تحلیل الگوهای توسعۀ فیزیکی شهرهای ایران با توجه به متغیرهای جمعیتی، طبیعی و کالبدی

Introduction
Urbanization is one of the most important human phenomena creating enormous impacts on the environment at local, regional and global scales. Although urbanization in the form of land-cover occupies less than 2% of the Earths land surface, there is plentiful evidence that human disturbance due to urbanization has significantly altered the natural landscape.
Cities are currently home to nearly half of the world population and over the next 30 years most of the two-billion people of global population is expected to occur in urban areas. In the developing world, Urban sprawl is the common characteristic of many fast growing cities across the globe that consumes agricultural lands around the cities and has pressure on natural environment.  In the first half of 20^th century, the majority of people were living in rural areas and cities had a slow growth. However, after mid 1950s due to the improvement in medical conditions as well as rural urban migration, it is faced with rapid population growth in urban areas. Improvement in the socio-economic conditions, especially increase in the private car ownership in the following decades, led to the low density of physical expansion of many cities in the country. This paper attempts to examine the status of Iranian cities based on two main patterns of continuous and discontinuous physical development and seek for the association of major social and environmental factors related to growth patterns of urban areas in the country.
 
Methodology
A descriptive analytical method has been employed in this research. The main source of data for the study has been driven from Google Earth images and Google Maps as well as the results of General Census of Iran from 1956 to 2006. In this research, the growth pattern has been studied for all cities with population over 5000 in Iran. The attempts have been made to associate these patterns with main social and natural variables such as population size, annual population growth rate, density, area, city plan, elevation and regional climate pattern. A Chi Square analysis has been used to find the association between city growth models and selected social and natural variables.
 
Results and Discussion
The results of this research indicate that 413 cities out of 689 cities over 5000 people (59/9%) had continuous physical growth and 276 cities (40/1%) discontinuous growth. To describe the physical growth pattern, we did a Chi square analysis and tried to find their possible association with the existing physical patterns with a number of social and environmental variables. The following table summarizes the outcome of Chi square analysis with selected variables (Table 1).
 
Table 1. Summarization of the outcome of Chi square analysis




Variable name


Chi Square
(X²)


DF
(df)


 (sig)


Pierson/Kendal
Correlation
(R)




population class


19.466


5


0.002


-0.033




City area


28.161


5


0.000


-0.196




Population density


19.322


3


0.000


0.183




Pop growth rate (10 yrs.)


8.177


4


0.085


-0.021




Pop growth rate (20 yrs.)


1.811


4


0.771


-0.004




Pop growth rate (50 yrs.)


4.004


4


0.405


-0.030




Elevation


13.431


6


0.037


0.072




اRegional climate


21.251


5


0.001


-0.071




 
Our analysis has revealed that there is an association between the population size of the cities and their physical growth patterns in a way that most large cities (over 500 thousands) have discontinuous physical growth pattern while most small and medium size cities have continuous physical expansion. The ratio of discontinuous physical growth pattern for cities between 5 to 24 thousands is 40%, cities between 25 to 49 thousands 45%, cities between 50 to 100 thousands 31%, and cities between 100 and 500 thousands 34%. 
Our study also depicts that there is a significant relationship between physical pattern and the area of the cities. While small and medium sized cities have more continuous physical growth, most cities with large area size (over 5000 hectares) have discontinuous growth pattern.  There is such a relationship between urban density and physical growth pattern.  Our data indicates that over 45% percent of the discontinuously growing cities have less than 50 persons per hectares, while over 80% of the cities with more than 100 persons per hectare has continuous growth pattern.
To find any relationship with urban physical pattern, we calculated urban population growth for the three time periods of 10, 20 and 50 years.  In contract with the discussed variables, none of the population growth rate for the three periods revealed any significant association with physical growth pattern in Iranian cities.
Among the environmental variables, two variables including elevation and climate were examined with respect to the physical patterns of the cities. Data findings indicates a correlation between elevation and city growth pattern in a way that the cities located at very low elevation (around Caspian see shores) tended to have more discontinuous growth pattern than those located in other areas. In contrast, the cities located at higher elevation especially above 1000 meters sea level are tended to have more continuous growth pattern. There is also an association betweenclimate type and growth pattern.Our data also indicated that the cities located in Moderate Caspian climate (Caspian Sea Climate) have more discontinuous physical growth while those located in other climates, especially semiarid and mountainous climate, have mostly continuous physical growth.   
 
Conclusion  
This study examined the status of Iranian cities in terms of their physical growth patterns and their associations with main social and environmental variables.  In this research, all cities over 5000 inhabitants were examined based on two major physical patterns of continuous and discontinuous growth. Then, their relationship was tested with the selected variables using a Chi square analysis. Main results indicated that about 60% of Iranian cities has continued growth pattern and 40% has discontinuous pattern. The findings of this research have also indicated that four main social variables of population size, urban density, and area and two main environmental variables of elevation and regional climate have a degree of association with the physical growth patterns. However, there is a need for more detailed data and variables for explanation of the physical patterns of Iranian cities.