پديد آورندگان :
زهتابيان، غلامرضا دانشگاه تهران - دانشكده ي منابع طبيعي - گروه احياي مناطق خشك و كوهستاني , خسروي، حسن دانشگاه تهران - دانشكده ي منابع طبيعي - گروه احياي مناطق خشك و كوهستاني , اسكندريدامنه، حامد دانشگاه تهران , ابوالحسني، اعظم دانشگاه تهران - دانشكده ي منابع طبيعي
كليدواژه :
اطلس بيابانزايي , مدل IMDPA , معيارها و شاخص‌ها , ايران , اطلس بيابانزايي
چكيده لاتين :
Desertification means land degradation in the arid, semi-arid and dry sub-humid regions because of natural or anthropogenic factors. Desertification is accounted as the third most important global challenge after the crisis of water shortage and drought in the 21st century. Desertification is a problem for many countries, especially the developing countries. Identifying the regions exposed to desertification is so important for combating desertification and leads to better planning. Also the awareness of inappropriate management practices can reduce the intensity of this phenomenon, and prevent its development. There are many models for preparing desertification maps in the world that the most common of which includes UNEP-FAO, ASSOD, GLASSOD, LADA, and MEDALUS. Also in Iran ICD, MICD and recently, IMDPA models have been presented. IMDPA model includes some criteria affecting desertification, and some indicators for the quantitative assessment of the criteria. In this research IMDPA model was used for the assessment of Iranian desertification condition.
2-Methodology
IMDPA model have 8 criteria which are called desertification criteria and their indicators are used for quantifying them. At first 130 indicators were selected for all 9 criteria but on the one hand it wasn’t possible to prepare information of all of them for the whole of country and on the other hand it was costly and time consuming. So for each criterion, up to 4 key indicators were identified. Indicators related to each criterion are as follows:
Climate: drought, aridity index, rainfall amount.
Geomorphology: land use, rock sensitivity and physiography.
Water: negative balance of water, groundwater depletion, EC and SAR.
Soil: EC, texture, depth, gravel percentage.
Vegetation cover: coverage status, coverage utilization and vegetation cover rehabilitation.
Erosion: water erosion (vegetation cover density, land use and water erosion density and type) and wind erosion (days with dust storm index, vegetation cover, non-living cover density and erosion faces appearance).
Socio-economic: socio-cultural factors, organization and participation, awareness, experience and native knowledge. Urban or technology development: mine and road density, converting forests and rangelands to urban and industrial areas, improper agriculture, converting garden lands to residential-industrial regions and amount of green space per person.In this study each index received a weight (1 to 4) according to expert opinions and each criterion was obtained based on its indicators’ geometric mean according to the formula below:Index X: each criterion
Layer: indicators related to each criterion
N: number of indicators related to each criterion
Weighted averages of indicators related to each criterion were determined and finally desertification intensity was gained based on the geometric mean of all criteria according to the formula below:
Then, final map of desertification intensity was determined using different layers and obtained maps related to each criterion and combination of layers and maps. So, the map of each criterion status was obtained from its own indicators. These maps can be used for the study of each index quality and its effect on desertification.
3- Results
3-1-Map of water and irrigation criterion
The result of the quantitative value of this criterion that was determined using its indicators is shown in Figure (2). The zoning map of Iran plains based on Q3 is shown in Figure (3). Also this calculation result is shown in Table (2).
3-2-Map of vegetation cover criterion
The map of Iran’s desertification condition based on vegetation cover or Q5 is shown in Figure (4). Table (3) shows all of its information. Also the zoning map of Iran’s plains based on Q5 is shown in Figure (5).
3-3-Status quo of Iran’s desertification
Finally, the intensity map of Iran’s desertification was prepared and the calculation was done in order to determine the classes of desertification (Table 4).
4-Discussion and conclusion
In this research IMDPA model was used in order to prepare Atlas of Iran’s desertification. In this model, there are 8 criteria which are regarded as desertification criteria and their indicators are used for quantifying them. At first, 130 indicators were selected for all the 9 criteria but on the one hand it wasn’t possible to prepare the information of all of them for the entire country, and on the other hand, it was costly and time consuming. So for each criterion, up to 4 key indicators were identified. The desertification intensity map of Iran was determined using these criteria and indices, and also, they were quantified in the arid, semi-arid and sub-humid regions.
The results showed that 88.73% of the country surface was affected by desertification which is equal to 143365238.6 hectares. The surface of more than 49425703.3 hectares equal to 30.59% of the total surface of the country was in the low desertification class, the surface of more than 935677913.6 hectares equal to 57.91% was in class II or medium, and a surface about 371621.7 hectares equal to 0.23% was in class III or intense. Class IV of the desertification or very intense was omitted regarding to IMDPA model and the 8 criteria, and the natural desert areas whose surface was equal to 15624274.3 hectares or 9.67% were beyond this class.
