تخمين نرخ تغييرات پهنه‌هاي فرسايش بادي مبتني بر مدل IRIFR و مدل استخراج كاربري اراضي و پوشش زمين از تصاوير ماهواره لندست (منطقه مورد مطالعه: دهستان ماژان، استان خراسان جنوبي)

Estimation of Variation Rate of Wind Erosion Zones Based on the IRIFR Model and Land Use and Landcover Extraction Model by Using Landsat Satellite Images (Case Study: Mazhan District, South Khorasan Province)

حدود 24 درصد از اراضي قابل سكونت زمين تحت تأثير فعاليت‌هاي انساني است كه كاهش حاصل خيزي خاك را به دنبال دارند. يكي از مهم‌ترين اثرات فرسايش بادي، از بين رفتن تنوعات زيستي و از بين رفتن ظرفيت توليد زمين تحت عنوان بيابان‌زايي است. بيابان‌زايي به‌طور دائم و البته نه انحصاري در مناطق خشك اتفاق مي‌افتد. دهستان ماژان شهرستان بيرجند با كاربري كشاورزي و دامداري از جمله مناطق تحت تأثير فعاليت شديد فرسايش بادي در استان خراسان جنوبي است. متوسط بارندگي سالانه در اين دهستان طي يك دوره 20 ساله برابر با 154 ميلي‌متر بوده و به‌ طور كلي اقليم آن از نوع خشك و بياباني است. هدف از اين مطالعه، تخمين نرخ تغييرات پهنه‌هاي فرسايش بادي طي دوره زماني مشخص با استفاده از تصاير ماهواره لندست است. براي مطالعات فرسايش باد از مدل‌هاي فرسايش با اهداف مختلف شامل: تخمين متوالي فرسايش و طراحي ابزارهاي كنترل فرسايش، استفاده مي‌شود. موضوع مهم در مدل‌سازي فرسايش باد، ارائه تعريفي واضح جهت تشخيص موضوع و نيز بررسي داده‌هاي موردنياز و موجود براي اجراي مدل است. در اين مقاله اطلاعات حاصل از دو مدل شامل: مدل پهنه‌بندي فرسايش باد IRIFR و مدل استخراج طبقات كاربري اراضي و پوشش زمين از تصاوير ماهواره‌اي، تلفيق‌شده است. در نهايت به كمك روش آماري چند متغيره، تغييرات زماني و مكاني پهنه‌هاي فرسايش باد موردبررسي قرارگرفته است. نتايج نشانگر وقوع بيشترين نرخ تغييرات در پهنه‌هاي فرسايش بادي با شدت متوسط بر روي لند فرم‌هاي مخروط افكنه است. همچنين اولين مؤلفه اصلي كه دربردارنده 98/89 درصد تغييرات پهنه‌هاي فرسايش بادي است، بهترين نماينده وضعيت تغييرات در پهنه‌هاي فرسايش بادي طي دوره مورد بررسي است.

Introduction The estimated surface area affected by human-induced soil degradation is 24% of the inhabited land areas. A major impact of desertification is loss of biodiversity and loss of capacity of land which is known as desertification. Desertification permanently, but not exclusively occurs in arid regions. Mazhan district of Birjand city bears agriculture and livestock activities, including areas affected by severe wind erosion in the South Khorasan province. Average annual rainfall in the district during a 20 year period is equal to 154 mm and are generally dry and desert climate. The aim of this study was to investigate the variability of wind erosion zones specified period using Landsat satellite images. Material and Methods The study area is located in the south of Birjand, South Khorasan province. It is an area of 758.1 square kilometers and consists of the most villages in the southeastern city of Khoosf. Topography of the area classified in four units: plain in the center (central Kavir), pediment of south mountains, hills and mountains along the NorthWest to South-East. Pediments are the main geomorphological landforms. Wind erosion models are used for a variety of purposes including estimating consequences of wind erosion, as well as for designing erosion control measures. In this paper, the wind erosion IRIFR zoning model and land use and land cover classes model that derived from satellite imagery has been used. Temporal and spatial variations of wind erosion zones with the help of multivariate statistical methods have been studied. IRIFR model for wind erosion zoning is the most commonly used model that is based on environmental conditions and climate of our country and several studies with different application purposes and designs, using this model have been. In this model 9 factor according heavily in wind erosion and weakness of each factor and its impact on the sedimentation, evaluating and scoring are based on geomorphic units. Summation of these factors per unit of geomorphology is evaluating the severity of wind erosion over the years. Land use and cover, is important as a key variable in the IRIFR model, while the model result show a stable condition during different times. For this purpose, according to the Landsat satellite images to calculate soil erosion, 6 periods of Landsat satellite images for mapping land cover has been used for different time period. Hence, early map of wind erosion of the modeiiRIFR converted o the multiple maps at different times in throughput that shows each spatial variation of intensity of wind erosion according to satellite images taken. Change of wind erosion rate with subtraction of hazard maps of wind erosion at different times and calculate the average rate of change has been made. Principal component analysis (PCA) also taking into account the spatial and temporal changes in intensity of wind erosion at different times, a map containing most of the changes in wind erosion zones investigated during the period as a result of this. Discussion Average accuracy of land use and land cover classification from 6 period satellite images is 79 percent with 0.83 kappa coefficient. Most of the changes happened in the areas of cultivated land in the region. Spatial variations in wind erosion areas during the 6 period show the most change in the middle class. This class is actually alluvial fan landforms that play important roles in the production of wind deposits are included. The process of transformation in the classes shows that reducing the effectiveness of the landforms and consequently a significant reduction in the intensity of wind erosion in the study area. Examination of changes significantly over time using a spatial correlation maps matrix calculation is performed. The results indicate no significant correlation between wind erosion zones in longer time intervals (for example, the years 1387 and 1389 with earlier periods) and there was significant correlation between zones in shorter intervals. Conclusion The results indicate the highest rate of occurrence of wind erosion in areas of moderate intensity on the geomorphologically alluvial fans. The first principal component, which contains 98.89% of the variation in the areas of wind erosion, is the best representative of the area during the period under consideration.