پديد آورندگان :
روشن ، غلامرضا نويسنده استاديار گروه جغرافيا، دانشگاه گلستان، گرگان , , محمدنژاد آروق ، وحيد نويسنده استاديار گروه جغرافيا، دانشگاه اروميه، اروميه ,
كليدواژه :
درياچهي اروميه , پيشبيني , مدلهاي گردش عمومي جو , بيابانزايي , هيدرولوژي
چكيده فارسي :
هدف از انجام اين پژوهش، مدلسازي تغييرات تراز درياچهي اروميه در بستر گرمايش جهاني است. براي دستيافتن به اين هدف و شبيه سازي مقادير دما و بارش كشور تا سال 2100، از نتايج دو مدل گردش عمومي جوMIROC_3-2_MEDRES و MPI_ECHAM5 و سه طرح فرضي a1b ، a2 و b1 استفاده شده است. در ادامه براي مدلسازي آماري تغييرات تراز درياچهي اروميه با استفاده از روش رگرسيون چند متغيره، از تاثير تغييرات چهار مولفهي مستقل دما، بارش، نوع اقليم (روش دمارتن) و خشكسالي (روش SPI) با تاخير يكساله نسبت به متغير وابسته (تراز درياچه) استفاده شد. آنچه از ميانگين تمام طرحهاي فرضي براي دورهي مطالعاتي 2010 تا 2100 بهدست آمده است، نشان مي دهد كه بهطور ميانگين دما به ميزان 73/0+ درجه سانتيگراد و بارش به مقدار 44/9- ميليمتر نسبت به دورهي مشاهداتي 1968 تا 2009 تغيير خواهند كرد. همچنين ميانگين كلي تمام طرحهاي فرضي تا سال 2100 از كاهش شاخص اقليمي دمارتن به مقدار 10/0- درصد در هر دهه خبر ميدهد. اما آنچه از مدلسازي آماري بهدست آمد، نشاندهندهي بيشترين كاهش تراز آب درياچه بهميزان 73/2- متر در هر دهه تا سال 2100 براي خروجيهاي مدل MPI_ECHAM5 و طرح فرضي a1b و كمترين تغييرات كاهشي تراز درياچه بهميزان 28/2- متر براي مدل و طرح فرضي MPI_ECHAM5/b1 تا سال مورد نظر است. بههرحال آنچه از مجموع تمام طرحهاي فرضي نتيجه شد، وجود روند كاهشي و معنادار تراز آب درياچهي اروميه (ميانگين 50/2- متر) براي هر دهه از سال 2010 تا 2100 است كه مي تواند تاثير بسيار سو و نامناسبي بر محيط زيست درياچه و اطراف آن داشته باشد.
چكيده لاتين :
Extended Abstract
Introduction
Qualitative and quantitative degradation of water resources is one of the major challenges in the way of sustainable development. Features and phenomena in the earth’s surface have been changed over time; the lakes as one of these features and due to having a closed environment are not considered as an exception. Due to climatic changes such as reduced rainfall, increased temperature and also uncontrolled use of surface water resources in watershed areas, distinguished changes are exposed. Monitoring such changes should be considered as an important issue in the national and regional development and natural resource management. Currently, monitoring the coastal areas and extraction of water at different intervals is regarded as an infrastructural research interest due to the significance of coastal zone management and dynamic nature of such sensitive ecological environments.
Due to the ever increasing rate of greenhouse gas emissions, climate warming is expected to be more intensive during the next century. This warming would very much influence natural processes as well as human activities. In general, it is supposed that in low latitudes, like in Iran (25 and 40° N latitude and 44 and 63.5° east longitude), climate change would have some negative influences on the whole society. For example, higher temperatures will increase the energy demand for cooling, reduce the precipitation rate and degrade the water resources.
Global warming is one of the phenomena that affect human activities and environmental elements. One of these phenomena is fluctuation of lake levels that is a result of climatic, geomorphologic and hydrologic patterns. Since the decrease in the area and level of Urmia lake is an important and interesting subject for local researchers, this study tries to model the fluctuation of Urmia lake level, based on global warming
Methodology
To attain this purpose, and in order to simulate the precipitation and temperature values of the country up to the year of 2100, the results of two general models of MIROC_3-2_MEDRES and MPI_ECHAM5 (which are from issuance scenarios family), along with three scenarios, a1b, a2, and b1 have been used. Then, in order to statistically model the lake level fluctuation based on multi – variables regressions, the fluctuation of the temperature, precipitation, climate type (Domarton method), and drought (SPI method), with 1 year retardation ratio to dependent variable (lake level) have been used.
Also in order to study the fluctuations of Urmia Lake surface area, multi temporal Landsat Images (ETM, TM and MSS sensors) over a 34-year period (1976 to 2010) were used (Fig.3). Spectral specifications and spatial resolution of each of the bands of this satellite are presented in Tables 1. In the present study, the coastlines extraction for each year was done in two major steps using the ENVI software. Firstly, geometric and radiometric corrections as well as different filters on the selected images were applied to make the spectral difference of objects more clear. Secondly, supervised classification method has been used to extract coastlines. For this purpose,
Training Areas where appointed across the lake and more than 25Training Areas have been provided in any of the images. All of these Areas have been provided from the lake’s surface area. Selecting a large number of Training Areas goes back to the nature of Urmia water, its depth and sediments
Results and Discussion
However, the results of the statistical modeling show the most decrease in the lake level (-2.73 m per decade) up to the year of 2100, for the outputs of the MPI_ECHAM5 model and a1b scenario, and the least decrease in the lake level (-2.28 m per decade) in the same period for the model and scenario of MPI_ECHAM5/b1. As a result, it was concluded from all the scenarios that there is a decreasing pattern in the lake level (the average of 2.50 meter per decade for the period of 2010 to 2100), that can lead to warmer and drier conditions. Anthropogenic parameters have also accelerated the Lake level decline and play a key role in deteriorating the status. It certainly cannot be stated that the main reason for the decline in lake levels is attributed to the climate change in recent years. But the human factor as one of the main processes, could exacerbate the lowering process of the lake level.
Conclusion
Results show that in spite of the temperature increase about 0.73 C for the period of 2010 to 2100 relative to the period of 1968 to 2009, the precipitation is reduced about -9.44 mm. Also, the average of whole scenarios to 2100 show that Domarton index will be reduced about -.10 percent for each decade, that can change the lake climate type to warmer and drier conditions.
