Driving Mechanisms Of Differentiated Urban Growth Rates In The Urban Fringe Area Of Nanjing

Urbanization is a significant aspect of global change and has a profound impact on urban ecosystem’s structure, function and dynamic. With the accelerated process of urbanization, the urban landscape usually shows complex pattern characteristics, so quantitative studies of the spatial and temporal dynamics and the driving mechanism contributed to a better understanding of the process of urbanization and its ecological effects.The landscape dynamics always have significant spatial heterogeneities. One of the important aspects is the differentiated urban growth rate. Urban fringe is the most active location in the process of urbanization where most urban growth occurs. Concentrating on the researches about differentiation of urban growth rate and the driving factors is an effective way to clarify the driving mechanism. Although the studies on driving mechanism increase gradually, the driving factors’relative effects strength and variation tendency at varied time periods and scales need to be further researched.As one of four major cities along the Yangtze River and the western hub city of Yangtze River Delta, Nanjing has experienced rapid urbanization process which is highly representative. To better understand the driving mechanisms of urban growth, we investigated the changes of the settlements in the urban fringe area of Nanjing and studied the driving mechanisms of the spatial differentiation of urban growth rates at multi-scales using the1998,2003and2008Landsat TM images. The results from spatial analysis and generalized linear models showed that:(1) The distribution and growth rates of the urban settlements varied significantly by location and time period. Settlement coverage in the study area increased continuously between1998-2008, but the growth rates slowed down. And the locational differences of settlement coverage and growth rates presented a declining tendency. We found that the settlement growth in Nanjing showed significant multi-axial spatial characteristics, the regions where grown faster were along the east (Qi Xia-Xian Lin) southeast (Jiang Ning),north (Pu Kou) and southwest (He Xi)(2) Settlement growth in the urban fringe area was influenced by a variety of factors, which depended on the spatial and temporal scales of interest. In1998-2003, the main influencing factors were mostly represented as water coverage, number of bus stops, nearest distance to the main roads and forest coverage. In2003-2008, the influencing factors included nearest distance to the main roads, public green land and number of bus stops.(3) Throughout the study period, transportation accessibility and the quality of living environments had influences on urban growth rate at all study scales, but their specific factors were scale-dependent.(4) By comparison, we found that transportation accessibility generally had the highest relative importance in influencing urban growth, and we can speculate the expansion of the urban edge is guided by the city’s transport system. The negative influences of urban infrastructure and public green land reflected the constraint of growing space. Such constraining effect only occurred at a small scale in1998-2003, while turned to be significant at both small and large scales in2003-2008.We studied the driving mechanisms in urban fringe area of Nanjing, and found that settlement growth in the urban fringe area was influenced by a variety of factors, which depended on the spatial and temporal scales of interest. The results reveal the importance of traffic accessibility in urban expansion, contribute to deepen the understanding of spatial and temporal rules of growth as well as landscape dynamics in urban area, and provide theoretical references for rational planning and sustainable development. In the future research, the social and economic factors should be considered for more comprehensive driving mechanisms, and it is necessary to establish the predictive model for practice.