ارزيابي و پيش بيني تغييرات بيابان زايي در شرق و جنوب اصفهان با مدل CA-Markov

Assessment and forecasting the desertification changes in the east and south of Isfahan by CA-Markov model

يكي از مهمترين بلايايي كه مناطق خشك و نيمه خشك را تحت تاثير قرار مي دهد و در زمره عوامل تهديد كننده حيات بشري و تخريب منابع طبيعي محسوب مي شود بيابان زايي است، بنابراين شناخت و پيش بيني اين پديده از اهميت بسزايي برخوردار است. در اين راستا به منظور بررسي وضعيت بيابان زايي منطقه شرق و جنوب اصفهان از تصاوير ماهواره لندست 4 و 7 و 8 در 5 دوره 1986، 1994، 2000، 2008 و 2016 استفاده گرديد. شاخص NDVI براي شناسايي پوشش گياهي و شاخص شوري خاك براي شناسايي مناطق بياباني و شور به كار گرفته شد. به منظور شناسايي و تهيه نقشه كاربري هاي منطقه مطالعاتي مشتمل بر( اراضي بياباني و شور، پوشش گياهي، شهر، زمين هاي باير و گاوخوني) از روش طبقه بندي نظارت شدهFuzzy ARTMAP و براي محاسبه تغييرات در كاربري هاي پهنه مورد بررسي در 5 دوره فوق از مدل LCM بهره گرفته شد. در ادامه، مدل تركيبي زنجيره ماركوف و سلولهاي خودكار (CA-Markov) براي پيش بيني تغييرات كاربري اراضي استفاده گرديد. براي تعيين اعتبار پيش بيني نيز از شاخص انطباق كاپا بهره گرفته شد كه ميزان 78 درصد را نشان مي دهد. نتايج اين پژوهش نشان داد كه بيشترين تغييرات در طي دوره مورد مطالعه را پوشش گياهي داشته است. اين حجم تغيير طي دوره 1986-1994 بوده است كه 1062 كيلومتر مربع كاهش را نشان مي دهد. از طرفي بيشترين شدت افزايش مناطق شور و بياباني طي دوره 1994-2000 رخ داده كه حدود 495 كيلومتر مربع افزايش را نشان مي دهد. در نهايت مشخص گرديد كه بيشترين تغييرات طي دوره 2016-2024 در پوشش گياهي رخ خواهد داد كه حدود 60 درصد از پوشش گياهي منطقه از بين خواهد رفت و اراضي باير جايگزين آن خواهد شد. اراضي شور و بياباني نيز جايگزين حدود 3/3 درصد از اراضي باير، حدود 1 درصد از پوشش گياهي و كمتر از 0/01 درصد از شهر و تالاب گاوخوني مي گردد.

One of the most important calamities that affect the arid and semi- arid regions and is taken into account as threatening factors for human- life and destroying the natural resources is desertification، so recognizing and forecasting this phenomenon is very important. Desertification is a complex phenomenon، which as environmental، socio-economical، and cultural impacts on natural resources. In recent years، the issues of desertification and desert growth have been stated as important debate on global، regional and national levels and extensive activities have been carried out to control and reduce the its consequences. Desertification is considered as the third important global challenge in the 21th century after two challenges of climate change and scarcity of fresh water. At present، desertification as a problem، involves many countries، especially developing countries and includes some processes that caused by natural factors as well as human incorrect activities. In the other word، Desertification is the ecological and biological reduction of land that maybe occur naturally or unnaturally. The desertification process influences the arid and semiarid regions essentially and decrease the lands efficiency with increment speeds. The study area is located in the east and south of Isfahan. This region has been faced to increasing rate of desertification، because of drought، vegetation removal، change of rangelands to dry farming lands، water and wind erosion and lack of proper land management over previous years. Hence، aim of this research is monitor and forecasting of desertification changes in the east and south of Isfahan during the period of (1986-2016). In this research، the Landsat satellite images used as studies base for studying region desertification. Therefore، at first، satellite images of the study area were extracted from United States geological survey(USGS)website during the period of (1986-2016) and data and satellite images of TM5، ETM+ 7 and LDCM8 sensors of Landsat satellite were used which include thermal and spectral bands. In this relation، for studying the desertification condition in the south and east region of Isfahan، the Landsat satellite images of 4، 7 and 8 during 5 periods of 1986، 1994، 2000، 2008 and 2016 have been utilized. After completing the information data base، first، the soil salinity(S1، S2 and S3) and vegetation NDVI indices exerted on the satellite images. According to Fuzzy ARTMAP method، the land use changes during the period of (1986-2016) recognized in the studied region. In the other word، the vegetation NDVI and soil salinity (S1، S2 and S3) indices have been utilized for identifying vegetation and the desert and salty regions. For preparing the region land use map، the Fuzzy ARTMAP supervised classification method have been utilized and 5 land uses(desert and salty lands، vegetation، city، arid and Gavkhouni) in the region were identified by TerrSet software. The changes calculation in region uses during 5 periods accomplished by LCM model. Also، the Markov chain and Cellular automata synthetic model have been utilized for changes forecasting. This research results indicated that the greatest changes during studied period belonged to vegetation. This volume of change had been during 1986- 1994 that indicate 1062 km2 desertification. In the other hand، the greatest intensity of increasing the salty and desert regions have been occurred during 1994-2000 which indicate 495 km2 increasing. The CA- Markov synthetic method have been utilized for forecasting the land uses changes trend، too. In this relation، for assessing the forecast accuracy، the Kappa coefficient have been utilized which indicate 78%. Finally، it has been specified that the greatest changes during 2016-2024 will be in vegetation which about 60% of region vegetation will disappear and arid lands will be replace them. The salty and desert lands will disappear about 1% of vegetation، 3.3% of arid land and less than 0.01% of city and Gavkhouni. During 2016-2024 about 32% of Gavkhouni lagoon area will disappear and arid lands will be replace them.