كليدواژه :
بيابان زايي , پهنه بندي , رفتار بيابان , كوير حاج علي قلي , مدل سازي ژيومورفولوژيكي
چكيده فارسي :
روند فزاينده بياباني زايي در اقصي نقاط ايران، يكي از جدّي ترين معضلات زيست محيطي، اقتصادي و اجتماعي است كه كنترل آن از دغدغه هاي ملي محسوب مي گردد. بنابراين ارزيابي عوامل موثر، شناسايي دامنه تاثير آنها و مدل سازي رفتار بيابان مي‌تواند در پيش بيني روند آتي و جلوگيري از گسترش بيابان زايي مفيد واقع شود. لذا هدف از اين پژوهش مدل سازي ژيومورفولوژيكي و پهنه بندي رخداد بيابان زايي حوضه كوير حاج علي قلي با استفاده از مدل هاي آماري و تكنيك سيستم اطلاعات جغرافيايي است. بدين منظور ابتدا لايه هاي رقومي پارامترهاي ژيومورفولوژي نظير جنس مواد، واحدهاي ژيومورفيك، كلاس هاي فرسايشي، طبقات ارتفاعي، شيب و جهت شيب تهيه، و با لايه بيابان زايي منطقه تلاقي داده شد. پس از تشكيل پايگاه داده از طريق محاسبه مساحت واحدهاي همگن، مبادرت به رابطه سنجي بين پارامترهاي ژيومورفيك و طبقات بالفعل بيابان زايي گرديد و مقادير برآورد شده ي ضريب تبيين به عنوان دامنه تاثير پارامترها در فرايند تخريب اراضي لحاظ گرديد. نهايتاً جهت پهنه بندي رخداد بيابان زايي، لايه هاي رستري پارامترها براساس دامنه تاثير و مدل گام به گام بايكديگر تلفيق، و نتايج مورد ارزيابي دقت قرار گرفت. نتايج دربردارنده نقشه پهنه بندي منطقه مطالعاتي از پهنه خيلي شديد تا پهنه فاقد بيابان زايي مي باشد، بطوريكه پهنه بيابان زايي خيلي شديد وسعتي معادل 32/482 كيلومتر مربع (75/65 درصد) از تخريب اراضي فعلي را به خود اختصاص داده و امكان افزايش مساحت تا 85/2412 كيلومتر مربع را دارد. پهنه بيابان زايي شديد نيز كه 47/184 كيلومتر مربع (14/25 درصد) از وسعت تخريب اراضي فعلي را در برگرفته، مي تواند تا 92/3023 كيلومتر مربع توسعه يابد. نتايج حاصل از اعتبارسنجي مدل و نقشه پهنه بندي، روند نزولي شاخص ارزيابي دقت را از پهنه خيلي شديد به پهنه فاقد بيايان-زايي نشان داده و بيانگر دقت لازم مي باشد. در مجموع حوضه كوير حاج علي قلي از منظر تخريب اراضي بر مبناي پارامترهاي ژيومورفيك يك اكوسيستم ناسالم بوده و داراي رفتار ناهنجار است كه تنش هاي ناشي از افزايش رخداد بيابان زايي را مي توان عامل اصلي ناسالمي سيستم و ناهنجاري رفتار آن برشمرد.
چكيده لاتين :
Introduction
Desertification is defined as land degradation in arid, semiarid and dry sub-humid areas due to climate variation and/or human activity. Land degradation is defined as the reduction or loss of the biological or economic productivity and complexity of agricultural land (including rainfed cropland, irrigated cropland, range and pasture), forests and woodlands. The term implies a negative change with respect to previous environmental conditions, often implicitly considered as the normal or desirable state of affairs in the ecosystem in terms of its use and management.
Ascending trend of desertification is one of the most serious environmental, economic and social issues in most parts of Iran that its control is considered as a national concern. Therefore assessment of effective factors, identification of their influence and modeling of desert behavior can be useful to we predict the future trend of desertification and prevent from its development.
The aims of this study are geomorphological modeling and zoning of desertification by statistical techniques and Geographic Information System in the basin of Haj Ali Gholi Playa.
Materials and Methods
The study area is the Haj Ali Gholi playa in the Semnan Province, central Iran, which is ranged from longitudes 53°15? to 56°E and latitudes 35°15? to 37°N (Fig. 1). This playa is a tectonic plate and sedimentary hole, which is influenced by different geomorphic and climatic morphogenesis process. The shortage of vegetation and moisture lead to the domination of wind processes over other processes in the basin. Thus several types of wind erosion landforms are observed in the region. The basin is a dry-lands landscape that is formed from Mountains, Glacis plains and Playa landviews. Study area, with an approximate area of 18070.918 km2, is located between Toroud-Chah Shirin Horst having 2319m elevation, and Alborz Mountains having 3884m elevation. Its general slope is to the center of playa with elevation 1028m.
To achieve to the purpose, first, digital layers of geomorphological parameters such as lithology, geomorphic units, erosional classes, elevation classes, slope and aspect were prepared and were intersected with present desertification layer by union method. After formation of data base via area calculation of homogenous units, relationships between the parameters were studied, and their determination indexes were computed as influence range of parameters in the land degradation process. Finally, for zoning of the desertification event, raster layers of parameters were combined together according to determination index and Stepwise model, and its result was evaluated.
Findings and Results
The results are included the zonation map of desertification in study area from very high zone to no-desertification zone. So that, the very high desertification zone is included about 482.32 km2 (%65.75) of present land degradation area, and it is possible that increases to 2412.85 km2. Also, the high desertification zone that covering about 184.47 km2 (%25.14) of present land degradation area, can develop to 3023.92 km2. The obtained results from validation test of the model show the descending trend of accuracy assessment index from the very high desertification zone to the no-desertification zone, which represents necessary accuracy of aforesaid model.
Conclusion
Study area is exposed to high-risk of desertification that will convert to a national and regional issue in the near future, if it is neglected, and its negative consequences will affect the quality of life all human, caltural and economic institutions of the area.
