عنوان مقاله [English]
More than half of the world human population has been living in urban areas. Irregular urban growth is considered as a global issue; and it is predicted that more than 65% of the world population will live in cities by 2025. Rapid growth of urbanization not only increased number of cities and population size, it also accelerated their physical growth. The process has led to consequences for urban population health, environmental resources, climate and biodiversity. In some countries, rapid physical growth of cities has even surpassed their population growth rates, and this uncontrolled growth creates a phenomenon called the "urban sprawl" which is a complicated model of land use, transportation, and socio-economic development. Urban sprawl is a kind of urban development with a low, unordered and unorganized density. In this type of development, the urban land use model is changed; and further per capita urban land is available to people. Factors affecting the incidence of these phenomena in cities are among important aspects that should be studied in the field of urban sprawl. Many factors contribute to the particular pattern of urban development known as urban sprawl, e.g., consumer preferences for inexpensive lots, single-family detached housing, and for living in green low-density neighborhoods, and the wish for second homes. Existing studies investigated numerous factors and processes ranging from macro level to local and micro levels such as failure of capitalist system (macro level) or local farmers' willingness to sell their lands with the aim of urban landuse change (local level). However, weights of these factors, their importance, time priority, their cohesion, effectiveness and impressibility are still unclear in the urban development process. There are a few studies with the same procedures as the present research. Therefore, this study has investigated causes of urban sprawl with an emphasis on local factors in Gorgan City as one of central cities of Iran.
The present study is a descriptive-analytical and applied research. Data collection was based on the available documents about growth of Gorgan City and survey methods. Since the research had specialty-based nature and it was impossible to achieve desired results through traditional survey methods, statistical population of research consisted of two groups of experts in the research subject: 1) thirty experts who were highly specialized in the urban sprawl and urban development and working in this field in Iran; 2) One hundred local experts who were quite familiar with the study area and participating in development of Gorgan City. Sampling was conducted using the snowball and judgmental methods. Research period was from 1956 to 2016. Data analysis was also performed using one-sample t-test, factor analysis, Shannon's relative entropy, Moran’s global index, and Geary's global coefficient.
Results and discussion
Providing documents of urban development process, it became clear that the urban growth was completely external. Results of entropy, Moran and Geary's models indicated that there were two distinct models of urban growth: 1- Cluster growth in the northeastern, southern and southeastern regions, and 2- Urban sprawl with vacant lands between textures in the central, northern and northeastern regions. The most important factors of this phenomenon were then identified and they consisted of 36 variables including 9 macro and 27 local variables. Due to the inter-correlation of variables, 29 variables with 5 main factors were identified as follows: Inappropriate and uncontrolled urban land use; inefficiency of urban management in urban control; ecological segregation; resident’s preferences for marginalization; abundance of land; and issues and challenges of urban population. We performed the correlated analysis of urban sprawl factors. Accordingly, the inability of local management to control urban growth procedures specially outside the legal limits of the city was the most important cause of this phenomenon in Gorgan and it included the following factors: failure to prevent the farmland speculation; inability to cope with illegal land subdivision by people; inability to cope with marginalization; inability to control land use of urban limits; inability to supply lands according to demand; impossibility of utilizing development capacity of barren and endowed lands within the city limits.
Urban sprawl of Gorgan city was resulted from interaction of various factors with an emphasis on local factors. Despite the fact that each of existing factors played the roles in this case, they did not have the same weights and importance. Based on the evidence and results of the present research, it seems that some factors play key roles in this process and can act as productive factors of urban sprawl because unlike the American model, the urban sprawl of Gorgan as one of the northern cities of Iran is not resulted from the public prosperity or existence of vast areas for urban development, but it happens since the local institutions of urban management of Gorgan lack sufficient power to control urban growth procedures around the city and also surrounding villages. They also lack sufficient power to control land use and its type of use. These two factors, along with another two factors of the resident preferences to live in the suburbs and garden cities in addition to urban population problems will provide serious urban development challenges. Among these factors, the physical-spatial contradiction in urban view is the most important issue. In other words, the regions with good weather conditions will be vertically developed and join the surrounding villages, but development of low-cost districts of the cities is dispersed over the area. This type of development model may lead to internal development of city provided that urban limits are controlled and other requirements are met such as solution of barren and endowed land acquisition problems. Finally, the urban sprawl can be largely controlled by controlling main factors (mother) which are originated from local processes.