اولویت‌بندی مناطق حساس به فرسایش خاک با استفاده از تصاویر ماهواره ای (مطالعه موردی: بخشی از شهرستان بهمئی در استان کهگیلویه و بویراحمد)

تاکنون اقدامات و فعالیت های گوناگونی برای کاهش و جلوگیری از اثرات مستقیم و غیرمستقیم فرسایش خاک صورت گرفته است اما به دلیل منابع مالی و انسانی محدود غالباً نمی توان این فعالیت ها را در کل یک منطقه حساس به فرسایش اجرا کرد؛ بنابراین شناسایی مناطقی که نیازمند توجه ویژه برای اجرای اقدامات حفاظت خاک هستند، ضروری به نظر می رسد. این تحقیق با هدف ارزیابی خطر فرسایش‌ خاک و توزیع مکانی آن با استفاده از مهم‌ترین عوامل موثر بر فرسایش خاک و شناسایی و اولویت بندی مناطق حساس، به منظور انجام طرح‌های حفاظتی کوتاه‌مدت و بلندمدت در پهنه جنوبی شهرستان بهمئی غالباً متشکل از سازندهای فرسایش پذیر گروه فارس واقع در جنوب غربی استان کهگیلویه بویراحمد صورت گرفته است و برای تحقق این هدف، تصاویر سنجنده های etm+ و oli ماهواره لندست در سال های 2003 و 2017 به کار گرفته شد. خطر فرسایش خاک بر اساس یک متدلوژی کیفی و عکس العمل بین شیب زمین، پوشش گیاهی و کاربری اراضی ارزیابی و با توجه به استاندارد تخصصی sl 1902007، در شش کلاس خیلی کم، کم، متوسط، شدید، خیلی شدید و فوق العاده شدید طبقه‌بندی و رتبه‌بندی شد. در تحلیل جداگانه ی پارامترهای مورد بررسی، نتایج نشان داد که حدود 80 درصد منطقه مورد مطالعه دارای شیبی کمتر از 30 درصد بوده که از این نظر منطقه باید فرسایش خاک کمی داشته باشد. مطالعه ی وضعیت پوشش گیاهی در دوره زمانی مورد بررسی نشان داد که در سال 2003، حدود 8 درصد از منطقه، دارای پوشش گیاهی بیشتر از 60 درصد است، در صورتی که در سال 2017 این میزان پوشش گیاهی فقط حدود 0.2 درصد از منطقه را به خود اختصاص داده است. این کاهش پوشش گیاهی به مرور زمان می تواند منجر به افزایش خطر فرسایش خاک شود. در بررسی تغییرات کاربری اراضی نیز مشخص شد که کاربری کشاورزی و مسکونی به میزان 37 درصد افزایش پیدا کرده است به نظر می رسد، تغییرات کاربری می تواند منجر به افزایش فرسایش خاک در منطقه گردد. نتایج تحلیل اثر متقابل پارامترهای مورد مطالعه در تهیه نقشه خطر فرسایش در منطقه حاکی از این است که میزان پهنه های خطر فرسایش متوسط تا فوق العاده شدید در بازه زمانی تعیین شده، حدود 20 درصد افزایش پیدا کرده است. در مطالعات فرسایش خاک، از طریق تجزیه و تحلیل اثر متقابل عوامل اثرگذار به‌صورت کیفی می توان خطرفرسایش را تعیین و احتمال نسبی وقوع فرسایش در یک محل در مقایسه با سایر محلات را تخمین زد. نتایج این تحقیق می تواند مبنایی برای اولویت بندی اجرای فعالیت های حفاظت خاک و تخصیص اعتبارات و مدیریت سرزمین توسط سازمان های دولتی در پهنه جنوبی شهرستان بهمئی باشد.

Prioritization of erosion-sensitive areas using satellite imagery (Case study: part of Bahmei county in Kohgiluyeh and Boyerahmad province)

Extended abstract1 IntroductionVarious measures and activities have been taken to reduce and prevent the direct and indirect effects of soil erosion but due to limited human and financial resources, it is often not possible to carry out these activities in a whole erosionsensitive area; therefore, identification of areas requiring special attention to conservation is essential. Without prioritizing the watershed, many financial resources will be wasted, so mapping, monitoring, and prioritizing areas for erosion control will be required to avoid wasting funds. Therefore, prioritizing conservation areas at risk of soil erosion is an important consideration in natural resource management planning that allows decision makers to implement management strategies that are more sustainable in the long term. A review of the research background showed that almost no quantitative field measurements of soil erosion were performed using standard protocols in southern part of Bahmaei County. Also, no study has been conducted in Bahmaei County that has analyzed the spatial trends of erosion and its relationship with the effective factors. There is no information about erosion patterns and its dynamics in Bahmaei County in any study. Therefore, this study uses a relatively simple qualitative method by analyzing the interaction of three indicators of slope, vegetation and land use with the aim of helping to fill the existing gap for mapping and prioritizing lands in the southern part of Bahmaei County based on their sensitivity.2 MethodologyThe study area is southern part of Bahmaei County in Kohgiluyeh and Boyerahmad province with an area of about 40306 hectares and an average elevation of 623 meters above sea level. The average rainfall in this region is about 400 mm. About 60% of Southern part of Bahmaei County is composed of erosionsensitive formations of Gachsaran, Mishan and Aghajari consisting of clay, marl and gypsum, which is also in a very weak condition in terms of vegetation. However, developing soil erosion management strategies in this area is very limited due to lack of data. The rate and amount of soil erosion is influenced by topographic factors, vegetation, rainfall and runoff, soil erodibility, and land cover (Wang et al., 2013). The intensity, duration and frequency of rainfall are important factors in soil loss that are affected by climate, while vegetation and slope are factors that determine soil resistance to erosion. In this study the risk of soil erosion was evaluated on the basis of the reaction between the slope angle, vegetation cover and land use and, according to the SL 1902007 standard, classified and ranked in very low, moderate, severe, very severe and highly inflated classes.3 Results Investigation of the parameters affecting soil erosion showed that slope class 0 to 5 ° had the highest percentage of area (40%) and slope class greater than 35 ° had the lowest area percentage (1%) in the study area. This is indicative of the low slope and lowland area and the area should have little soil erosion. In 2003, class 45 to 60% had the highest amount (92%) and class less than 30% had the lowest amount (0.0007%) of vegetation, and in 2017, class 30 to 45% had the highest amount (81.6%) and class more than 75% have the lowest amount (0.065%) of vegetation. This indicates a decrease in vegetation over time in the study area. Land use maps prepared from the study area show that the percentage of rangeland, farmland, garden and residential land uses in 2003 were 84.7%, 12.6%, 0.8% and 1.8%, respectively, and in 2017 it was reached 44.6, 49.5, 3.2 and 2.5%. In other words, in the last 14 years (2003 to 2017), about 16143.5 hectares of rangelands area has been reduced, 14863.9 hectares have been added to farmland, 972.5 hectares to gardens and 307.1 hectares to residential use. In 2003, rangeland use had the highest percentage of area (84.7%) and garden use the lowest percentage of area (0.8%) and in 2017, farmland use had the highest percentage of area (49.5%) and residential use had the lowest percentage of area (2.5%) in the study area, which indicates a significant increase in agricultural growth, including agriculture and horticulture in the study area in recent years. The results showed that in 2003, the very low erosion risk class had the highest percentage of area (41%) and the risk of extreme erosion, the lowest percentage of area (12.2%), and in 2017, the very low erosion risk class has the highest percentage of area (40%) and the risk of extreme erosion class, the lowest percentage of area (29.2%) in the study area. In the study of changes in the erosion zones in the study period in the study area, it was determined that the very low and low erosion class from 2003 to 2017 has been decreasing trend and the rest of the classes have been increasing trend, which indicates an increase in the amount of erosion in the study area. 4 Discussion ConclusionsIn a separate analysis of the studied parameters, the results showed that about 80% of the study area has a slope of less than 30%, in this regard, the area should have little soil erosion. The study of vegetation in the study period showed that in 2003, about 8% of the study area has more than 60% vegetation, while in 2017 this amount of vegetation is only about 0.2% of the area. The study concluded that this reduction in vegetation over time could increase the risk of soil erosion. In the study of land use changes, it was found that agricultural and residential use has increased by 37%, and in this regard, it seems that land use changes can also lead to increased soil erosion in the region. Based on the analysis of the interaction of the studied parameters in the preparation of the erosion risk map, it was found that the amount of moderate to extremely severe erosion risk zones has increased by about 20% in the study period in the study area. In soil erosion studies, the risk of erosion usually determines the relative probability of erosion occurring in one site compared to other sites by qualitatively analyzing the interaction of impact factors, Therefore, the results of this study can be a basis for government organizations in order to prioritize the implementation of soil protection activities, allocation of funds and land management.