in China. We used moderate-to-high resolution remotely sensed data and applied an index and method of spatio-temporal analysis to reveal the regularity of spatio-temporal variations in the grasslands from 1980s to 2010. We further applied the dynamic matrix to examine the cause of variations. The results indicated that the grassland area is continuing to decline. What’s more, the reduction rate exhibited an upward trend in near years from 2008 to 2010. Sixty per cent of the reduction distributed in northern and western China; however, the significance of the grassland reduction in eastern China was obviously higher. The main reason for grassland loss is the reclamation of cropland; however, a policy that returns cropland to grassland has effectively slowed the rate of gradual decline in the total grassland area. In addition, there is a high level of consistency between the variation trends of grasslands and relevant national policies.

Progress towards sustainable intensification in China challenged by land-use change

China is experiencing rapid land-use change and shifts in farm management. However, the interactive effects of these drivers on cropping system sustainability are unclear. Here, we evaluate spatio-temporal trade-offs among crop production and five key environmental indicators, including land use, water consumption, excess nitrogen and phosphorous use, and greenhouse gas emissions in China. From 1987 to 2010, as crop kilocalorie production increased (+66%), so did the total environmental impact of all indicators (+1.3–161%) except greenhouse gas emissions (−18%). Concurrently, environmental intensity—impact per kilocalorie produced—decreased for all indicators (−51–−13%) except excess phosphorus (+57%). Despite substantial loss and displacement of cropland to urban expansion, counterfactual scenario analysis indicates that farm management explained >90% of changes in crop production and environmental impact. However, cropland is expanding in regions of relatively high land and irrigation intensity. Although efficiency gains partly compensated for increased environmental pressures, continued geographic shifts in cropland could challenge progress towards agricultural sustainability in China.China’s agricultural output is growing rapidly, but the environmental impacts are unclear. This study finds this impact has risen, but much more slowly than output due to improved farm management, though ongoing shifts in cropland location may challenge this development.

City size distribution and its spatiotemporal evolution in China

Based on the National Land Use/Cover Database of China (NLUD-C) in the end of the 1980s (the 1980s, hereafter), 1995, 2000, 2005, and 2010, 665 cities were selected to study the size distribution and its changes of urban lands in China. In this study, the spatiotemporal evolutions of urban land size distribution as well as the influence of administrative-level on these cities were explored by combining urban spatial positions and administrative-levels. Results indicate that: 1) City size distribution using urban lands was more practical and reasonable than using non-agricultural population. 2) In the 1980s, cities with ascending urban land rank were centralized in Eastern China, specially the Changjiang (Yangtze) River Delta, the Zhujiang (Pearl) River Delta, and Beijing-Tianjin-Hebei region. Cities in Central, Western, and Northeast China mainly indicated descending urban land rank. 3) The transfer of national development focus resulted in cities with ascending urban land rank becoming evenly distributed nationwide; however, this trend was slightly centralized around Chengdu, Chongqing, and Wuhan in different periods. 4) During the 1980s to 2010, the proportion of cities with ascending urban land rank in provincial capitals, municipalities, and special administrative regions (high-level cities, hereafter) was consistently higher than those in prefecture- and county-level cities except for 2005–2010. The ranks of the majority of the prefecture- and county-level cities were mainly descending, supported by ascending; the proportion of cities with unchanged rank is small. This study breaks through the bottleneck of traditional research in the area of city size distribution by examining urban land replacing the non-agricultural population. The current study also provides scientific explanation for the healthy and reasonable development of urban land as well as the coordinated development of population urbanization and land urbanization.

The changing patterns of cropland conversion to built-up land in China from 1987 to 2010

Over the past few decades, built-up land in China has increasingly expanded with rapid urbanization, industrialization and rural settlements construction. The expansions encroached upon a large amount of cropland, placing great challenges on national food security. Although the impacts of urban expansion on cropland have been intensively illustrated, few attentions have been paid to differentiating the effects of growing urban areas, rural settlements, and industrial/transportation land. To fill this gap and offer comprehensive implications on framing policies for cropland protection, this study investigates and compares the spatio- temporal patterns of cropland conversion to urban areas, rural settlements, and industrial/ transportation land from 1987 to 2010, based on land use maps interpreted from remote sensing imagery. Five indicators were developed to analyze the impacts of built-up land expansion on cropland in China. We find that 42,822 km2 of cropland were converted into built-up land in China, accounting for 43.8% of total cropland loss during 1987–2010. Urban growth showed a greater impact on cropland loss than the expansion of rural settlements and the expansion of industrial/transportation land after 2000. The contribution of rural settlement expansion decreased; however, rural settlement saw the highest percentage of traditional cropland loss which is generally in high quality. The contribution of industrial/transportation land expansion increased dramatically and was mainly distributed in major food production regions. These changes were closely related to the economic restructuring, urban-rural transformation and government policies in China. Future cropland conservation should focus on not only finding a reasonable urbanization mode, but also solving the “hollowing village” problem and balancing the industrial transformations.