پایش تغییرات پهنه‌های فرسایشی با استفاده از تصاویر ماهواره‌ای طی دوره‌های پر آبی، نرمال و کم آبی (مطالعه موردی: منطقه‌ی نیمروز سیستان)

یکی از مشکلات مناطق خشک از جمله سیستان، تخریب و فرسایش است که علت آن کمبود پوشش گیاهی و بهره برداری نامعقول از عرصه های طبیعی است. هدف از اجرای این پژوهش، پایش تغییرات پهنه‌های در معرض فرسایش بادی در منطقه‌ ی نیمروز سیستان طی سال‌های کم آبی، نرمال و پر آبی است؛ بدین منظور در ابتدا با استفاده از روش‌های ریزمقیاس نمایی، به تهیه ی سری زمانی تصاویر ماهواره‌های با قدرت تفکیک مکانی و زمانی بالا با استفاده از تصاویر ماهواره ی لندست و مودیس پرداخته شد. سپس با استفاده از مدل estarfm، تصاویر مربوط به سال های کم آبی (2001)، نرمال (2008) و پرآبی (2019) شبیه ‌سازی شد. برای پایش تغییرات پهنه‌های فرسایشی نیز نقشه ‌ی کاربری اراضی مربوط به سال‌های کم آبی (1380)، نرمال (1387) و پر آبی (1398) استخراج و با ارزیابی صحت طبقه‌‌بندی این نقشه‌ها، عملیات آشکارسازی تغییرات با استفاده از روش مقایسه پس از طبقه‌بندی برای این نقشه‌ها انجام شد. در بررسی تغییرات پهنه‌های فرسایشی، یافته‌ها نشان داد که طی دوره ی کم آبی تا نرمال، بیشترین درصد تغییرات (35.84 درصد) مربوط به تبدیل اراضی بایر به پهنه‌‌های فرسایشی با مساحتی حدود 32708.68 هکتار و در رتبه ی بعدی، مربوط به تبدیل پهنه‌های فرسایشی به اراضی مرتعی با پوشش گیاهی کمتر از 10 درصد (25.24 درصد) است. همچنین نتایج نشان داد که طی دوره ی کم آبی تا پرآبی، بیشترین درصد تغییرات به ترتیب برابر با 25.38 و 25.98 درصد بود و به تبدیل پهنه‌های فرسایشی به پهنه‌های آبی و مرتع اختصاص داشت. همچنین نتایج بیانگر آن است که طی دوره ی پرآبی با افزایش سطح پهنه‌های سیل ‌گیر در منطقه ‌ی مورد مطالعه، وسعت پهنه‌های فرسایشی نسبت به دوره ی کم آبی60 درصد (معادل با 8059.36 هکتار) کاهش یافت. نتایج نشان داد که تغییر شرایط هیدرولوژیکی جریان‌های ورودی به سیستان، در وسعت پهنه‌های فرسایشی منطقه نقش بارزی داشت که بهبود شرایط آن نیازمند مطالبه ی حق آبه منطقه ‌ی سیستان از کشور افغانستان است.

Monitoring Changes in Erosion areas Using Remote sensing Data in Three years of Wet, Normal and Drought (Case study: Nimroz Region of Sistan)

Extended abstract1 IntroductionWater scarcity is currently one of the worldchr('39')s challenges, especially in arid and semiarid regions; This is because population growth and rising living standards require more food and water. Therefore, excessive use of natural resources has led to the destruction of potential agricultural lands and natural resources. The final process is floods, dust, and desertification, as a large part of the fertile agricultural lands have been affected by erosion and have been removed from agricultural use and farmer has migrated to other places. As a result, rural farmers have migrated to other areas due to a lack of income. According to the reports, by climate and land use change, desertification affected 6% of the worldchr('39')s arid regions from 1982 to 2015. Such a process in arid ecosystems has led to the development of soil erosion hotspots. Numerous studies have been conducted by national and international researchers on drought and its impact on water resources. Therefore, changes in the hydrological cycle and the impact on water resources have a significant role in land use and natural ecosystemschr('39') sustainability. Hence to the importance of studying land use changes and determining erosion areas that provides a good basis for control and stabilization of erosion centers in these areas. This study aimed to investigate landuse changes and erosion areas by simulating time series images with a high spatial and temporal resolution during periods of water scarcity, normal and wet in the Nimroz region of Sistan.2 MethodologyThe study area is located in the north of Sistan and Baluchestan province and part of Nimroz city and the southern part of Hamoon Lake and borders with Afghanistan and at about 480 meters above sea level. This area is mostly flat and lacks topography and natural features. The average rainfall in this area is 50 mm, that most of which falls in winter. One of the Sistan regionchr('39')s characteristics is 120day winds, which sometimes reach speeds of more than 120 kilometers per hour, accompanied by much dust. The development of the Sistan region depends on the water inflow from the Helmand River for 1,200 km, which originates from the mountains of northern Afghanistan. For this purpose, at first, using microscale exponential methods, time series of satellite images with high spatial and temporal resolution were prepared using Landsat and Modis satellite images. To monitor the changes in erosion region, land use maps related to the years of water scarcity (2002), normal (2009), and floods (2019) were extracted, and by evaluating the classification accuracy of the maps, change detection operations were performed using the postclassification comparison method for these maps. 3 Results The results shows that the during the period of water shortage to normal, the highest percentage of changes (35.84%) related to the conversion of barren lands to erosion areas with an area of ​​about 32708.68 hectares. The next rank related to conversion of erosion areas to lands Rangeland with vegetation is less than 10% (25.24%).The results also show that during the water shortage to wet, the highest percentage of changes is equal to 25.38 and 25.98%, respectively, and are related to the conversion of erosion area to water and rangeland area. The results also show that during the flood period, with the increase of floodplain areas in the study area, the area of ​​erosion region has decreased by 60% compared to the water shortage period (equivalent to 8059.36 hectares).4 Discussion Conclusions Due to the dry climate and low rainfall in Sistan, floods from Afghanistan only meet the water needs of the regionchr('39')s ecosystems. By studying the volume of incoming floods during periods of water shortage, normal and high water, the results showed significant fluctuations in the volume of incoming floods to the Sistan region during the studied periods. Since land use is more affected by climatic and hydrological factors, they play a significant role in land use changes. The results shows that the during the period of water shortage, more than 46% of the study area is eroded region, which has been mainly related to the conversion of barren landscapes, dried bed of Hamoon wetland, and flood agricultural lands to these areas.Therefore, it can be concluded that the changes in the hydrological conditions of inflows to the Sistan region play an important role in the extent of erosion areas with respect to the water needs of waterdependent ecosystems. Despite the environmental crises in Sistan region and its regression, the improvement of environmental conditions in Sistan region requires the demand of water rights in Sistan region from Afghanistan.