عنوان مقاله [English]
Irregular increasing of population and increasingly needs to food and new resources of energy have been caused unprincipled impermanent utilization of natural resources. A phenomenon their bad conclusion in dry and semi-dry ecosystems is more widespread and irreparable due to its sensitivity and vulnerability. A method to evaluate desertification potential risk has been prepared by FAO/UNEP which considered the natural factors and human activities such as population pressure and grazing intensity. Hence, in this study the desertification severity was determined by the FAO/UNEP method, in addition to population variations from 1956 to 2006 in Kashan basin which is one of the sub basins of salt lake of center of Iran.
Population centers are located in the south, west and northwest of the studied basin and rest of the basin is out of population according to the dry and desert conditions. This population distribution with variations and fluctuations has been caused excess density out of environment capacity in some regions, especially urban areas. So the alterations of Kashan population in 1986, 1966, 1976, 1986, 1996 and 2006 has been alternated 45955, 58468, 84863, 138599, 201372 and 253509 respectively which shows 4000 people increasing per year (Statistical center of Iran). In order to monitor these variations and their effects on environment, indicator of potential status ratio, was used as one of the effective factor for determining desertification rate. Intensity amount is shown in table 1. Ratios less than 1 in any region reflect strong and very strong desertification. According to the reported data from Statistical center of Iran, current potential status of population can be obtained and then can be used to determine the ratio. However, in order to estimate the potential adoption capacity of population, several ways are provided. The newest method in this field was done by USDA (1999) which was used in this study. In this method, depending on the quality of soil and effects of climate, different function levels have been identified for lands. In first stage, by combining properties of soil, climate, temperature and moisture regime and reconstruction ability of the soil, nine quality classes are obtained, which actually indicate the natural quality of the lands. Accordingly, class 9 is the poorest and class1 is the best class in terms of quality. Desired population adoption capacity for each class of quality, which determined in pervious stage, is shown in table 2. Amounts table 2 has been obtained empirically or in experiences. Provided population capacity for each class of land quality in this table is the best current estimation which based on per capita income of individuals and some level, in a way that per capita income less than 1000 dollars indicates low level of sources, from 1000 to 7000 dollars indicates medium level and more than 10000 dollars indicates high level of sources. Regarding to source level and land quality class, potential adoption capacity of population is estimated according to the number of people per hectare. Finally, by the obtained proportion from potential and actual capacities, pressure of human population was estimated and categorized in table 1.
Table 1: Investigation of population pressure on environment
Studies on this research shows this fact that during the last 50 years, increasing in population in special regions, mainly in cities, have decreased about 7 % of the area of the regions with a slightly desertification and increased the area of regions with a strong desertification (table 3)
Table 3: Area of desertification various degrees
Towns Kashan, Aran & Bidgol, Meshkat, Sensen, Abshirin with a slightly desertification in 1986 have converted to strong desertification regions, which obviously show the immigration rate from villages to the city and its bad effects.
Study of data showed that population pressure, especially in city regions is increasing. One of its main reasons is immigration of villagers to the cities for more earnings. Of the guidelines to cope with increasingly pressure of population on the environment in this area, is to increase amount of source through raising productivity and more earnings. Agriculture is as the main basis for production in the region and its efficiency can be increased by water management. Change of irrigation from submerged to under pressured method, change of crops cultivation from high water need (especially vegetables) to crops with middle to low water need, feeding of ground water table through different ways of aquifer holding and using crop rich varieties are of the water management methods in this area. Proper distribution of well-being, health care, and educational facilities are the other effective guidelines to prevent excess immigrations to the cities.