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جغرافیا و مخاطرات محیطی - پیاپی 23 (پاییز 1396)

نشریه جغرافیا و مخاطرات محیطی
پیاپی 23 (پاییز 1396)

  • بهای روی جلد: 20,000ريال
  • تاریخ انتشار: 1397/02/01
  • تعداد عناوین: 10
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  • پروین میری، علیرضا راشکی، عادل سپهر صفحه 1
    ذرات معلق در هوا نقش مهمی در توازن انرژی زمین و جو ایفا می کنند و به عنوان یک عامل مهم در تعیین تغییرات آب وهوایی شناخته می شوند. هرساله طوفان های گرد و غبار اثرات مخربی بر روی سلامت، مزارع، تاسیسات و اکوسیستم ها می گذارند. خراسان ازجمله مناطقی است که به شدت تحت تاثیر این پدیده قرار دارد و بادهای 120 روزه سیستان از عوامل تشدید کننده این پدیده بخصوص در مناطق شرقی است. یکی از راه های مطالعه این پدیده روش های سنجش ازدوری است. این تحقیق با هدف بررسی تغییرات زمانی و مکانی شاخص های گرد و غبار بر پایه داده های ماهواره ای در منطقه شرق خراسان انجام پذیرفته است. در این پژوهش جهت مطالعه ذرات معلق جو، از شاخص های UVAI،AAOD و AOD استفاده شده است. برای این منظور از داده های سنجنده TOMS بر روی ماهواره Nimbus 7 در سال های 1978 تا 1993 و بر روی ماهواره Earth probe در سال های 1996 تا 2005 و از داده های سنجنده OMI بر روی ماهواره Aura از سال 2004 تا 2014 استفاده شده است. نتایج این پژوهش روند صعودی این شاخص ها را در طی سال های 2014-1978 نشان می دهد. همین طور شاخص UVAI بیشترین میزان ذرات معلق را در سال های 2002، 2008 و 2014 و شاخص های AAOD و AOD بیشترین میزان ذرات معلق را در سال های 2008 و 2014 نشان می دهند.
    کلیدواژگان: شاخص های گرد و غبار، شرق خراسان، سنجنده TOMS، سنجنده OMI
  • داریوش یاراحمدی، سیامک شرفی صفحه 21
    آزادراه خرم آباد- پل زال به عنوان یکی از مهم ترین مسیرهای حمل ونقل جاده ای کشور، با طول 104 کیلومتر در استان لرستان واقع شده است. هدف از این تحقیق که از نوع تحقیقات کاربردی و روش آن توصیفی- تحلیلی و میدانی می باشد، بررسی مخاطرات طبیعی آزادراه خرم آباد- پل زال با رویکرد پدافند غیرعامل است. در این مطالعه از ابزارهای فیزیکی و مفهومی مانند نقشه های توپوگرافی 1:25000، زمین شناسی 1:100000، تصاویر ماهواره ای، GPS، فرم های برداشت اطلاعات میدانی و نرم افزارهایی مانند Arc GIS جهت تحلیل داده ها و نتیجه گیری استفاده شده است. نتایج حاصل از تحقیق نشان می دهد که رخداد خطر زمین لغزش و ریزش های فعال در مسیر مورد مطالعه مهم ترین تهدید برای مسیر و تاسیسات احداث شده در طول مسیر بوده و مهم ترین عامل در رخداد آن ها، ویژگی های سنگ شناسی است. بررسی و اولویت بندی آزادراه ازنظر مخاطرات ذکر شده حاکی از این است که 5/42 کیلومتر از مسیر در معرض زمین لغزش و 7/23 کیلومتر در معرض ریزش های خطرناک (فعال) قرار دارند؛ بنابراین مسیر آزادراه ازنظر مخاطرات طبیعی با رویکرد پدافند غیرعامل، دارای وضعیت مطلوبی نیست.
    کلیدواژگان: زمین لغزش، ریزش، آزادراه، پدافند غیرعامل، خرم آباد، پل زال
  • محمد امین حیدری، فرامرز خوش اخلاق صفحه 47
    در رخداد ناهنجاری های آب وهوایی، نوسانات جوی و اقیانوسی جوی و اقیانوسی موثر هستند. یکی از انواع مهم این ناهنجاری ها دماهای ناهنجار و گرماهای کم سابقه به ویژه در فصل گرم سال است. برخی از چرخه های جوی و اقیانوسی در فزونی و تشدید ناهنجاری دما در این فصل موثر هستند. این پژوهش با هدف مدل سازی وایازی ارتباط مهم ترین شاخص های اقیانوسی و جوی با ناهنجاری های فراگیر دمای هوا در فصل گرم سال (ابتدای ماه مه تا انتهای ماه سپتامبر) در پهنه ایران انجام شده است. در این پژوهش رابطه همبستگی و توابع بهینه وایازی بین 17 شاخص جوی و اقیانوسی و مقادیر استاندارد شده دما در 30 ایستگاه همدید کشور با دوره آماری بیش از 50 سال داده (1961-2010) و با روش پیرسون و در چهارگام زمانی متفاوت (به ترتیب گام همزمان، یک، دو و سه ماه پیشتر) به منظور تبیین و پیش بینی ناهنجاری دمای هوا در ایران ارائه شده است. بر این اساس تحلیل همبستگی عددی بین شاخص های مورد بررسی و ناهنجاری دمایی ایستگاه ها در فصل گرم سال در پهنه ایران نشان داد، شاخص های NINO3، NINO1+2، NINO3.4، NINO4، GBI، GLOBAL MEAN TEMPERATURE، از مهم ترین شاخص های اقیانوسی-جوی مرتبط با ناهنجاری دمایی فصل گرم در منطقه مورد مطالعه هستند. همچنین در این پژوهش توابع وایازی خطی برای ارتباط شاخص ها و ناهنجاری ماهانه و متوسط دمای ایران ارائه گردیده، که به وسیله آن می توان تغییرات دمایی ایران را تبیین و پیش بینی کرد. صحت عملکرد این توابع با استفاده از مطابقت داده های واقعی و مدل سازی شده (برآورد مقادیر r همبستگی، مقدار RMSE وMBE) با میزان اریبی قابل قبولی مورد تایید قرار گرفته است.
    کلیدواژگان: مدل سازی آماری، وایازی چندمتغیره، ناهنجاری دما، شاخص های پیوند از دور، ایران
  • سودابه بهیان مطلق، مهدی پژوهش، خدایار عبدالهی صفحه 67
    استفاده از مدل های هیدرولوژیکی یکی از روش های رایج در تجزیه وتحلیل کمی حوضه های آبخیز است. پیشرفت های اخیر در زمینه سازی های بارش –رواناب که انعطاف بیشتری در حل مسائل و پدیده های هیدرولوژیکی دارند، آن ها را جایگزین مناسبی به جای روابط تجربی کرده است. به طور مرسوم در پژوهش های صورت گرفته پیشین مبتنی بر بهینه سازی مدل در همان مقیاس محلی موردبررسی قرارگرفته که فاقد عمومیت مکانی است. هدف این مطالعه ارائه پارامترهایی با اندازه معین است تا در سطح عمومی تری برای تمام زیرحوضه ها پاسخ قابل قبولی را ارائه دهد. بدین منظور پارامترهایی از مدل هیدرو گراف سیلاب که در هیدروگراف سیلاب نقش دارند، در مقیاس زیرحوضه ای و بزرگ مقیاس مورد مقایسه قرارگرفته است. در این مطالعه از مدلHEC-HMSبرای مدل سازی رواناب زیر حوضه ها و میزان رواناب خروجی از حوضه استفاده شده است؛ برای ساختار مدل از عوامل شماره منحنی SCS برای روش تلفات و هیدروگراف واحد SCS جهت روش انتقال استفاده شد. به منظور واسنجی ابتدا بهینه سازی پارامترها در هریک از زیرحوضه ها به صورت جداگانه انجام گرفت و سپس مقدار عمومی پارامترها با به دست آوردن اندازه ثابتی از پارامترهای حساس که در همه زیر حوضه ها پاسخ قابل قبولی ارائه دهند، انجام شد. یافته های تحقیق نشان می دهد که گرچه کارایی مدل در واسنجی با پارامترهای محلی برتر از واسنجی با استفاده از پارامترهای بزرگ مقیاس است، ولی ایستایی پارامترهای عمومی بهتر است. به منظور ارزیابی کارایی مدل از شاخص Nash-sutcliffeاستفاده گردید که این شاخص برای کالیبراسیون محلی 85/0 و کالیبراسیون بزرگ مقیاس 65/0 به دست آمد که در دامنه مطلوبی برای شبیه سازی قرار دارد.
    کلیدواژگان: مقیاس محلی، بزرگ مقیاس، مدل هیدرولوژیکی، HEC، HMS، SCS
  • فریبا همتی، داود مختاری، شهرام روستایی، بهزاد زمانی چمنی صفحه 85
    رشته کوه بزغوش در شمال غرب ایران و بین استان آذربایجان شرقی و اردبیل با روند شرقی- غربی در مختصات بین 00 °48 تا 30 °47 درجه طول شرقی و 00 °38 تا 30 °37 درجه عرض شمالی قرار دارد. در این پژوهش رفتار گسل بناروان مورد بررسی قرار می گیرد و هدف از این پژوهش درک بهتری از رفتار تکتونیکی گسل، بررسی اثرات تکتونیک در تکامل چشم انداز و تجزیه وتحلیل مورفولوژی است. به منظور به دست آوردن اطلاعات بیشتر در مورد فعالیت نئوتکتونیک، ویژگی های ژئومورفولوژیکی فعالیت گسل بر اساس ارزیابی سیستم زهکشی رودخانه، ژئومورفولوژی پرتگاه ها و جبهه های کوهستان بر اساس روش های ارزیابی حرکات تکتونیکی فعال مورد مطالعه قرار گرفته است. در این مطالعه با استفاده از شاخص Iat، ارزیابی نسبی فعالیت های تکتونیکی در محدوده گسل بناروان در دامنه جنوبی رشته کوه بزغوش انجام شد. برای برآورد شاخص Iat، هفت شاخص ژئومورفیک شامل: منحنی های هیپسومتری و انتگرال هیپسومتری (Hi)، شاخص عدم تقارن حوضه زهکشی (فاکتور عدم تقارن)(AF)، فاکتور تقارن توپوگرافی عرضی (T)، شاخص طول جریان رود به شیب رود (SL)، نسبت پهنای کف دره به ارتفاع (VF)، شاخص نسبت (V) و نسبت شکل حوضه زهکشی (BS) محاسبه شد. شاخص Iat، فعالیت های تکتونیکی منطقه را در سه کلاس، فعالیت های بسیار زیاد، زیاد و متوسط طبقه بندی کرد. بر اساس این شاخص در منطقه، حوضه ای که دارای فعالیت های کم باشد، وجود ندارد. با توجه به نقشه پهنه بندی فعال ترین منطقه زیر حوضه 2 و کمترین فعالیت در زیر حوضه های شماره 3، 4 و 7 مشاهده می شود. مطالعه و ارزیابی شاخص های مختلف ژئومورفیک در منطقه مورد مطالعه بر روی 8 زیر حوضه در منطقه مورد مطالعه نشان می دهد که منطقه از لحاظ فعالیت های نئوتکتونیکی با تکتونیک جوان فعال می باشد؛ منتهی میزان فعالیت در همه جای آن یکسان نیست. در زیر حوضه شماره 2 فعالیت های جوان بیشتر از سایر زیر حوضه هاست. علت آن را می توان به فعالیت بیشتر گسل اصلی و گسل های فرعی که موجب بالاآمدگی منطقه شده است، نسبت داد.
    کلیدواژگان: ارزیابی نئوتکتونیکی، شاخصه های ریخت سنجی، گسل بناروان
  • حسین عساکره، علی شاهبایی کوتنایی صفحه 109
    در پژوهش حاضر تلاش شده با استفاده از رویکرد محیطی به گردشی، الگوهای همدید توام با موج های سرمای زمستانی در ایران شناسایی شود. براین اساس با استفاده از داده های میان یابی شده دمای کمینه برای زمستان های 1339 تا 1388 ضمن شناسایی روزهای همراه با سرمای فراگیر، داده های جوی شامل فشار تراز دریا و ارتفاع ژئوپتانسیل تراز 500 هکتوپاسکال برای شناسایی الگوهای جوی همراه با موج-های سرمای فراگیر زمستانه در ایران بکار گرفته شد. با انجام تحلیل خوشه ایبر روی داده های فشار تراز دریا طی 487 روز همراه با سرمای فراگیر، درنهایت 5 الگوی همدید تشخیص داده شد. بررسی این الگوها نشان داد که تمامی موج های سرمای فراگیر در پهنه کشور با تکوین یک الگوی پرفشار گسترده بر روی ایران و مناطق همجوار آن توام بوده است. برهمکنش سامانه های پرفشار سیبری و پرفشارهای اروپایی با کم فشارهای جنب قطبی در انتقال هوای سرد از نواحی قطبی و شمال اسکاندیناوی به عرض-های جنوبی نقش مهمی داشته است. همچنین استقرار پشته ها و سامانه های بندالی تراز میانی جو در بخش های مرکزی و شرقی اروپا و استقرار ناوه شرقی آن ها بر روی ایران با ریزش هوای سرد به قسمت عقب این ناوه توام بوده و در ایجاد و تداوم موج های سرمایی در سطح کشور تاثیر زیادی داشته است.
    کلیدواژگان: موج سرمای فراگیر، تحلیل خوشه ای، اقلیم شناسی همدید، سامانه بندالی، ایران
  • مسیب حشمتی، محمد قیطوری، مراد شیخ ویسی، محمود عربدخدری، مجید حسینی صفحه 125
    جنگل های بلوط زاگرس نقش ارزنده‏ای در تغذیه آب های زیر زمینی، پایداری کشاورزی، حفاظت خاک و کنترل سیل دارند. بااین وجود، تغییرات اقلیمی از جمله کاهش بارش موجب خشکیدگی بخش قابل توجهی از این منابع ارزشمند شده است. هدف از اجرای این تحقیق یافتن رویکردهای مناسب سازگاری با تغییرات اقلیمی به‏منظور کاهش شدت خشکیدگی درختان جنگلی از طریق استحصال آب باران و ذخیره آن در خاک بود که در بخشی از جنگل‏های استان کرمانشاه در قالب طرح آزمایشی بلوک های کامل تصادفی انجام یافت. تیمارهای مورد آزمایش شامل بانکت+قرق، قرق، بانکت بدون قرق و شاهد با سه تکرار بودند. بانکت‏ها به طور منقطع و هلالی شکل به‏طول 7 متر و فاصله تقریبی چهار متر به شکل زیگزاکی ایجاد شدند. نتایج این تحقیق نشان داد که اعمال تیمار بانکت+قرق بعد از سه سال، موجب کاهش خشکیدگی 37 پایه و احیای 19 پایه در هکتار (در مقایسه با تیمار شاهد) گردید (درمجموع 57 پایه). تیمار قرق گرچه موجب احیای پایه های خشکیده نگردید، اما موجب کاهش تشدید خشکیدگی به تعداد 38 پایه در هکتار گردید. تاثیر تیمار بانکت بدون قرق منجر به کاهش خشکیدگی به تعداد شش پایه در هکتار به دلیل عدم حفاظت و چرای دام شد. نهایتا افزایش معنی‏دار کربن آلی خاک و بهبود جرم مخصوص ظاهری نیز بر اثر اعمال تیمارهای بانکت و قرق به دست آمد که به نوبه خود منجر به افزایش ظرفیت ذخیره رطوبت خاک شدند. بر اساس نتایج این تحقیق، فائق آمدن بر خشکیدگی جنگل‏های زاگرس مستلزم مدیریت مستقیم و جامع جنگل‏ها با رویکردهایی مبتنی بر سازگاری با شرایط خشکسالی و حذف عوامل تخریب، به ویژه عوامل برهم زدن نیمرخ خاک مانند شخم و کاربرد ماشین‏آلات سنگین در عرصه های جنگلی است. اساس این رویکردها حفظ رطوبت خاک، سازگاری با شرایط خشکسالی، حذف عوامل تشدید خشکیدگی درختان جنگلی و تداوم پژوهش های بیشتر است.
    کلیدواژگان: بانکت های هلالی، خشکیدگی بلوط، رویکردهای سازگاری، رطوبت خاک
  • امید مفاخری، محمد سلیقه، بهلول علیجانی، مهری اکبری صفحه 143
    پایین بودن میزان ریزش های جوی، تغییرپذیری بالا، نوسان بارش، از ویژگی بارز آب وهوای ایران به شمار می رود. هدف این پژوهش مطالعه و بررسی تغییرات تعداد روزهای بارشی، مقدار بارش و تغییرات شدت بارش در بلند مدت در نواحی مختلف ایران است. داده های بارش روزانه در طی دوره آماری 30 سال از سازمان هواشناسی کشور برای 53 ایستگاه همدید در نقاط مختلف ایران گرد آوری شد. جهت طبقه بندی از نظر دوره تداوم بارش، روزهای بارشی در 7 طبقه، بارش 1 روزه، بارش با توالی دو روز، بارش با توالی سه روز الی بارش با توالی 7 روز بررسی و استخراج گردید. برای تحقق اهداف از روش تحلیل خوشه ای(فاصله اقلیدسی و روش ادغام وارد) برای ناحیه بندی اقلیمی استفاده شد و درنهایت ایران به هفت ناحیه از نظر متغیرهای تعداد روز بارشی تقسیم گردید. سپس دوره مطالعاتی به دو دوره 15 ساله جهت مقایسه تقسیم شد. برای شناسایی شدت بارش روزانه از نسبت بارش حداکثر روزانه به سالانه استفاده شد. نتایج نشان داد که در اغلب نواحی ایران فراوانی روزهای بارشی کوتاه مدت در 15 سال دوم مطالعاتی (2013-1999) نسبت به 15 سال اول (1984-1998) روند افزایشی دارد. این امر نشان می دهد که بارندگی های شدید و رگباری در گستره ایران در حال افزایش است که می تواند ناشی از کاهش تعداد روزهای بارشی به ویژه بارش های میان مدت و بلند مدت (4-5 و بیشتر از شش روز) باشد و بیشینه بارش در کوتاه مدت (بارش 1- 3 روز) اتفاق می افتد.
    کلیدواژگان: مخاطرات بارش، تغییرات بارش، بارش روزانه، توالی بارش، رگبار
  • نگار سیبانی، سید حسین ثنایی نژاد، بیژن قهرمان صفحه 163
    در مواجه با خطر سیل و یا خسارات ناشی از خشکسالی، برآورد میزان بارش و الگوی تغییرات مکانی آن در یک منطقه گسترده، یکی از چالش های مهم در علوم هواشناسی، کشاورزی و هیدرولوژی است. اندازه گیری محلی بارندگی در مناطق دور افتاده به دلیل هزینه زیاد و محدودیت های عملیاتی دشوار است. بدین علت در تحقیق حاضر به منظور تعیین الگوی مکانی-زمانی بارش و امکان تلفیق داده ها، سه نوع مختلف از تولیدات بارندگی شامل داده های ماهواره ای (TRMM3B42)، داده های حاصل از مدل پیش بینی عددی جوی (MM5) و اندازه گیری های زمینی (نقشه های حاصل از روش زمین آمار (KED))، مورد مطالعه قرار گرفتند. این مطالعه در بازه زمانی سال های 2000 تا 2010 میلادی و برای منطقه شمال شرق ایران به صورت ماهانه، فصلی و سالانه انجام شد. داده ها با استفاده از شاخص اعتبارسنجی RMSE و الگوریتم تشابه با یکدیگر مقایسه شدند. نتایج نشان دادند که یکی از ضعف های روش زمین آمار نبودن اطلاعات کافی در ارتفاعات بالای (1500) متر منطقه است. همچنین دقت تصاویر ماهواره ای در فصل های گرم بیشتر بود؛ بطوریکه در ماه آگوست مقدار 7/1 RMSE = به دست آمد. در فصل زمستان (ماه ژانویه) بیشترین مقدار 02/14 RMSE = حاصل شد که این امر عملکرد ضعیف تولیدات ماهواره ای TRMM در مناطق پوشیده از یخ را نشان می دهد. در اعتبارسنجی مدل MM5 بیشترین و کمترین مقدار RMSE به ترتیب 64/6 و 05/1 به دست آمد. علاوه بر این مدل MM5 تا حدود زیادی در شبیه سازی مقادیر بارندگی سالانه بیش برآورد داشت. نتایج تحلیل های مکانی- زمانی الگوریتم تشابه نیز نشان دادند که عملکرد مدل MM5 در مقیاس ماهانه و فصلی و تعیین مناطق بارندگی بهتر از تصاویر ماهواره ای TRMM بود. همچنین هر سه محصول الگوی مکانی بارندگی در مقیاس فصلی و سالانه را به خوبی نشان دادند.
    کلیدواژگان: الگوریتم تشابه، بارندگی، TRMM
  • عبدالرضا کاشکی صفحه 181
    تغییر روند سامانه های کلان مقیاس اقلیمی همچون تاوه قطبی، نقش بسزایی در تغییر اقلیم سطح زمین دارد. در این پژوهش برای نیل به این هدف، از داده های دوباره واکاوی شده ارتفاع ژئوپتانسیل تراز میانی جو از مرکز ملی جو و اقیانوس شناسی ایالات متحده آمریکا استفاده شده است. این داده ها دارای تفکیک مکانی 5/2×5/2 درجه قوسی و به صورت میانگین روزانه برداشت گردیده است. دوره آماری این پژوهش از سال 1948 تا 2007 میلادی برای نیمکره شمالی بوده و شامل 144×36 یاخته است. برای مقایسه میانگین ها، از آزمون تی- تست برای دو گروه وابسته و جهت بررسی روند تاوه قطبی از آزمون روند کندال تاو استفاده گردید. نتایج پژوهش نشان داد که تاوه قطبی در ماه های اردیبهشت، خرداد، تیر، مرداد، شهریور و اسفندماه، دارای روند کاهشی (منفی) در سطح معنی داری 01/0 است. البته علل کاهش سطح تاوه قطبی در نیمه سرد سال و به ویژه در بهمن ماه و اسفندماه نیز قابل تامل است. همچنین در تمام ماه های مورد بررسی، سطح تاوه قطبی کاهش یافته و سیر نزولی داشته که عموما این سیر کاهشی، در نیمه گرم سال بیشتر از نیمه سرد سال است. این تغییرات باعث ناهنجاری در الگوهای آب وهوایی مناطق می گردد.
    کلیدواژگان: قطبی، تحلیل روند، تغییر اقلیم، نیمکره شمالی
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  • Parvin Miria, Alireza Rashkib, Adel Sepehrc Page 1
    1.
    Introduction
    Satellite remote sensing provides an undoubtedly unique opportunity to extract spatial
    patterns of regional, international and seasonal aerosol properties. In order to understand
    the effects of air particles on climate and human health over the lands, it’s necessary to
    have spatial and temporal distribution of aerosol. Ground-based measurement data do not
    provide the spatial pattern of particles and therefore, satellite data are used. Aerosol
    indices such as Aerosol Index (AI) and Aerosol Optical Depth (AOD) are commonly used
    to identify the amount of atmospheric particles. East Khorasan is under the influence of
    dust emission since the strong Levar winds (120-day wind) blow over the region. The aim
    of this study was to investigate the temporal and spatial variability of aerosol in the East
    Khorasan, Iran based on satellite data.
    2. Study Area
    East Khorasan with an area of 100,161 km2 is limited from the north and east to
    Turkmenistan and Afghanistan and from south to Sistan and Baluchistan Province. There
    are 11 meteorological stations at this region including Sarakhs, Mashhad, Torbat-e-
    Heydarieh, Torbat-e-Jam, Taybad, Khaaf, Gonabad, Qaen, Birjand, Sarbishe and
    Nehbandan.
    3. Material and
    Methods
    The Aerosol indices were obtained from TOMS sensors with a spatial resolution
    ( 1° × 1.25° ) and OMI sensors with a spatial resolution ( 0.25° × 0.25° ) from
    http://disc.sci.gsfc.nasa.gov/giovanni. The monthly, seasonal and yearly mean values of
    the data sets were calculated from all available data. To study atmospheric aerosols,
    UVAI, AOD and AAOD indices were used. For this purpose, TOMS sensor data from
    the satellite Nimbus 7 satellite in 1978 and 1993 and in 1996 and 2005 and the Earth
    probe OMI on Aura satellite were used from 2004 to 2014.
    4.
    Results And Discussion
    The results indicated that the amount of particulate matter obtained using UVAI/OMI is
    highest in all cities in June, July and April and lowest in December, November, and
    October. The AAOD related to each city was quite different from other cities and there
    was no specific month which showed the highest or the lowest concentration of absorbing particles; it seems that the UVAI index does not follow a specific pattern while the UV index has the highest amount in Mashhad. Therefore, UV seems to be associated with air pollution. AOD index also had the highest value in the city of Mashhad in May and the lowest value occurred in Tayabad and then in Khaaf in December. Maximum UVAI/TOMS index occurred in June. The OMI sensor has the same monthly pattern as
    the TOMS data. Tayabad had the highest aerosol (UVAI) and Mashhad had the lowest.
    From 2004 to 2014, the amount of aerosol increased in the region. The concept of AAOD is close to UV-absorbing aerosols such as smoke, dust and minerals in all cities increased in the period of 11 years.
    5.
    Conclusion
    According to the results, spatial and temporal variabilities of indices are more associated
    with climate processes and then topography. Low attitude areas have the highest UVAI
    aerosol value while mountainous areas have the lowest amount of UVAI index.
    Keywords: Aerosol indices, East Khorasan, OMI sensor, TOMS Sensor
  • Dariush Yarahmadia, Siyamack Sharafib Page 21
    1.
    Introduction
    Transport network, as a basic infrastructure, is of economic, social, and political importance to any country. Among the various ways of transport (that is, road, rail, air,
    and sea), road transport, due to its unique features, basically is known to be the most
    commonly used one. Nowadays, one of the important ways to bring down an under-attack country is to seriously damage its vital arteries (i.e. roads and transportation ways).
    Therefore, in order to defend a country against such attacks, it is imperative to know how to deal with them. Passive defense, as one of the influential factors in many projects, is one of the most effective and sustainable ways to defend against such threats. It refers to a number of strategies, utilization of which in the design and construction of facilities and biological buildings, automatically increases the defense power of the construction without pressuring the human resources, and, as a result, decreases the possibility of crisis.
    One of the factors contributing to passive defense is paying attention to geological features when locating and routing facilities and constructions. Slope instabilities are among such phenomena that are related to geological features; in addition to road blockage, these instabilities cause the parts on which facilities and structures are built to move and be displaced. Based on the aforementioned argument, it is imperative to consider the geological features while building infrastructures such as roads; it is also crucial to evaluate active geological forms and phenomena, having passive defense in mind, when locating and routing such infrastructures in order to minimize the risk of damage made by geological movements to them. In this regard, Khorram abad-Pole Zal Freeway as the main south-north road artery of the country that has a diverse range of natural hazards due to its geological characteristics is studied using the passive defense
    approach.
    Khorrram abad-Pole Zal Freeway, the area of study, as part of Tehran-Bandar Imam
    Khomeini’s route, has a length of about 104 km. The freeway extends from some parts of
    Lorestan Province (that is, Dore-Chegeni and Poldokhtar) to Andimeshk in Khuzestan
    Province. The path starts from the latitude of 33˚ 25′ and the longitude of 48˚ 12′ east and ends at the latitude of 33˚ 48′ North and the longitude of 48˚ 03′ east.
    2. Material and
    Methods
    The present study has used an applied research type; moreover, for the research
    Method
    of the study, the analytical field studies method was employed. Data were gathered using
    data from both library and field studies methods. Library resources were tapped on in
    order to make theoretical assessments and to develop a theoretical framework of the
    research literature. In the field studies that form the fundamentals of the present research, the freeway was firstly studied to identify the natural hazards that endanger the path.
    Afterwards, using GPS, hazardous places along with places were landslides had occurred
    were identified. The rest of the qualitative and quantitative data from hazardous points
    were collected in field studies. In the present study, physical tools such as geological
    maps of 1: 100000, topographic maps of 1: 25000, digital elevation model with a
    resolution of 30 meters, satellite images (Landsat-Sensor TM and ETM), images of
    Google Earth, conceptual tools such as software Arc GIS, ENVI, Google Earth, and other
    similar software were used to create a database; satellite imagery, spatial analysis and
    map drawing have also been employed in the study.
    After providing the basic information, the hazardous places along with the identified
    hazardous points, according to the data gathered from the field studies, were prioritized
    using Delphi method and the opinion of experts in Geological Sciences. Finally, the
    hazards were analyzed after dividing them into different sections according to their risk
    level.
    3.
    Results And Discussion
    The survey of Khorram abad-Pole Zal Freeway and its surrounding areas indicated that
    mass movements, landslides, and collapses occur frequently in the given areas. Based on
    the field studies, 21 active landslide zones threaten the road. Most landslides occurred in
    the north side of the freeway in poor resistant limestone formations; the geological
    formation, trenching, and tilt have been the most important factors in these occurrences.
    The study of the position of active landslides on the route showed that the most dangerous parts of the freeway in terms of landslide risk are from km 1.5 to km 36 and from km 56 to km 62. Landslides either have not occurred in other parts of the roads or have only had non-threatening volumes. Prioritizing the risks of 21 active landslides, based on the considered factors, indicated that 11 landslides have the highest amount of risk, 3 are highly risky, and 7 are of a moderate risk. These landslides are mainly observed in two
    sectors of the route – the first part is from km 16 to km 36 and the second is from km 57
    to km 60. According to the risk of landslides, the 104 km freeway is divided into 5
    sections. The first section has a length of 1.5 km and is located in the area that has no risk.
    The second section has a length of 36 km and is in a dangerous area. The third section
    has a length of 19 km and is in an area that, in terms of being risky, ranges from slight to
    moderate. The forth section has a length of 6.5 km and is in a dangerous area. The fifth,
    and the last section has a length of 41 km and is located in an area of no risk. Thus, in
    terms of landslide risk, 42.5 km of the freeway is located in dangerous areas and 42.5 km
    of it is situated in areas that have no risk of landslide.
    The risk of rockfall in the freeway was also studied as another natural hazard to the road.
    Based on the field studies, 30 areas of active rockfalls were identified. Most of the active
    rockfalls have occurred in the north slopes with weathered, and mixed soil, bedrock and
    mainly in limestone formations combined with other stones. The identified rockfall areas
    are of high frequency of occurrence in two parts of the freeway. The first section is located in the distance between km 13 to km 20 of the freeway and includes 12 points of rockfall.
    In this section, rockfalls mainly consist of big rocks. The second part is located in the
    distance between km 23 to km 39 of the freeway and includes 12 points of rockfall.
    Rockfalls occur sporadically in other parts of the freeway. The prioritized areas of active
    rockfall, based on the hazard level, indicated that 6 points are of great danger, 18 points
    involve a high risk of rockfall, and 6 points are of medium risk level. Out of the 6 highly
    dangerous areas, 4 are located in the first part of the route (i.e. from km 30 to km 36), and the other two points are located in the second part of the freeway (i.e. from km 63 to km 93). The area of high risk of rockfall is located in the first part of the freeway (i.e. from km 13 to km 19.5) and in the second part of it (i.e. from km 25 to km 39). The areas with medium risk of rockfall are located in different parts of the road, especially at the beginning of the freeway.
    4.
    Conclusion
    Based on the passive defense approach, the survey of Khorram abad-Pole Zal Freeway
    indicated that natural hazards such as landslides and rockfalls have a high frequency of
    occurrence in the area and that these phenomena are serious threats to the 104 km freeway as well as to structures such as tunnels, electric towers, etc. The study and mapping of landslides along the freeway indicated that the landslides are of more abundance and density in two specific sections of the route. The length of the route, considering active and dangerous landslides, is 42.5 km which includes 21 active landslide zones.
    Active areas of rockfall are also of serious threat to the freeway. The classification of the
    route into 7 different sections, based on the risk of rockfalls, showed that 3 sections
    involve no risk, 2 are of medium risk, and 2 are dangerous and highly risky. Accordingly,
    17.2 km of the freeway is located in the risk-free zone, 63.1 km in the zone with moderate risk, and 27.3 km in the danger zone. Moreover, out of the 30 active areas of rockfall along the freeway, 6 points are highly dangerous, 18 have a high risk level, and 6 are of medium risk. Hence there are 24 active areas of rockfall that are of actual risk to the road.
    The results of the study showed that Khorram abad-Pole Zal Freeway is not in an
    acceptable condition from a passive defense point of view. The main reason for this is
    that the geological feature of the area have not been taken into account when designing
    the freeway. Natural hazards such as landslides and active rockfalls, due to overlooking
    the geological features of the area, have blocked, and destroyed, parts of the freeway and structures alongside it.
    Keywords: Freeway, Khorram abad-Pole Zal, Landslides, Passive defense, Rockfall
  • Mohammad Amin Heidari, Faramarz Khoshaghlagh Page 47
    1.
    Introduction
    Climatic variation is one of the inherent features of the climate system. The components
    of the climate system are diverse and complex, so that these components interact with
    each other in a Interweaving way, so that the change in each component eventually
    changes other components as well. The climate indicators are defined to describe the
    status of the climate system and its changes. Each climatic index describes some aspects
    of the climate based on certain parameters. Therefore, various climate indicators have
    been proposed and used in many studies.
    Climatic indices are measurable and computable and correlate with some of the elements
    of the climate in different regions. Some atmospheric variables such as pressure,
    temperature, precipitation and radiation, as well as non-atmospheric parameters such as
    sea surface temperature (SST) or ice cover, are among the factors to be considered for
    climate forcing in different parts of the world. The large water resources, such as seas and oceans, are among the most important climatic operators. These resources are capable of storing a large part of the solar energy and also, due to their fluid nature, are capable of transporting energy to other parts of the planet in various ways (surface flow, subsurface flow, convection, and moisture advection). Changes in ocean behavior, therefore, cause changes in atmospheric patterns, which can further change the short and long-term climatic conditions in different regions. For this reason, ocean surface temperature can be considered as one of the important indicators affecting climatic abnormalities.
    All patterns of teleconnection as natural phenomenas, are resulting from the turbulent
    nature of the atmosphere and its internal energy resources. These patterns represent
    macro-scale variations in atmospheric wave patterns and jetstream flows, and affect the
    distribution of temperature, precipitation, storm paths, and the status and pattern and
    speed of the jetstream in large areas. For this reason, the patterns of teleconnection lead
    to abnormalities that occur simultaneously in very distant areas (Asakere, 2007; 48). In
    fact, the variability of the behavior of the atmosphere is a result of the set of behaviors
    and interactions between the ocean and the atmosphere. Hence, indicators that explain
    the abnormal behaviors of the ocean and therefore the atmosphere can help to identify
    the causes and nature of the occurrence of short and long-term climate abnormalities in
    a region. The study of air temperature anomalies in the warm season in Iran in relation
    to the most important oceanographic and atmospheric indices is the main aim of this
    research.
    2. Material and
    Methods
    In this study, two different databases were used including the data of the IRIMO stations
    and indexes data of oceanographic and atmospheric teleconnection of the NOAA Data
    Center, affiliated to the U.S. Center for Oceanography Studies. The data of the IRIMO
    stations consist of 30 synoptic stations with a period of 50 years of data (1961-2010). In
    the first step, the standardized temperature of each station was calculated per each month during the warm period of the year (from May to September). Then, for the purpose of detecting anomalies, a function was defined in Excel macro as; -0.5 >x> .5, and from among the 250 months examined the anomalies (at least 20 stations from 30 stations), 57 cases with anomalies among whole months were selected in the study period, and then by the Pearson correlation method, a relation was calculated between the 17 selected atmospheric-oceanic indicators and the air temperature. The indicators used in this study are the most important indicators introduced in international studies. Also, by using multivariate regression, optimal parameters and regression functions are presented in order to explain and predict the relationship between indices and temperature anomalies in the warm season in the whole of Iran.
    3.
    Results And Discussion
    The air temperature of Iran shows a significant relationship with the teleconnection
    indexes. According to the tests performed in selective stations, in general, NINO3,
    NINO1, NINO3.4, NINO4, GBI, CAR, PACEFIC WARM POOL and GLOBAL
    MEAN TEMP indexes were have a significant correlation in 90% confidence level. In
    terms of time in calculations with monthly synchronous steps at selected stations, the
    best indexes are GBI, NINO1 2, NINO3 and NINO3.4, with correlations of 0.8, -0.8, -
    0.57 and -0.4, respectively. In terms of a previous step, the GBI, NINO1 and NINO3
    indexes had the highest correlation values of 0.8, -0.8 and -0.5, respectively. The
    temporal pattern of the impact of some indicators, such as NINO, which was mostly
    strong and inversely in the same month, was directly and significantly in the two and
    three months earlier. Based on the results obtained from the multivariate modeling, the
    correlation between the selected teleconnection indexes such as GLOBAL MEAN
    TEMP, GBI, NINO 1 with thermal anomalies in the warm season of Iran are 0.94; as
    the best temperature predictions, and at the same time a month earlier, the NINO3 index
    was added to the above-mentioned indexes. In general, the indexes of NINO3-4,
    NINO3, NINO1, NINO4, and GBI are the best atmospheric and oceanographic
    indicators that predict Iran's temperature anomalies.
    4.
    Conclusion
    According to numerical correlation analysis between the selective indexes and the
    temperature anomalies of the selective stations in the warm season in Iran showed that
    NINO3, NINO1 2, NINO3.4, NINO4, GBI and GLOBAL MEAN TEMPERATURE
    indexes are the most important oceanic-atmospheric predictors. Also, in this paper,
    linear regression functions for the relationship between indices and monthly temperature
    anomalies are presented, which can explain and predict the temperature changes in Iran.
    The correctness of these functions is confirmed by using the actual and modeled data
    (estimating R correlation values, RMSE and MBE values) with an acceptable error rate.
    It should be noted as long as the intervals of predicting are prolonged, apparently the
    importance of atmospheric indexes is reduced and contradictory the number and
    reliability of ocean indexes are increased. In total, using the above mentioned indices
    and using multivariate regression method in each step of time (simultaneously, one, two
    and three months earlier), the linear regression function for the relationship between
    indexes and monthly temperature anomalies of Iran has been presented, which by using
    it the Iran's temperature changes can be predicted finally. It should be noted that the
    functions obtained here are to predict the average temperature of selected stations in
    Iran, and therefore for each station the calculations must be made individually.
    Keywords: Climate Perdition, Modeling, Multivariate Regression, Temperature Anomaly
  • Sodabeh Behyan Motlagha, Mehdi Pajouheshb, Khodayar Abdollahic Page 67
    1.
    Introduction
    Application of hydrological models is one of the common methods for quantitative
    analysis of watersheds. A class of these models is used to simulate rainfall-runoff
    processes. A hydrological rainfall-runoff model deals with integration of time series
    data, operational parameters, local variables and physical governing system laws in
    order to simulate runoff and other processes of the catchment. The flood hydrograph is
    an important graphical representation in hydrological analysis. The shape of hydrograph
    is a direct response to management strategies basin. In fact, watershed management is
    not possible unless hydrological characteristics of the basin could be fully understood.
    HEC-HMS model is a rainfall - runoff model with either a simple lump or a quasidistributed
    structure. The model was developed by Hydrologic Engineering Center of
    US Army Corps of Engineers. One important capability of this model is the possibility
    of its integration with ArcGIS. The HEC-GEOHMS extension automatically calculates
    most of the geospatial data that needs to be calculated manually. Its user-friendly
    interface offers several tools/icons such as the basin, reach, junction, etc. to enter the
    data. The component-based set up of the model makes it possible to modify the
    structure of the modeling system by the user. Different options for calculating the loss
    method, transmission, and streaming flow are available in HEC-HMS model. Each
    element has its own parameters or inputs. This flexible system provides an opportunity
    to apply the model to the regions with limited access to data. For a similar reason,
    models like HEC-HMS are useful tools to investigate the effects of changes in some of
    the spatial and temporal variables. In this study, the effects of the spatial scale on the
    optimization of HEC-HMS have been investigated.
    The modeling parameter sets obtained by large scale setting generally outperform
    local scale hydrologic parameterization. Most research in the field of calibration of
    hydrological models has focused on the local parameters but if the at larger scales, it
    can be regionalized to other places. In such procedures, the sensitivity analysis is initially used to identify the most important parameters. The aim of this study was to
    compare local and large scale calibration.
    2. Material and
    Methods
    Kohsukhteh watershed is geographically located between 50 °40' to 51 ° 20 ' East
    longitude and 31° 20' North and 32 ° latitude. The study area covers an area of 2783
    square kilometers. The minimum and maximum elevation values in this basin are 1705
    and 3398 meters respectively. The average slope of the area is 19%. The mean recorded
    annual precipitation (Shahrekord synoptic station) is 320 mm.
    Data preparation for HEC-GEOHMS was the first stage of modeling. Different physical
    characteristics, base maps and time series data of the basin were introduced to the
    model. The model set up was implemented by setting Loss, Transform and Base-flow
    methods for each sub-basin. The necessary steps for meteorological model and control
    specifications were taken as well. The 6-hour rainfall and 6-hour discharge time series
    were primarily used for the analyses. The model was parameterized at both local and
    large scale levels. Parameters related to Loss method, Transfer method and Routing
    were selected on the basis of model performance. In order to identify the most sensitive
    parameters, sensitivity analysis was performed. Given that the accuracy of the input
    parameters is an indicator of the efficiency of modeling and the results of the final
    simulation, the results depend on this stage. After identifying the sensitive parameters,
    they were selected to optimize the model locally and in a large scale. Despite the
    uncertainties and errors of the models, no computer model can expect a complete and
    accurate prediction. Therefore, they should be calibrated and validated. To evaluate the
    performance of models with different conditions, six events were chosen for the
    calibration and two for validation of the model.
    3.
    Results And Discussion
    Sensitivity analysis on the parameters of the model showed that Lag time parameter and
    initial abstraction had the highest sensitivity. Calibrated values of the model parameters
    were obtained for both calibration and validation events. The results of calibration in six
    events and the observed and simulated runoff volume in the basin were compared. Two
    events were selected to validate the calibrated model. Runoff discharge and volume for
    the basin were simulated. The values obtained by simulation were compared against the
    recorded observational data at the hydrometric stations were compared. After
    calibration and optimization of the model at local scale, the results showed that both
    estimated peak discharge and the time to peak flow, was performed better than obtained values for the basin scale simulation.
    The inter-comparison among the events also show some differences in model
    performance. Event December 25, 2012 showed the highest accuracy and March 30,
    2012 was simulated with the least accuracy. The difference may be due to the change in
    soil permeability during winter time. In the case of large scale model, the Event
    December 25, 2012 was simulated with high efficiency. Lag time, initial abstraction,
    curve number and impervious ratio were identified as the most important factors for calibration. The obtained Nash-Sutcliffe for local calibration was 0.85 while it dropped
    to 0.65 for large scale calibration.
    4.
    Conclusion
    Modeling is an indirect method that is much faster than field methods. In order to
    achieve accurate results in modeling, we need to estimate the model parameters as well
    as the time and place of variables. Calibration refers to the process of comparing of the
    measurements against the estimated values. The use of local scale calibration versus
    large scale calibration has a higher apparent accuracy, and this is in line with
    Samaniego, Kumar and Attinger (2010) and Hundecha and Bárdossy. (2004). However,
    the commutated value for Sutcliffe model efficiency is less variable in the case of local
    calibration. It was demonstrated that the simulated peak runoff was closer to
    observations in local calibration compared to the large scale calibration. A similar
    Result
    was found with the simulated runoff volume using local calibration. Although, both
    calibration settings provided an acceptable response to the estimation of runoff; the
    obtained parameters at basin scale show less spatial sensitivities. This makes it possible
    to generalize the calibration results to nearby areas with limited data. The results show
    that the large-scale parameterization actually has less spatial dependency and therefore
    may provide more reliable results. This finding is in line with reported advantages of
    large-scale parameter estimations, in term of saving the time (Troy, 2008; Pokhrel,
    2008; Beven, 1002). Sensitivity analysis also showed that parameters such as
    imperviousness and initial abstraction had a high sensitivity in the study area.
    Keywords: Global-scale optimization, Hydrological modeling, Local-scale optimization
  • Fariba Hemmatia, Davoud Mokhtarib, Shahram Roostaeic, Behzad Zamani Gharechamanid Page 85
    1.
    Introduction
    There is almost no region in the world that has not undergone tectonic changes during the recent millennia (Keller & Pinter, 2001). For this reason, evaluation and investigation of active tectonic processes and their effects, for example earthquakes, are of vital importance for many human activities including the design and construction of cities,
    power plants, and dams as it helps minimize their risks and damages (Soleymani, 1999).
    The Benaravan fault, located on the east of a mountain, is part of the Mianeh-Ardebil
    fault. The 20 km long Benarvan fault is one of the most significant ones in the region. It
    is located on the southern skirt of Azerbaijan’s Mount Bozgush and extends in the
    southwest-northeastern direction. Its route features special attributes concerning domain
    instabilities and geomorphological phenomena (Monroe & Wicander, 2001). Tectonic
    and geomorphic activities, relatively low-resistance lithology (Miocene era degenerative
    sediments), intense faulting of the region and being located in the very high risk region
    of earthquake (Benarvan fault and adjacent faults), and the high level of subterranean
    waters result in the possibility of natural risks such as earthquake and other types of mass
    movement. The significance of such a research is due to the location of numerous
    residential areas across the Benavran fault. So far, there have been many studies on the
    behavior of faults based on morphotectonic indicators in Iran and the world, the
    Results
    of which indicate the potential of these indicators in analyzing the behavior of faults.
    2. Material and
    Methods
    In this research, the basin was divided into sub-basins initially in order to ease calculations
    and outcome comparisons. Then, using quantitative indicators, the researchers investigated the effects of tectonic activities on the valleys and riverbeds. The bulk of the
    data needed for indicators was acquired from 1:25000 scale topographic maps, especially
    digital and aerial maps (Keller & Pinter, 2002). The morphological indicators used for
    the region are the following: hypsometric curves and integrals, asymmetry index of the
    drainage area (asymmetry factor), symmetry factor of the transverse topography, stream
    length gradient index (SL), valley width to height ratio (VF), the V ratio, and drainage
    basin shape ratio (BS). After calculating the geomorphic indicators of the studied area,
    the researchers estimated the tectonic activities using the IAT index. The IAT index is
    obtained from the mean value of different geomorphic indicator classes.
    3.
    Results And Discussion
    In this research, the waterways and the basin border were marked using a 1:25000 and
    1:100000 scale geologic maps, respectively.
    3.1. The hypsometric curve and integral
    Eight hypsometric curves were produced for the studied basin. According to the curves
    for sub-basins, sub-basins 1 and 2 had an under-curve area of above 50%, being relatively
    convex. This indicated the young age of the basin. Moreover, the convex form of the
    dimensionless curve indicated the prevailing of neo-tectonic activities over eroding ones.
    3.2. Calculating the asymmetry index of the basin.
    The asymmetry index was higher in basins 2, 5 and 6, and lower than 50 in 1, 3, 4, 7 and
    8, which points out their deviation. The T index indicated the semi-asymmetric form of
    the majority of sub-basins that fall into class 2 regarding their tectonic activities. The river
    gradient index was one of the significant indicators for differentiating between active and
    non-active tectonic areas. The mean stream length gradient index or SL for the basins
    varied from 482 for basin 2 to 71 for basin 6. The VF index showed that the bulk of the
    basin is within the active area; indicating that tectonic activities have not given the stream
    sufficient opportunity for erosion. The basin shape index for each case indicated that
    basins 2 and 7 are active and elongated, while the rest are inactive and fall into class 3.
    3.3. Relative evaluation of regional tectonic activates according to geomorphic
    indicators (IAT)
    In this study, eight morphotectonic indicators were calculated for each of the 8 basins,
    dividing them into 3 geomorphic levels. Then, the values for geomorphic index (S/n) were
    measured discretely for each basin; being classified into 4 levels, i.e. the index of relative
    active tectonics (IAT) of the study’s expanse. The classification for geomorphic
    indicators proposed by Hamdoni, Irigaray, Fernandez, Chancon & Keller (2008)
    classified these indicators based on the quantitative value into 4 classes. The class
    quantities of all indicators were combined, and their mean values were presented as the
    IAT index, indicating the tectonic activity. According to the results obtained from the
    IAT index, there is very strong tectonic activity in basin 2, with strong, moderate and
    weak tectonic activation witnessed in the remaining basins. The results of evaluation
    showed that the basins’ tectonic activities range from very strong to strong, moderate and weak.
    4.
    Conclusion
    Quantitative measurement allows geomorphologists to compare different landforms in a
    factual, rational manner, subsequently calculating morphologic indices. Regarding the
    hypsometric curve and integral for sub-basins 1 and 2, the under-curve area was above
    50%, indicating its young age. Also, the convexity of dimensionless curves indicated the
    prevalance of neo-tectonic activities over eroding ones. For sub-basins 3 to 8, the undercurve area was below 50%, resulting in a more concave hypsometric curve that indicated eroding activities in these sub-basins. Concavity in the dimensionless curve indicated the dominance of eroding activities over neo-tectonic ones.
    4.1. The asymmetry index of the drainage basin
    In basins 2, 5 and 6, this index was above 50, while for basins 1, 3, 4, 7 and 8, it was
    below 50. This indicated the deviation of basins. The topographic symmetry index
    indicated that the majority of basins are semi-symmetric, falling into class 2 regarding
    their tectonic activities. In the studied region, the SL index for the main waterways of 8
    sub-basins was measured. The mean value of the gradient index or SL for the basins
    varied from 482 for basin 2 to 71 for basin 6. According to the valley width to height
    index, the bulk of the basin is within the active region. This indicated that tectonic
    activities have not given the regional stream sufficient opportunity for erosion. The V
    ration index, called the valley morphology index, was obtained via comparing the
    transverse area of the actual valley to the area of a hypothetical semicircle with a radius
    equal to the valley depth. In sub-basin 7, it indicated the existence of a valley with larger
    width and less depth, the type which incurs higher erosion.
    The basin shape index indicated that basins 2 and 8 are active and elongated, while the
    rest are inactive and fall into class 3. The IAT index classified the tectonic activities of
    the region in the three classes of very strong, strong and moderate. According to this
    index, there is no basin with weak activities in the region. According to the segmentation
    map, the highest activity occurred in sub-basin 2, and the least in sub-basins 3, 4 and 7.
    The study and evaluation of different geomorphic indicators of the region show that it is
    young and active regarding neo-tectonic activities, yet this activity is not equal in all
    sectors. In sub-basin 2, young activities were the highest. This could be attributed to the
    stronger activity of the major and minor faults, resulting in the rise of the area.
    Keywords: Benarvan fault, Neo-tectonic evaluation, Morphological indicators
  • Hossein Asakereha, Ali Shahbaeekotenaeeb Page 109
    1.
    Introduction
    One of the special temperature states in which extreme amounts of minimum temperature are observed, is the cold wave. The extreme cold waves due to the severity and sudden occurrence have an important impact on the ecosystems and human societies. There is a probability of occurrence of cold waves throughout the year and in each season, it creates its own special problems and damages. Because of the low angle of sunshine and the cold weather, these waves are stronger in winter and threaten the life of all living creatures.
    They also play a decisive role in economic, environmental and developmental issues such
    as road construction, damping and bridge construction, and can cause damage in various
    sectors. The intensity and weakness of the cold waves depend on the complex synoptic
    and dynamics factors, some of which are less well-known and their analysis using a
    synoptic method can identify features such as the source, track, intensity and frequency
    of pressure systems and helps to recognize the fundamental factors and their characteristics and to increase our understanding of winter cold waves.
    2. Material and
    Methods
    The study area in this research includes the whole country of Iran. Iran is a rugged country with an elevation average of about 1250 meters. roughness plays an important role in Iran's temperature; therefore, the temperature decreases wherever height increases. Iran’s average maximum temperature is 18 degrees Celsius and the average minimum temperature is 11 degrees Celsius.
    In the present study, the effective patterns in creating winter cold waves in Iran were
    identified using environmental to circulation approach. In order to achieve the specified
    purpose in this study, two environmental and atmospheric databases were used.
    Environmental data included the minimum temperature in winter between 1960 and 2011.
    In this research, it has been attempted to be defined the cold Somehow so that the principle of its relativity is considered in different regions; accordingly and according to Alijani and Hooshyar (2008) and Massoudian (2013) researches, Two conditions for the
    identification of cold waves were defined in the country. On the basis of the first
    condition, days were considered as a day with a cold wave that standard Z score for the 10th percentile of minimum temperature data is less than or equal to -1/2. By defining
    this condition, only very low temperatures were taken into consideration for each of the
    7187 cells studied and the concept of relative coldness was considered for different
    regions of the country. The second condition is the continuity of the cold weather for at
    least 3 days; based on this condition, the systemic coldness from the local coldness (which
    is caused by environmental factors or overnight cooling) is separated. According to these
    conditions, cold days were identified on the ground and related synoptic systems were
    investigated in different layers of the atmosphere.
    3.
    Results And Discussion
    In the first pattern, about 45 percent of the country's surface was affected by the cold
    wave, and the average minimum temperature was -4.4 Celsius degrees. Based on surface
    temperature maps in the northwestern part of the country, temperatures below -20 ° C
    was observed. The main factor behind the formation of this pattern is the Azores high
    pressure system, which has led to cold weather penetration from northern Europe to Iran.
    Due to the formation of the second pattern, about 21 percent of the Iran’s surface was
    affected by the cold wave. The average minimum temperature in the country is -2.9
    Celsius degrees, which was the highest among other patterns. The lowest temperatures in this pattern were between -14 and -18 Celsius degrees that observed in the northwest, the central parts of the Alborz and northeast of the country.
    In the third pattern, the daily average of minimum temperature is -2.5 Celsius degrees,
    which is the lowest at the different patterns. In this pattern, 50 percent of the countrys
    surface was affected by the cold wave. In this pattern, cold weather penetrates the
    southern parts of the country and its impact was observed in many parts of the country.
    On the day the representative, the Siberian high-pressure system is located at high
    latitudes and in the central parts of Russia. The weakening of the Iceland low-pressure
    and the displacement Azores high-pressure towards the westerner parts, has strengthened the Siberian high-pressure and increased its impact.
    The minimum temperature average in the fourth pattern was -3.5 Celsius degrees and the cold air coverage in the country was 30 percent. Lowest temperature values were
    observed in northern parts of the provinces of East Azerbaijan and Ardabil. This pattern
    is somewhat similar to the first pattern, but contrary to the first pattern, there is a negative pressure anomaly in the northern regions of Europe and throughout Russia. The Siberian high pressure has shifted to the east and the European high pressure is located throughout the region, while in the first pattern, this high pressure was located in Western Europe.
    The minimum temperature average in the Fifth pattern was -3.4 Celsius degrees and the
    cold weather coverage in the country was 36 percent. In this pattern, the core of the
    Siberian high-pressure is located in west of Mongolia, and the Icelandic low-pressure was
    eastward movement and located in Scandinavia. This system has been located in large
    parts of northern Europe and central Russia as well as parts of the Atlantic in Western
    Europe. The expansion of this system and its displacement have caused more impact on
    Siberian high-pressure.
    4.
    Conclusion
    Performing synoptic analyzes on atmospheric patterns showed that all the pervasive cold
    waves in Iran were caused by the formation of massive high-pressure patterns in the
    country, parts of the Middle East and Asia and South-East Europe. The position of the
    two Siberian and Azores high-pressure systems has played a very important role in the
    transfer of cold air to the northern latitudes towards the country. The deployment of a
    polar low-pressure system in northern parts of Europe and Russia has led to the influx of
    cold air towards the southern regions. The formation of specific patterns of the
    intermediate layers of the atmosphere has had a significant effect on the creation and
    intensification of the winter cold waves. So that the extreme winter cold waves are formed when Blocking systems have been established in Eastern Europe and their eastern Trough has been located on Iran.
    Keywords: comprehensive Cold wave, cluster analysis, synoptic climatology, blocking system, Iran
  • Mosayeb Heshmatia, Mohammad Gheitourib, Morad Sheikhvaisic, Mahmood Arabkhedrid, Majid Hossinie Page 125
    1.
    Introduction
    Zagros forests (Quercus sp.) contribute to recharging groundwater, controlling air
    pollution, ecotourism, by products, livestock grazing, sustaining agriculture, soil
    conservation and flood control. Due to geological and topographical properties of Zagros
    area, however, these forests are more vulnerable to deforestation agents mainly drought
    driven die-off phenomenon. The effects of climate change are generally expected to
    reduce the growth and survival of forests, which not only predisposes them to being
    disturbed by insects and disease, but also increases the vulnerable ones to higher tree
    mortality. As a consequence of continued climate change, forest mortality has spread
    throughout Zagros areas inducing a severe environmental disaster. According to some
    research, several biotic and abiotic factors, such as extreme weather conditions, drought,
    storms, heat, and insect fluctuations, are responsible for oak reduction. Regarding rainfall
    deficit, soil moisture storage and reduction in evapotranspiration should be considered as
    the possible solutions through short term measures. Consequently, harvesting runoff by
    micro-catchment construction such as crescent -shaped bund (CSB) is a possible adapted
    measure in the semiarid regions for enhancement of soil moisture. In order to evaluate the effects of runoff harvesting on forest rehabilitation, the present research aimed to analyze the effects of CSB on soil soil moisture content.
    2. Material and
    Methods
    This study was conducted in Kalehzard site located in Kermanshah, west of Iran (UTM;
    38S682887E, 3748385N). The respective annual precipitation and temperature are 440
    mm and 15.2 ºC, indicating the semiarid region. The winter is so cold that the
    temperature drops below zero on average for 90 days during December, January and
    February. The summer is relatively hot and dry. A hill with a 15% slope and southeastern
    aspect was chosen as the experimental site to represent the dieback phenomenonin Zagros forests. The experiment was a randomized complete block design with four
    treatments and three replications. The experiment was conducted as a randomized
    complete block design with four treatments including crescent shaped bund with
    preservation (CSB), preservation treatment (PT), crescent shaped bund without
    preservation (CSB-P) and control treatment (CT). CSB was constructed to assist
    reduction in dieback rate and even re-vegetation of some dried forest trees through its
    effects on harvesting runoff. This technique is perpendicularly in the slope direction
    with the opening perpendicular to the flow of runoff, capturing runoff inside. The
    frequency of both dieback and healthy trees was recorded twice a year, therefore, the
    total number of trees was recorded before the construction of bunds within the plots
    using 100% inventory method. Soil quality, soil moisture and plant canopy were
    analyzed within treatments and repeated every year during the research period.
    3.
    Results And Discussion
    Results explored that the effects of CSB treatment on reduction of dieback rate and
    re-growing of some dried trees was 36.7 and 19 tree ha-1 respectively (totally 55.7 ha-1
    tree in the forest stand). Therefore, both the reduction of mortality rate and re-growing
    of dried trees are two main positive effects demonstrated by CSB measure. PT
    treatment has no effect on re-growing, while it contributes to the reduction of dieback
    severity (37.7 tree ha-1). Finally, CSB-P was found the lower level on dieback
    reduction was 6 tree ha-1, revealing the crucial importance of preservation for the
    protection of built bund. As a result, micro-catchment and preservation have a
    significant positive effect on forest restoration through soil moisture retention.
    Results
    also showed that the respective means SOC in the CSB, PT, CSP-P and CT
    treatments were 2.35, 2.40, 1.90 and 1.80 %, indicating no significant difference among
    them. However, the means significantly (p>0.05) increased in the CSB and P
    treatments over time. CSB significantly reduced bulk density from 1.46 (1st yr) to
    1.32 (3rd yr) enhancing soil moisture content. The crescent shaped bund was designed as the adaptive micro-catchment runoff harvesting system (MCRHS) and measured within
    treatments plots. This technique has a lower soil and embankment movement than
    earthy or stone dams which can be built perpendicularly in the flow of runoff. Besides,
    it is arranged in staggered rows along the natural contour of the land with the open end
    facing uphill. Consequently, these bunds slow down runoff enabling the harvested water
    to be used in an effective way. This is particularly useful in increasing the soil moisture,
    especially when precipitation is scarce.
    4.
    Conclusion
    It is concluded that CSB (first treatment) can be considered as the possible adaptation
    approach for combating Zagros forest mortality induced by drought stress and climate
    change. This technique is a possible measure for runoff harvesting and thereby
    enhancement of soil moisture during dry season. However, proper and holistic
    management of forests are needed to curtail forest dieback event. Furthermore, Zagros
    forest soil should be protected from disturbance factors in terms of tillage practice, machinery traffic, grazing, logging and charcoal extraction. In our experience, runoff
    harvesting through micro-catchment technique, forest preservation and sustaining SOC
    are crucial short term measures for combating forest mortality in Zagros regions.
    Keywords: Adaptation approaches, Crescent bund, Oak dieback, Soil moisture
  • Omid Mafakheria, Mohammad Salighehb, Bohlool Alijanic, Mehri Akbarid Page 143
    1.
    Introduction
    Since the spatial and temporal distribution of rainfall in Iran is influenced by the
    distribution of global circulation systems, the lowest change in its pattern is resulted in
    the severe weather abnormalities. Therefore, spatial and temporal abnormalities of
    rainfall, severe changes in rainfall intensity, and rainfall difference are the main
    characteristics of Iran's rainfall. Worthy studies have been carried out in relation to the
    temporal and spatial variations of rainfall, as a result, their conclusion showed that the
    number of precipitation is lower but the severity is higher. The purpose of this study
    was to investigate and identify changes in the number of rainy days, average daily
    precipitation, rainfall variation changes and the resulting hazards in the long-term
    statistical period.
    2. Material and
    Methods
    First, daily precipitation data of 53 synoptic stations with a common statistical period
    from 1984 to 2013 were received from the Meteorological Organization. Then, they
    were selected to determine the rainy day (precipitation at 0.1mm and above). From the
    viewpoint of precipitation duration, 7 classes were identified. 1 day precipitation,
    precipitation with two-day sequence, and precipitation with a sequence of 3 to 7 days of
    rainfall were extracted. Cluster analysis was used to identify climatic regions and their
    features. The final result was the division of the country into seven regions with the
    highest intra-group similarity and the most difference among groups in terms of the
    number of days. In order to identify hazards and heavy rainfall, the frequency of one
    day to seven days and more, to 3 parts of short term precipitation include 1 day
    precipitation, 2 days and 3 days, medium term (4 days and 5 days precipitation) and
    long-term (6 days and more) was divided. Then, in order to determine the changes in the
    daily rainfall of each area, first, the average daily rainfall of the short, medium and long
    run rainfall was calculated and the coefficient of variation of rainfall day and average
    daily precipitation for each of the areas was obtained. The final map was used in GIS
    using spatial analysis for zoning. In order to provide the time and spatial distribution
    pattern of precipitation in each area and to identify the severity of daily precipitation, the ratio of maximum daily rainfall to annual precipitation was calculated and analyzed.
    In order to compare rainfall variations in the first 15 years of the first 15 years, the
    coefficient of increasing or decreasing rainfall changes was calculated in two periods.
    3.
    Discussion
    In area 1 (south and south east of the country), the number of rainy days, the average
    rainfall of short-term days (precipitation of one to three days), and the medium-term
    (precipitation of four and five days) decreased. The average daily rainfall in this area
    was 17 days a year. In area two, the number of rainy days and the average amount of
    short-term and medium-term rainfall have been decreasing. The number of rainy days
    was 27 days a year with a mean precipitation of 3.1mm. In the third zone (Caspian
    coastlines), it was shown that the short-term rainy days are increasing, and the longterm
    and long-term periods of decline are decreasing. The number of overnight days in
    this area has been the highest (113 days) per year. In area 4, short and medium rainfall
    is increasing in terms of the number of days of precipitation. However, long-term
    precipitation (precipitation with 6 and 7 days and more) has been decreasing. The
    number of days in this area is 74 days (with an average rainfall of 4mm) per year. In
    zone 5, both short-term and medium-term rainfall showed a decrease in both trends,
    while the shortened rainfall is also higher in this area. The total number of days in the
    study period showed a decreasing trend. The annual rainfall in this area is 39 days (with
    an average rainfall of 2.3mm) per year. In area 6, the number of rainy days and the
    average daily rainfall (1-3 days) is increasing. Finally, in area 7, the number of
    overnight days (with a coefficient of 101) and the short run average had an increase.
    The medium-term and long-term rainfall have declined. The annual rainfall in this area
    was about 5mm in 66 days with an average rainfall.
    4.
    Conclusions
    1. Dry and semi-arid regions of Iran include areas 1, 2 and 5 (Bandar Lengeh, Konarak,
    Chabahar, Zahedan, Bandar Abbas, Bam, Zabol, Iranshahr, Kish, Abadan, Yazd, Tabas,
    Fasa, Bushehr, Birjand, Kerman, Kashan, Abadeh, Semnan, Isfahan, Ahvaz, Sabzevar,
    Qom, Shiraz and Torbat Heydarieh). The number of short-, medium-term precipitation
    days (precipitation with a 1-day, 2-day and 3-day sequence) and medium-term
    precipitation (precipitation i) has declined over the course of 30 years. Long-term
    precipitation (more than 5 days) has not occurred in these areas. The average daily
    rainfall in arid regions of Iran is 27 days a year. The average daily rainfall of both short
    and medium term has been decreasing. The average daily rainfall was 2.3mm per day.
    2. The northern coast of Iran was designated as area 3. The frequency of short-term
    barge days and the average rainfall are both incremental. An increasing trend indicated
    that rainfall has been severe. 9% has been added to the amount of daily precipitation.
    The daily rainfall in the region is 113 days per year and the average daily precipitation
    is 22.9mm.
    3. Mountainous area includes areas 4, area 6 and 7 (Ardebil, Gorgan, Parsabad, Khoy,
    Bojnourd, Tabriz, Quchan, Shahroud, Dashan Tepeh, Maraghea, Karaj, Qazvin,
    Shahrekord, Mashhad, Orumieh, Zanjan, Hamedan, Sanandaj, Yasouj, Ilam, Khorram Abad, Arak, Hamedan Nogheh, Kermanshah and Saqqez). In the statistical period of 30
    years in the mountainous areas, the number of days and average rainfall has decreased
    for the medium and long term, and has been increased by the number of short-term
    overnight days and short-term average rainfall. The number of rainy days in
    mountainous areas is 68 days per year and the average daily rainfall is 3.74mm.
    4. The ratio of maximum daily rainfall to annual rainfall in all areas is increasing. This
    indicates heavy rainfall and that rainfall in the region of Iran is rising. Most rainstorms
    occur within just a few days. Such anomalies in the regime of rainfall, long dryness,
    destruction of vegetation, followed by flood descendants and the destruction of water
    and soil resources and human facilities.
    Keywords: Rainfall hazards, Rainfall variations, Daily precipitation, Precipitation sequence, Showers
  • Negar Siabia, Seyed Hossein Sanaei Nejadb, Bijan Ghahramanc Page 163
    1.
    Introduction
    Precise estimates of rainfall in areas with complex geographical features in the field of
    climatology, agricultural meteorology and hydrology is very important. TRMM satellite
    is the first international effort to measure rainfall from space reliably (Smith, 2007).
    Another set of data that has become available in recent years is the output of numerical
    prediction models. Akter and Islam (2007) used MM5 model for weather prediction
    especially for rainfall in Bangladesh. They compared MM5 outputs with 3B42RT
    production of TRMM, rain gage and radar data and concluded that MM5 is reliable for
    rainfall prediction. Ochoa et al. (2014) compared 3B42 product of TRMM with
    simulated rainfall data by WRF model. Their results showed that TRMM data is more
    applicable for presenting spatial distribution of annual rainfall. In addition to the
    methods of statistical comparison, the similarity algorithm (Herzfeld & Merriam, 1990)
    was also used in this study. This algorithm compares a large number of data
    simultaneously, which can be in the form of maps or models output. In Iran, very few
    studies have compared the output of numerical prediction models with TRMM products
    of rainfall. The aim of this study was to evaluate and compare the rainfall data using
    similarity algorithm for different locations and time periods in order to fill a gap in the
    space-time data.
    2. Material and
    Methods
    The study area consisted of North Khorasan, Khorasan Razavi and South Khorasan
    provinces in North East of Iran, which is geographically located between the longitudes
    of 55 to 61 degrees and latitudes of 30 to 38 degrees. The climate of the area is arid and
    semi arid. Total area is approximately 313000 square kilometers. In this study, three
    types of data were used. Ground-based observations used from synoptic and rain-gauge
    stations of Meteorology Organization. The seventh series products of TRMM 3B42 sensor containing three hours TRMM rainfall data with a spatial resolution of 0.25
    degree were downloaded for free from the site of NASA. MM5 model outputs which
    were in the form of images with a spatial resolution of 0.5× 0.5 degrees for the period of
    2000-2010 were also obtained from NASA and NOAA .In this study, KED as a
    geostatistical method was used to interpolate rainfall. For running geostatistics
    algorithms, GS and ArcGIS software were used. Similarity algorithm was executed
    for each grid point map and the similarity values were derived. After standardization by
    calculating the similarity value for the entire study area, F network model for similar
    map was created. In similarity algorithm, closest values to zero indicate a good
    similarity between the input maps in a specific location and higher values indicate
    weaker similarity. Standardization algorithms, similarity and analytical software
    programming in MATLAB were performed for each grid point of the map.
    3.
    Results And Discussion
    RMSE values for MM5 model were higher in the warm months. The highest RMSE
    values were obtained in late spring and early summer. This result proved that in the
    summer, rainfall was predicted less accurately than in the cold months in winter. RMSE
    values for TRMM showed a reverse pattern with MM5 model output. Maximum
    amount of RMSE for TRMM was obtained in January with 14 mm per month. The
    reason for this may be because microwave energy scattering from frozen ice on the
    ground. The scattering from rain or frozen rain in the atmosphere is similar. Similarity
    values in the area were scattered with uniform distribution that represents the least
    significant inter-annual variation is cold seasons. For the warm seasons, in the south and
    north of the area, similarity values vary from 1 to 2. Results showed that inter-annual
    variations of rainfall in warm seasons and in central areas is high. One of the reasons for
    these results can be errors in the observed data.
    By examining the time series of TRMM images using similarity algorithm, we found
    that in the cold season, the south zone of the study area had similarity values 0.05 to 0.1
    with a uniform distribution of values. However, higher similarity values were obtained
    for the northern and central areas where the distribution of similarity values was not
    uniform.
    Due to these facts, it can be concluded that rainfall production of TRMM data was
    relatively good in the cold season in south and relatively week in north and central parts
    of the region. In the warm season the least amount of similarity could be seen in the
    northeast part of the study area. But generally, TRMM estimated rainfall fairly in the
    warm season.
    4.
    Conclusion
    The validation results of MM5 model rainfall and TRMM monthly rainfall images
    showed that the model predicted rainfall amounts in the cold months better than in the
    warm months. However unlike the MM5 model, remote sensing images had the highest
    error in cold months. The reason was the presence of snow and ice on the ground in the
    cold months of winter. Considering inter-annual and seasonal changes, it became clear
    that there is much difference between inter-annual remote sensing image changes and the actual amounts of rainfall (KED). Nevertheless the model inter-annual changes were
    consistent with real data. Inter-annual changes of the model and the station data (KED)
    were higher in cold season.
    KED methods also retained spatial variability of rainfall as well as remote sensing data
    and model output. The estimates, especially above 1500 meters in the central regions,
    had low precision in the products. The results showed that in the absence of adequate
    rain gages in the region, MM5 output model and TRMM data could be used to fill the
    gaps.
    Keywords: MM5, Precipitation, Similarity algorithm, TRMM
  • Abdolreza Kashkia Page 181
    1.
    Introduction
    Today, climate change problem is considered as one of the most common scientific
    subject, even as social and political issues, in fact it is not novelty issue. Principally,
    because the change and movement are one of the component in macro scale climatic
    systems, discovering the legitimacy of these systems, which mainly is cyclic, it is can be
    consider as a tool which can help to predict future behavior of the system. The polar
    vortex (PV) is defined as a large-scale upper-level cyclonic circulation in the middle
    and upper troposphere which is centered on the polar region. Measurement undertaken,
    observational investigation and modeling indicate the oscillation cycles of polar vortex.
    There are two effective mechanisms for oscillation cycles of polar vortex that could be
    divided into two categories: internal and external. The internal mechanism is included
    investigation of oscillation cycles of polar vortex by applying thermal and wavy forcing,
    which is independent of time and leads to identify the effect of the stratosphere on the
    troposphere. External mechanism is included investigation of oscillation cycles of polar
    vortex by applying thermal and wavy forcing, which is depends on time and leads to
    identify the effect of the troposphere on the stratosphere. Trend changes on the macro
    scale climatic system, such as polar vortex has a significant role on climate change of
    the surface. Variability in the atmospheric circulation at the hemispheric-scale can have
    a direct impact on variations in the surface environmental parameters, such as
    temperature, precipitation, and pollutant transport. One indicator of the behavior of the
    hemispheric-scale circulation is the polar vortex. The polar vortex can be used for study
    the holistic hemispheric-scale sub-tropical circulation because it represents the
    characteristics of long-wave, upper-level ridge-trough configuration around the entire
    (northern or southern) hemisphere at a given point in time. The PV is defined as the
    large-scale upper-level cyclonic circulation in the middle and upper troposphere
    centered on the polar region. The most fundamental question addressed in this research
    is whether the northern hemisphere polar vortex (NHPV) exhibits long-term trends in
    area over the 1948-2007 periods. Therefore, the first part of this study answers the
    question: How can we characterize the long-term trend of the area of the NHPV? It is
    hypothesized that the global warming signal would be associated with a reduction in
    area in the NHPV over time as the cold pool of air over the poles shrinks.
    2. Material and
    Methods
    In this research, daily mean data of 500 hPa geopotential height were used from the
    National Center for Environmental Prediction & National Center of Atmospheric
    Research (NCEP/NCAR) during the period of 1948 to 2007. Their spatial resolution is
    2/5 * 2/5 degree with 36 * 144 pixels. The 500 hPa geopotential height (i.e., constant
    pressure surface) was selected for analysis for several reasons. First, since the 500 hPa
    level is in the middle of the atmosphere, it represents characteristics of both the lower
    and upper atmosphere. Also, most steering of mid-latitude systems occurs at the 500
    hPa level and geostrophic flow occurs at this level as well. A specific isohypse(contour)
    is selected to represent the NHPV for each month in 500 hpa level (table 1).
    Monthly polar vortex area is calculated with Grads software. This research utilizes a
    statistical approach to determine the trend in the northern hemisphere (NH) polar
    vortex. For comparison of area means, used from Paired-Samples T Test and for the
    detection of polar vortex area trend used from Kendall's tau trend test in SPSS software.
    Paired-Samples T Test is one of the statistical parametric tests to compare the mean and
    variance of the two dependent groups in a region.
    3.
    Results And Discussion
    By doing the Kendall tau test in SPSS, it was determined a reduction in the polar vortex
    area in all months. Polar vortex area has a decreasing trend during May, June, July,
    August, September and March which is significant at 0.01 level.
    The biggest reduction trend is related to August and lowest to December. The
    Results
    show that the polar vortex during the whole period is declining, but this decline was
    higher during summer months. The most of decline in the polar vortex area is observed
    in August that the rate of about 93,000 square kilometers per year. The decline rate has
    accelerated in the second half of period. Generally, the decline of polar vortex area
    caused by macro-scale climate change and planetary scale, That certainly global
    warming and consequently advancement of subtropical high pressure will be one of the
    components. The results of Paired-Samples Test showed that the mean difference of
    polar vortex area is negative for all months and this amount represents a reduction in
    polar vortex area during thirty years of second period compared to the first period.
    4.
    Conclusion
    The change in configuration of polar vortex (trough and ridge) and transformation from
    zonal to meridional as a result of reducing of meridional pressure gradient caused
    regional climatic anomalies such as the change in the type and amount of precipitation
    and temperature. Generally, the decline of polar vortex area caused by macro-scale climate change and planetary Scale, that certainly global warming and consequently
    advancement of subtropical high pressure will be one of the effective components.
    Keywords: Polar Vortex, Trend Analysis, Climate Change, Northern Hemisphere