تعیین ویژگی های ژئومورفولوژی و کاربری اراضی کانون های برداشت گردوغبار (مطالعه ی موردی: خراسان رضوی) (مقاله علمی وزارت علوم)
درجه علمی: نشریه علمی (وزارت علوم)
آرشیو
چکیده
یکی از مهم ترین مخاطرات در نواحی با اقلیم خشک و نیمه خشک، پدیده ی گردوغبار است. وقوع این پدیده با خسارات جانی و مالی و طبیعی بسیاری همراه است. در این تحقیق به بررسی خصوصیات کاربری اراضی و ژئومورفولوژی کانون های برداشت گردوغبار در استان خراسان رضوی پرداخته شد. در ابتدا با استفاده از شاخص های آشکارسازی گردوغبار بر روی تصاویر ماهواره ای مادیس، تعداد 65 کانون برداشت گردوغبار برای دوره ی آماری (2016-2005) شناسایی گردید. سپس نقشه ی واحدهای ژئومورفولوژی و کاربری اراضی منطقه تهیه گردید و کانون های برداشت گردوغبار بر روی این نقشه ها هم پوشانی داده شد. نتایج حاکی از آن است که از لحاظ ژئومورفولوژی 81 درصد کانون های گردوغبار در واحد دشت سر مشاهده شده است که حدود 5/71 درصد مساحت منطقه را دربر می گیرد. در دیگر چشم اندازهای ژئومورفولوژی، کانون های گردوغبار به ترتیب در واحد پلایا (7/ 10% در 5/17% مساحت) و کوهستان (6/4% در 14% مساحت) قرار گرفته اند. نتایج حاصل از بررسی کاربری اراضی نشان داد که بیش ترین تعداد کانون های برداشت گردوغبار در کاربری مراتع ضعیف (3/35%) و اراضی دیم (6/27%) رخ داده که حدود 3/35 درصد مساحت از کل منطقه را دربر گرفته اند. با محاسبه ی نرخ گردوغبار در سطوح مختلف مشخص شد که علاوه بر نوع ساختار ژئومورفولوژی و کاربری اراضی، ارتباط تنگاتنگی بین مساحت و تعداد کانون های برداشت گردوغبار هر واحد با نرخ انتشار گردوغبار وجود دارد.Determination of Geomorphological and Land Use Features of Dust Harvesting Sources (Case Study: Khorasan Razavi Provience)
Introduction
Dust phenomenon is the One of the most important hazards in the dry and semi-arid region. The occurrence of this phenomenon is accompanied by many physical and financial losses. Iran is exposed to numerous local and trans-regional dust systems due to being in the arid and semi-arid belt of the world. Observations of recent years indicate an increase of this phenomenon in the country. Surface properties of dust harvesting zones affect the amount, intensity, and type of dust particles entering the atmosphere. Consequently, it is important to know the geomorphological and land use characteristics of the dust harvesting areas. Land use changes associated with global climate change have a significant relationship with desertification and increasing dust storms. Changes in river floods and the level of temporary and permanent lakes in dry and semi-arid environments cause significant fluctuations in the amount of dust in these areas. The purpose of this research is to determine the role of each geomorphological feature and land use in dust source regions in Khorasan Razavi province.
Materials and Methods
In this study, land use and geomorphological characteristics of dust harvesting zones in Khorasan Razavi province were investigated. At first, 65 soil dust sources were identified for the time period (2005-2016) by using the dust detection indices on the MODIS images. After preparing the distribution map of dust collection centers in GIS environment, land use maps and geomorphology of the region were prepared to determine the role of each of the geomorphological and land use features of the studied area in the emission and occurrence of dust. By comparing both geomorphological and land use maps with the identified dust harvesting centers, the number of sources of dust for each geomorphic map and land use were determined. In this study, we present the ratio of dust emissions as a unit of relative dust production measurement for each class. This ratio was calculated by dividing the percentage of total dust harvesting centers in each geomorphic group or land use by the percentage of the total area occupied by this class.
Discussion and Results
Using four methods of false color combination and applying them to existing images, the dust and dust masses were detected on the images and then, by their visual interpretation based on Gaussian Plum emission model, the dust starting point was determined. A total of 65 dust harvesting points were identified in the studied area. In order to prepare a geomorphologic map, a slope map was first developed, because one of the variables that plays a crucial role in the separation of geomorphological units is the slope map. In this research, a slope map was made using a 30-meter DEM, and according to this, the studied area was geomorphologically divided into 3 units of mountain, pediment plain and Playa plains. Thus, the slope is 0-1%, Playa unit, 20-20%, pediment plain unit and slopes greater than 20%, Mountain unit. In order to prepare the land use map, after providing false color images (bands 4, 2, 2), of Landsat ETM + (8) satellite data from 2016, with the help of educational samples and using the classification method, the land use map of the studied area was prepared.
Most of the land uses are rangelands (rich, medium and poor) covering about 60% of the area. Most of the dust centers occurred related to the poor pasture usage, which are usually prone to dust due to lack of vegetation. In terms of the rate of dust emission, the most emission rate is related to clay surfaces that cover a small area of the area, which indicates the relationship of the area with the emission rate of dust. Geomorphological map includes 3 units (mountain, pediment plain and Playa plains). The pediment plain cover a wide range of arid regions, and in this research most of the area (71.5%) is related to this unit. The highest number of dust source sites and dust emission rates occurred in the pediment plain, Playa plains, and mountains, respectively, indicating that the plains are susceptible to the occurrence of dust in the studied area.
The results indicate that 81 percent of the dust source area were observed in pediment plain area geomorphologically, covering about 71.5 percent of the area. In other geomorphological landscapes, dust centers are located in the Playa unit (10.7% in 17.5% of the area) and in the mountains (6.4% in 14% of the area) respectively. The results of land use survey showed that the most number of dust harvesting centers occurred in poor rangelands (35.3%) and dryland lands (27.6%), which covers 35.3% of the total area.
Conclusions
By calculating the dust rate at different levels, it was determined that in addition to the type of geomorphology and land use structure, there is a close correlation between the area and the number of dust harvesting centers per unit with the emission rate of dust.
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