Analysis of sprawl pattern in Tehran metropolitan region: with focus on impacts of decision-making and growth control fragmentation

Present research argues that the most challenging environmental regional problem in Tehran metropolitan region (TMR) is sprawl. According to the our theoretical framework, in the condition of political fragmentation, spillover growth always leaks from central and big cities (with exclusionary planning and strong growth control and lack of affordable housing) to unincorporated areas with weak growth control and cheap land available for development ,the areas also have great accessibility to major service centers. After a while and due to concentration of population in unincorporated area, these centers get incorporated and established municipality and growth control power. After establishing municipalities, local authorities prepare an exclusionary urban development plan in which there is no place for low-income and affordable housing. In the new established condition, spillover growth finds these new incorporated areas not desirable for development for their relative high cost and constraint on development comparing to unincorporated outer areas of rural-urban fringe. Present research attempt to study planning and management factors cause sprawl development by examination of urban population growth trends in city limits, city buffers and outer area that are not within the past two planning and management territory. Another aspect of our study focused on examination of population growth of cities and their changes before and after incorporation (establishment of municipality and creating system of growth control). Our examination that was done in four period of time from 1966 to 2006 indicate that in the condition of political and decision-making fragmentation, spillover growth always leaks from central and big cities with exclusionary planning and strong growth control and also lack of affordable housing to unincorporated areas with weak growth control and cheap land available for development. Main parts of these desirable sites for new development (mainly unplanned) are villages and rural area that present cheap lands, weak growth control and also desirable access to services delivered in adjacent central cities. Our research demonstrated that there is a considerable difference in growth rate of settlements within city limits and outer areas with weak growth control. In a detailed examination whole metropolitan region was divided into three distinct areas (city limits, city buffer and outer areas of buffer) each one have different growth control imposed on urban developments. Examination of population growth of settlements and their changes before and after incorporation (establishment of municipality and creating system of growth control) was another method for testing our hypothesis. A settlement in particular situation and in the lack of growth control, for example, experience a 65 percent growth in a 10 years period, while average growth rate in metropolitan region is 3 percent. Same settlement after incorporation and establishing municipality experience only 5 percent growth in the same period of time. These processes of sprawl go hand to hand to extend urban development beyond central cities and into distant area of region. Control of this process of sprawl which works in a cyclic manner will not be possible in the condition of political fragmentation in which there is not any body for coordinated regional spatial planning and governance. Accordingly, the mission of any kind of regional body and regional governance must be regional growth management.