بررسي ابعاد جغرافيايي و پتانسيل توليد اراضي كشاورزي تغيير كاربري يافته در اثر توسعه بي برنامه كلان شهرهاي ايران

Assessing geographical distribution and potentialities of agricultural lands, destructed by residential sprawl on the fringes of big cities of Iran

At the present time, the improper land use change in the fringes of big cities and smaller urban areas of Iran has turned to a big challenge, which puts agricultural production at risk. This research was conducted in the framework of a research project sponsored by Soil and Water Research Institute of Iran. The aim was to acquire quantitative data on geographical distribution, potentialities and production capacity of soils of agricultural lands that were converted to urban uses on the fringes of six big cities of Iran, namely Tehran, Karaj, Tabriz, Ahwaz, Shiraz and Mashhad cities and their suburbs. The geographic extent of urban areas in 1955 was delimited on a photo-interpretation map which was produced by interpretation of air photos, obtained in the same year. Similarly, the limits of residential sprawl into agricultural areas between 1955 and 2001 were determined on a map that was produced by visual interpretation of satellite image of 2001. The information on geographical distribution and potentialities of soil resources were extracted from soil maps, produced by Soil and Water Research Institute of Iran. In areas where soil maps were not available, land class and soil production capacity were estimated based on knowledge of soil survey experts. Separate information layers, produced in this research, were integrated in the ARC/INFO environment. Data integration led to information extraction on the aerial extent of urban sprawl and the lost opportunities for agricultural production on the converted farmlands. The results are indicative of rapid conversion of agricultural lands to urban areas over the past five decades. Between 1955 and 2001, more than 2,950 hectares (ha) of agricultural lands per year were converted to urban uses on the fringes of the six big cities of Iran and their suburbs. Population of these cities increased seven fold (except for Karaj city with a population increase of about 75 times), while their population density decreased about 67%, leading to an increase of more than 260% in per capita land in urban areas, during the same period. More breathing space for residents of urban areas was achieved to the price of lack of ability to produce 500,000 tons of wheat that could be produced a year,on 136,000 ha lost farmlands, including 39,000 ha class-I land with soils having no limitation, 43,000 ha class-II land with slight limitations, and 54,000 ha class-Ill land with soils having moderate limitations for Irrigated agriculture.