عنوان مقاله [English]
Identification, Evaluation and the Management of Dust Sources in Western Iran
Dust storms are atmospheric events caused by the removal of fine particles from the surface of the earth. Not only natural but also human factors are involved in the emergence of dust. As human activities change the stability of geomorphic surfaces, areas susceptible to wind erosion may increase and the release of waste materials will increase abruptly. Dust can have devastating effects on the environment and human activities, which has many consequences for human society. Researches show that in Iran, the phenomenon of dust, especially in western provinces such as Kermanshah, is so widespread that researchers regard it as the most important environmental problem. The dust that affects the western and southwestern parts of the country is mostly trans-local and originates from neighboring countries. But in recent years, with increasing environmental changes in the country's western provinces, attention has been drawn to the potential production of domestic dust sources. A new pathway to environmental management and control measures will be opened if the dust sources are identified. Therefore, in this study, in addition to identifying the origin of dust and its prone areas in Kermanshah and Ilam provinces, it is attempted to study the characteristics of these areas in terms of land cover and geomorphology. Attempts have been made to identify the factors that have caused and exacerbated this phenomenon in recent years to prevent and reduce the occurrence of this phenomenon given the environmental conditions and facilities available.
Methods and Materials
In this study, meteorological data were used to determine the occurrence of dusty days and satellite images were utilized to identify dust sources. Days were considered as days of dust occurrence where at least one station had recorded meteorological codes related to the dust phenomenon and had a horizontal visibility of less than 1000 meters. Out of 210 days of dust, 21 images (from 2008 to 2008) were selected to identify the origin of dust and the rest were excluded for various reasons. In order to detect dust, first, MODIS images were geometrically corrected in the ENVI 5.3 software. Then, using software Erdas Imagine 9.1 and TDI Index the dust was detected. In this study, in addition to satellite imagery, Hybrid Single-Particle Lagrangian Integrated Trajectory )HYSPLIT( was also used to identify the direction of wind movement and the origin of dust. After making radiometric and atmospheric corrections, four land use classes were extracted (forest, rangeland, agriculture, and built-up land) in 2000 and 2015 with Maximum Likelihood algorithm in Software ENVI 5.3.Finally, by comparing these two maps, land use change map was prepared and seven land use changes classes (forest to rangeland, forest to agriculture, rangeland to agriculture, forests to built-up land, rangeland to built-up land and agriculture to built-up) land were extracted in total. To prepare the geomorphological map, the geomorphic classification scheme of Boulard et al. (2011) was used. For this purpose a combination of remote sensing and Landsat imagery data, 1: 100,000 geological maps of Iranian oil operating companies, the Iranian geological survey and mines exploration resources and land capability map (The soil texture profile of the area was extracted from this map) were used. After determining the geomorphic unit boundaries of each polygon, it was assigned to one of the 17 geomorphic classes classified by Boulard et al. (2011). Finally, the origin of the identified dust points was overlaid on these maps and their distribution and frequency were determined for each geomorphic class and land use change.
Results and discussion
This study identified dust sources in Kermanshah and Ilam provinces and examined the role of land use change and geomorphology with regard to dust production. A total of 396 dust sources were identified during the study period (years 2008-2013). On each image, the number of sources identified varied from 2 to 15 points. The dispersion of the dust sources detected on 21 satellite images shows that Kermanshah and Ilam provinces do not produce the same amount of dust, but most of the dust sources originate from several important areas in the west of these provinces including areas around Ezgeleh, Qasr-e Shirin, Naftshahr, Sumar, Mehran, Dehloran and Abu Ghovair village. Evaluation of the characteristics of dust sources shows that areas affected by land use change have the most potential for dust generation and among different classes of land use change, land use change from rangeland to agriculture has had the highest effect in dust production. In addition, Of the 17 geomorphic classes identified by Boulard et al. (2009), there are 6 classes in Kermanshah and Ilam province. Geomorphologically, alluvial systems are the most important producers of dust and among the different types of geomorphology, the class 2C has a more significant role in the production of dust. The dusts identified on the MODIS images show that a large number of these are originated from piedmonts and alluvial fans near the Zagros Mountains (class 2C). In addition to piedmonts and alluvial fans, alluvial plains and floodplains (3c, 3d) are other important geomorphological species in the region that have contributed significantly to the production of dust. In the seven important dust producing regions identified in Kermanshah and Ilam, different land use and geomorphology classes do not produce the same dust, so the most appropriate method for combating wind erosion should be selected in each region.
Evaluation of the severity of wind erosion in the dust producing areas of Kermanshah and Ilam indicates that anti-erosion methods should be prioritized in piedmonts, alluvial fans, alluvial plains and floodplains. Some measures should be taken to prevent wind erosion at the source and others should be outside the source and upstream (watershed measures).In natural ecosystems and rangelands, it is best to avoid change of use, over-grazing, etc.to prevent wind erosion. In agriculture controlling measures that make the soil less vulnerable to wind, such as crop residues, gravel mulch should be taken. Pebbles or gravels should be used to restore natural vegetation in grasslands that have become arable land.