تحليل الگوهاي پراكنده‌رويي شهري در منطقه كلان‌شهري تهران با تاكيد بر اثرات تفرق نظام تصميم‌گيري و كنترل رشد

Analysis of Sprawl Pattern in Tehran Metropolitan Region: with Emphasis on the Impacts of Decision-making and Growth Control Fragmentation

وجود تفرق سياسي و قلمرويي در شرايط فراهم بودن امكان برنامه‌ريزي كاربري زمين انحصاري و كنترل رشد محلي متفرق به پراكنده‌رويي توسعه مي‌انجامد. به زبان ساده قلمروهاي مديريت شهري (شهرداري‌ها) واقع در منطقه با تعيين محدوده براي شهر‌ها و كنترل ساخت‌و‌ساز موجب افزايش هزينه زمين و ساخت‌و‌ساز براي گروه‌هاي جمعيتي شده و با انجام برنامه‌‌ريزي كاربري زمين انحصاري (فقدان برنامه‌ريزي منطقه‌اي) موجب تقليل ذخيره مسكن قابل استطاعت درون محدوده خود مي‌گردند. از اين رو جمعيت سرريز (در ايران گروه‌هاي كم‌درآمد جمعيتي) براي يافتن مسكن و سرپناه مناسب شرايط اقتصادي خود به نواحي سرازير مي‌شوند كه زمين در آن ارزان بوده و در فقدان يا ضعف كنترل رشد، هزينه ساخت‌و‌ساز پايين است. تحقيق حاضر تلاش خواهد كرد تا مكانيزم عمل پراكنده‌رويي توسعه را در قالب بررسي الگوهاي رشد شهري در محدوده شهر‌ها، حريم و خارج از حريم منطقه كلان‌شهري تهران و نيز تغييرات رشد جمعيت پيش و پس از تاسيس شهرداري (ايجاد سيستم كنترل رشد) در اين منطقه را در طي چهار دوره مورد مطالعه از سال 1345 تا 1385 بررسي كند. يافته‌هاي تحقيق نشان داد كه در شرايط تفرق سياسي موجود، رشد سرريز در منطقه هميشه از نواحي داراي كنترل رشد به نواحي‌اي سرازير شده است كه كنترل رشد در آن‌ها ضعيف است.

The present research argues that the most challenging environmental regional problem in Tehran metropolitan region (TMR) is sprawl. According to our theoretical framework, in the case 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, and the areas with great accessibility to major service centers. After a while and due to concentration of population in unincorporated area, these centers are incorporated, municipality is established and growth control power is attained. 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 newly established conditions, spillover growth finds these new incorporated areas undesirable for development due to their relative high costs and constraint on development comparing with unincorporated outer areas of rural-urban fringe. The present research tries to study planning and management factors that cause sprawl development by examination of urban population growth trends in city limits, city buffers and outer areas that are not included within the two former planning and management territories. Another aspect of our study is focusing 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 performed in four period of time from 1966 to 2006 indicate that in the case of political and decision-making fragmentation, spillover growth always leaks from central and big cities with exclusionary planning and strong growth control and without 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 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 the whole metropolitan region was divided into three distinct areas (city limits, city buffer and outer areas of buffer), each with 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 a system of growth control) was another method for testing our hypothesis. A settlement with particular situation and in the absence of growth control, for example, experienced 65 percent growth in a 10-year period, while average growth rate in metropolitan region is 3 percent. The same settlement after incorporation and establishing municipality experienced only 5 percent growth in the same period of time. These processes of sprawl go hand in hand to extend urban development beyond central cities and into distant areas of the region. Control of this process of sprawl that works in a cyclic manner will not be possible in the case of political fragmentation in which there is no legislative body for coordinated regional spatial planning and governance. Accordingly, the mission of any kind of regional body and regional governance must be the regional growth management.