چكيده لاتين :
Currently, desertification phenomenon is being spread throughout the world including Iran. This problem not only imposes the arid and semi-arid regions but also affects semi-humid regions. Desertification event is induced by both natural factor and improper anthropogenic activities. Therefore, combating desertification needs modeling the effective factors and characteristics. This study aims at evaluating desertification hazard using Iranian Model of Desertification Potential Assessment (IMDPA) model which is adapted to the holistic model. This research is conducted at Gandomban plain, Ghasr-e-Shirin, Iran. However, quantities evaluation of desertification hazard is carried out based on three main factors including climate, water, and geomorphology. The factors comprise 11 indices. Each index estimated, mapped and prioritized based on its weighted mean using Arc GIS software. The result explored that the study area can be classified into three classes including low (5.38%), moderate (72.53%) and high (22.08%) indicating moderate class for the study area. The effect of climate on desertification was found moderate, while water and geomorphology factors share severe development of desertification event. By and large, the prioritized indices were found deficit of groundwater, geological formation and electrical conductivity (EC), respectively. In contrast, sodium absorption ratio (SAR) and chloride were lower and neutral agents. It is concluded that the study area is suffering from desertification hazard inducing the shortcoming of groundwater phenomenon.
Keywords: Desertification Criteria, Desertification Indices, IMDPA Model, Gandomban Plain, Iran
Extended Abstract
1-Introduction
Nowadays, desertification, as a problem, affects many countries, including developing countries. This problem is presented not only in arid and semi-arid areas but also in parts of semi-humid too. Despite the definitions with the same contents about desert and desertification in the world, a specific and unique method for classification of deserts and desertification rate estimation have not been presented yet. Perhaps the main reason for this difference is that the indices on environmental conditions and social and economic structures of various desert regions in the world are variable. The best way to determine the criteria or factors affecting desertification, in general, is regional and local models in the form of specific criteria and indicators of that area.
2- Materials and Methods
Gandomban plain is a part of Qasr-e-Shirin city in the Kermanshah province with about 11445 hectares area which is the neighbor of Iraq from North and West, from the south to the suburb of Qasr-e-Shirin located in the East of Dasht-e-Zahab village. IMDPA method is used in order to evaluate the potential desertification in the study area. According to this method, the intensity of desertification is evaluated by using three criteria: climate, water and geology and geomorphology as key criteria desertification. The geometric mean of annual rainfall, drought and the continuing drought indices are calculated as the climate criterion, the geometric mean of Electrical Conductivity (EC), Sodium Absorption Ratio (SAR), soluble solids in water, chlorine and fluctuations in groundwater level indices as water criterion and geometric mean of slope, formation erodibility and land use indices as geology and geomorphology criterion. Finally, using geometric mean of criteria, the potential final map of desertification was extracted.
3- Results and Discussion
To determine the numerical value of the desertification intensity, and relevant degree, 4 desertification classes of low, moderate, severe and very severe selected based on the model and for each index a map was prepared according to the weighting method. Also for climate, water, geology and geomorphology criterion, relevant maps were drawn. Based on IMDPA model, desertification intensity map of Gandomban plain was obtained by overlapping information layers of climate, water, geology and geomorphology criteria and the potential desertification map of study area extracted. The intensity of desertification in the study area was classified into three classes: low (5.38%), moderate (72.53%) and severe (22.08%). Assessing the numerical value of indices showed that the groundwater depletion is the most effective factor in the severity of desertification in the study area. The weighted average potential desertification in the study area was 72.53%, which is placed in the moderate class of desertification.
Evaluation and comparison of the criteria results showed that the intensity of desertification of climate criterion is in the moderate class. Besides, the intensity of desertification of water and geology and geomorphology criteria was classified as a severe class. Based on the results, the most important indices of desertification in Gandomban plain are decline of water level, formation sensitivity to erosion, and Electrical Conductivity (EC) in order.
Soil stability of the region is severely damaged because of destroying the natural vegetation cover and lead to flooding and soil salinity of fields. On the other hand due to the high-level clay and silt in the soil of study area dust storm will become a problem in future. Another important reason of desertification is the excessive use of groundwater and drilling of numerous wells due to agricultural expansion and the use of traditional irrigation systems, which in recent years has led to a sharp depletion in the water table in the area reflecting as the main criterion of desertification in this study.
4-Conclusion
According to the analysis and the results of the evaluation method used in Gandomban plain, IMPDA model with consideration of appropriate and relatively sufficient indicators in dry areas and due to simplicity and step-by-step ways, specific indices weighting method and using the geometric mean rather than sum or arithmetic mean in calculating the indices and also use of GIS in overlaying method for obtaining the final map of desertification is fairly accurate and can be used in similar areas to determine the extent of desertification, also if necessary the indicators can be modify based on the study area condition.
