Metropolis Explosion and Sprawl of Tehran within the Framework of Urban Decline Theory

Introduction Urbanization is considered as a profound transformation in the economic and social life of mankind. Patterns, stages and processes of urban development have been studied by many researchers. Various ideas are emerged in this field. The theory of was introduced Urban Decline by Berg et al. (1982) in in four stages including urbanization, suburbanization, de-urbanization and re-urbanization. This model is based on demographic changes within urban areas and population changes in the metropolitan region. Urbanization stage occurs when the growth of the main areas surpasses the rings, while the daily urban system is growing. The suburbanization stage occurs when the growth of the rings surpasses the main areas, while daily urban system is still growing. The de-urbanization stage occurs when the growth of the rings is greater than the growth of the main regions, while the daily urban system is declining. The re-urbanization stage occurs when the growth of the main areas is greater than the growth of the rings, while the daily urban system is declining. The study of Tehran Metropolitan urbanization proved that"Metropolis Explosion" phenomenon and modern suburbanization are based on the intense political focus and service-industry activities followed by the imposed restrictive policies of the city.The objective of this stage is the growth of middle cities in the periphery of the Tehran Metropolis. Methodology Tehran Metropolitan Region is selected as the study area of this research. This research studies the process of explosion of the metropolis and the emergence of urban decline in the main city and urban sprawl as an objective reflection of the development of the city’s periphery from 1976 to 2016. This research has a retroductive strategy and fundamental in terms of purpose, and analytical in terms of its method.This research has applied meta-analysis method and has used secondary population data of the Center of Statistics as a measure of scale and information of outreach schemes. It has used the traditions of quantitative and qualitative method.To analyze the data, we have used the directional trends (Standard Deviational Ellipse), global and local Moran Spatial Correlation model, Hot Spot Analysis (Getis-Ord Gi*). We have used Shannon and Holdren entropy models in the ArcGIS10.3 to investigate the growth of the city in the studied periods. Results and discussion Resukts of population statistics (1976-2016) have indicated that Tehran has experienced an exponential growth since 1950s. This has been influenced by peripheral development policies. The survey of demographic data shows that the peripheral population of Tehran has experienced a growth from 14.73% in 1966 to 54.67% in 2016. Evidence suggests that Tehran Metropolitan region has experienced a Suburban expansion until 1986 with the growth of middle cities as its main feature, but from this time it has an onward Exurban development. This expansion (the completion of the second stage) is characterized by the emergence, development, and rapid growth of small cities. The results of the global and the local Moran Spatial Correlation models and the general Getis-Ord Gi statistics indicate the formation of several cluster patterns of the population outside the Tehran Metropolitan Region. The results of the Shannon model shows the increase of Shannon's value in the peripheral cities and development from the center to the periphery during the second (2000), third (2006) and fourth (2016) periods, while the main spatial development of the cities in the second and third periods (suburbs) has occurred in the second ring. In the fourth period (2016), the density of the Shannon coefficient has also reached the third ring (out of the suburban area). Based on the Holdren model, urban sprawl development has occurred in 25 of 43 cities with more than 30 percent in 19 cities. Conclusion The research findings indicate that "Tehran Metropolitan Region" has begun its modern-day suburban stage since the 1970s and after the 1990s it faced the process of de-urbanization (decline).The spatial representation of these two processes has been manifested in a sprawl. The results of the global and the local Moran Spatial Correlation models and the general Getis-Ord Gi statistics indicate the formation of several cluster patterns of the population outside the Tehran Metropolitan Region. The results of the Shannon entropy and Holdren models state that the development of urban areas has occurred in the second ring (Suburban) and the third ring (Exurban) since the 1990s. The result of this research suggests that the phenomenon of urban decline in the Tehran metropolitan Region follows the urbanization processes experienced in the American-European countries. The adaptation of the empirical findings of this study to Berg et al. (1982) illustrates that Tehran Metropolitan Region also follows the same pattern, and multiple stages of urban development and urbanization have emerged in this area. The findings of this research are consistent with the results of Berry (1970), Beale (1977), McCarthy and P. Morrison (1977) and Sternleib and J. Hughes (1977), Vining and T. Kontuly (1978), Hall and Hey (1978), Fielding (1982), Berg and et al. (1982), Saeid nia (1375), Nazari (2008), Zanganeh (1392), and Rajai (1394). Urban development processes in both developed and developing countries follow a fairly similar set of rules on a global scale. This is the reason behind the similarity of urban development spatial patterns.