Urban Carrying Capacity (UCC) as a Benchmark for Sustainability Assessment Modeling and Policy Making of Urban Spatial Structure: Case study; Shiraz City

Cities are occupying more and more surface area of the planet every year, and to survive, consume more natural resources, and the other hand their emissions of waste, sewage, and carbon and greenhouse gases are increasing. But can the geographical context of cities be able to load and accept this level of development? Today, Environmental problems are the most important issue in the cities of developing countries, especially in Iran. The main purpose of this study is to introduce sustainability assessment model and policy making of urban spatial structure based on urban carrying capacity. Is the development of the spatial structure of Shiraz as the largest metropolis of the southern half of the country is coincident with regional and extra-regional functions with the geographical carrying capacity and spatial carrying capacity and has led to the development of a sustainable spatial structure or not? It seems that Shiraz is far from the indicators of a sustainable city.

This research is descriptive-analytical in terms of nature and method and because the results can be used to improve models and provide solutions in the field of urban development programs, it is a type of applied research. By examining different methods of assessing carrying capacity and by examining and matching the methods of evaluating the concept (urban carrying capacity) with the features and characteristics of the geographical context of Shiraz and also considering this basic concept in geography that places have unique properties. In explaining and selecting indicators and constructive factors, urban carrying capacity was used, and the best evaluation method was selected and compiled in the form of an analysis model according to the conceptual model and the features and characteristics of the spatial structure of Shiraz. After this stage, by field study and perception of the spatial structure of Shiraz and also collecting the required data for each of the indicators and factors of the conceptual model, the Sustainability of the spatial structure of the city was analyzed using Vensim software. In the end, according to the obtained results and using the opinion of experts and experts in urban planning, as well as interventors in the field of services and urban management familiar to the metropolis of Shiraz (including 15 people, 10 of whom have Ph.D. in the fields of urban planning and urban development and urban management, 5 people are senior experts in the these fields; five people are working as university faculty members, and the other ten people are working in the municipality and of Roads and Urban Development administrations) to determine planning priorities and provide the best solution and the solution for the development of the spatial structure of Shiraz in relation to the urban bearing capacity was discussed

The results of the model showed that the current development trend of Shiraz is completely out of urban carrying capacity and is contradict with the principles of sustainable development. To change the current trend, first, the economic policy of job creation was used. The results showed that this policy has the most impact on the model and has led to economic prosperity and increased GDP, but over time and with a delay, it leads to issues such as traffic, pollution, migration, water shortage, green space destruction, housing problems and so on. In order to mitigate these problems, simultaneous implementation of environmental policies will be inevitable. For this purpose, policies were adapted such as strengthening the culture of reducing per capita waste production and encourage the separation of waste from the source, car ownership reduction policies, and increase public transport capacity, increasing the rate of wastewater purification, with development of municipal wastewater collection infrastructure; reducing per capita water demand for green space, by increasing irrigation efficiency supply of water from purified water, reduce per capita household water consumption; completion of the water supply project from Dorodzan dam, in order to increase urban carrying capacity and contribute to the sustainable development of the spatial structure of Shiraz.

This research with an environmental approach and in order to achieve sustainable development in the urban planning process, provided a model to assess the carrying capacity of the urban environment, to be a basis for measuring the sustainable development of the spatial structure of the city. Since achieving an acceptable level of quality of life for citizens is the ultimate goal of urban planning, this quality can not be achieved except by using the resources and capacities of the environmental and the geographical context in which the city is located. If the process of using resources has a logical and principled course, achieving quality of life will be accompanied by sustainable development. On the other hand, if the use of resources and development load is more than the capacity of the environment, environmental sustainability is in danger. Knowing that the development process of the spatial structure of Iranian cities, especially Shiraz, is far from sustainable development patterns, this study tried to make the view of urban development more aware of the carrying capacity of the geographical context of Shiraz. The proposed model can be used as a basis for decision-making process of planning, development and management of Shiraz city, and in preparing development and development plans of the city, as well as strategic development plan of the city, decision-making institutions, including roads and urban planning, the municipality and the city council.