فهرست مطالب

پژوهش های جغرافیای طبیعی - پیاپی 115 (بهار 1400)

فصلنامه پژوهش های جغرافیای طبیعی
پیاپی 115 (بهار 1400)

  • تاریخ انتشار: 1400/03/30
  • تعداد عناوین: 8
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  • رضا خوش رفتار* صفحات 1-19

    ژیومورفولوژیست‏ها، خواسته یا ناخواسته، عملا با مسایل فلسفی و روش‏شناسی سروکار دارند؛ اما ممکن است همیشه، به‏شکلی صریح و روشن، به آن‏ها نپردازند. اگرچه شماری از نویسندگان در مقالات و کتاب‏ها به مسایل فلسفی و روش‏شناسی پرداخته‏اند، تا زمانی که به‏صورت فراگیر در ژیومورفولوژی مطرح نشود، اهمیت و همچنین مشکلات آن مشخص نخواهد نشد. همان‏طورکه ژیومورفولوژی در ابتدا بر اساس کارهای میدانی‏ که مبنای فلسفه طبیعی بود‏ شکل گرفت و یک بار دیگر ژیومورفولوژیست ها باید به دیدگاه های فلسفی، اهمیت بیشتری بدهند.، بار دیگر باید به دیدگاه‏های فلسفی اهمیت بیشتری دهد.  فقط با نگاه عمیق‏تر به نگرش‏ها و دیدگاه‏ها درباره طبیعت، چشم‏اندازها، و لندفرم‏هاست که روش‏شناسی و فلسفه علم ژیومورفولوژی توسعه می‏یابد. بدون آگاهی از هستی‏ و معرفت‏شناسی ژیومورفولوژی، این علم بی‏معنی خواهد بود. اگرچه از دیدگاه‏های فلسفی مانند تجربه‏گرایی در تجزیه‏و‏تحلیل لندفرم‏ها استفاده شده است، به کثرت‏گرایی در ژیومورفولوژی باید توجه بیشتری شود. در این مقاله، با استفاده از منابع معتبر متعدد، اهمیت توجه به فلسفه علم ژیومورفولوژی به روش تحلیلی نقد و بررسی شده است. چون یکی از چالش‏های آینده علم ژیومورفولوژی پرداختن بیشتر به استدلال‏های فلسفی و اندیشمندانه است، ارتباط متقابل بین فلاسفه علم و ژیومورفولوژیست‏ها می‏تواند آغاز این راه باشد.

    کلیدواژگان: تبیین علمی، ژئومورفولوژی، لندفرم‏ ها، هستی، معرفت‏ شناسی
  • سمیه سلطانی گردفرامرزی*، مریم مروتی صفحات 21-36

    پدیده گرد و غبار یکی از مخاطرات اقلیمی و زیست‏ محیطی مهم در مناطق خشک و نیمه ‏خشک جهان است. این مطالعه برای بررسی برخی از مهم‏ترین ویژگی‏های گرد و غبار اتمسفری شهر یزد، به‏عنوان یکی از شهرهای مهم مناطق خشک کشور ایران، انجام شده است. از زمستان 1397 تا تابستان 1398 به‏ صورت فصلی در 30 نقطه از شهر یزد با استفاده از تله رسوب‏ گیر از گرد و غبار اتمسفری نمونه‏برداری شد. همچنین، برای مقایسه نتایج گرد و غبار اتمسفری با خاک منطقه، 30 نمونه مختلف خاک سطحی از عمق 0-10 سانتی‏متری از مناطق نزدیک نقاط نمونه‏برداری گرد و غبار تهیه شد. سپس، برخی ویژگی‏های شیمیایی و فیزیکی از جمله بافت، pH، هدایت الکتریکی، غلظت نیترات، بی‏کربنات، فسفر، گوگرد، سدیم، پتاسیم، منیزیم، و کلر در نمونه ‏های گرد و غبار و خاک، همچنین نسبت غنی‏ شدگی عناصر در گرد و غبار تعیین شد. کانی‏ شناسی ذرات گرد و غبار نیز با آنالیز XRD مشخص شد. کلاس بافت خاک در هر چهار فصل مورد بررسی سیلت لوم محاسبه شد. نتایج نشان داد عناصر کلر و گوگرد در گرد و غبار نسبت به خاک سطحی به ‏طور قابل توجهی غنی شده‏ اند. کوارتز، کلسیت، و آلبیت کانی‏های اصلی و کلریت، ایلیت، مسکویت، و دولومیت به‏ عنوان کانی‏های فرعی گرد و غبار تعیین شد. با توجه به نتایج آنالیز XRD و اثبات حضور کانی کلسیت و آلبیت به ‏عنوان کانی‏های اصلی و وجود کانی کلریت به ‏عنوان کانی فرعی در این منطقه، همچنین با توجه به همبستگی بالا و مثبت یون‏های کلر، نیترات، پتاسیم، و سدیم با شوری در گرد و غبار وجود ترکیبات مختلف این املاح خصوصا ترکیبات کلرید سدیم و گچ در گرد و غبار منطقه مطالعاتی پیش‏ بینی می‏شود. بر اساس شباهت بین کانی‏شناسی نمونه‏ های گرد و غبار در منطقه با کانی‏شناسی خاک منطقه، احتمالا می‏توان یکی از منابع گرد و غبار منطقه را بیابان‏های اطراف شهر یزد دانست.

    کلیدواژگان: اندازه ذرات، خصوصیات شیمیایی، کانی‏شناسی، منشا گرد و غبار، نسبت غنی‏ شدگی، شهر یزد، ایران
  • مهری اکبری، وحیده صیاد* صفحات 37-74

    مطالعات تغییر اقلیم به دو گروه مدل‏سازی تغییر اقلیم و پیامدهای تغییر اقلیم تقسیم می‏شود که در این پژوهش به مطالعه گروه دوم تحقیقات پرداخته شده است. بنابراین، در مرحله اول موضوعات به چند دسته تقسیم شد که شامل اثر تغییر اقلیم بر وقوع مخاطرات محیطی، منابع آب، اقتصادی و کشاورزی است و همچنین اثر آن بر پیامدهای اجتماعی و سکونتگاهی که تاکنون در ایران انجام ‏شده است و نهایتا تحلیل این موضوعات. روش به‏کارگرفته‏شده در این مطالعه مطالعات کتابخانه‏ای و جست‏وجو در پایگاه‏های استنادی علمی مگیران، SID، و ScienceDirect بوده است. بر اساس نتایج این پژوهش، مرور منابع نشان داد، به نظر بیشتر پژوهشگران، مهم‏ترین پیامد پدیده تغییر اقلیم در ایران افزایش فرین‏های جوی بوده که به‏طور کلی یا بازه زمانی- فضایی الگوهای آب‏وهوایی تغییر کرده است یا رخداد آن‏ها بیشتر یا کمتر از میانگین بوده است. اما بر اساس نتایج مطالعات مورد بررسی، پدیده‏های حدی مانند خشک‏سالی بیش از سایر پدیده‏ها تحت تاثیر تغییر اقلیم قرار گرفته‏اند. همچنین، تحقیقات نشان دادند که در ایران، به‏عنوان کشوری در حال توسعه، در مقایسه با اقتصادهای قدرتمند، تغییر اقلیم بیشتر به بروز مسایل اجتماعی و اقتصادی منجر شده است.

    کلیدواژگان: اجتماعی، اقتصادی، ایران، تغییر اقلیم، مخاطرات، منابع آب
  • آذر زرین*، عباسعلی داداشی رودباری صفحات 75-90

    هدف از این پژوهش پیش‏نگری دمای ایران بر اساس رویکرد همادی چندمدلی (MME) با کاربست مدل‏های CMIP6 است. برون‏داد پنج مدل برای دوره تاریخی (1995-2014) و آینده نزدیک (2012-2040) تحت دو سناریوی بدبینانه (SSP3-7.0) و خیلی بدبینانه (SSP5-8.5) به‏کار گرفته شد. برای درستی‏سنجی مدل‏ها از سنجه‏های آماری MBE و NRMSE و داده‏های دمای روزانه 120 ایستگاه همدید استفاده شد. از روش‏های تغییر عامل دلتا (DCF) و میانگین وزنی مستقل (IWM) به‏ترتیب برای تصحیح اریبی و ایجاد یک مدل همادی استفاده شد. برای آشکارسازی تنش‏های گرمایی از شاخص طول مدت گرما (WSDI) استفاده شد. نتایج نشان داد که تصحیح اریبی و همادی‏کردن مدل‏ها با روش IWM پیش‏نگری دمای سالانه را به‏ویژه در مناطق خشک و نیمه‏خشک نسبت به مناطق مرطوب شمالی بهبود می‏بخشد. نتایج کلی نشان داد که بر اساس سناریوهای SSP3-7.0 و SS5-8.5، میانگین دمای سالانه کشور به‏ترتیب 13/1 و 26/1 درجه سلسیوس افزایش خواهد یافت. کمینه بی‏هنجاری در جنوب شرق و بیشینه آن در مناطق شمال غربی و مرکزی ایران اتفاق می‏افتد. شاخص طول مدت گرما نیز بی‏هنجاری مثبت‏ را برای آینده نشان می‏دهد. بر اساس سناریوی SSP5-8.5، بیشینه این شاخص در سواحل جنوبی ایران بی‏هنجاری مثبت 5/74 روز را نشان می‏دهد.

    کلیدواژگان: ایران، پیش ‏نگری دما، شاخص WSDI، مدل ‏های CMIP6، مدل همادی
  • حسین عساکره*، سید ابوالفضل مسعودیان، فاطمه ترکارانی صفحات 91-107

    طی سده گذشته، اقلیم به گونه‏ های مختلفی تغییر یافته است. این روند تغییرات احتمالا برای آینده ادامه خواهد داشت. یکی‏از جلوه ‏های تغییر اقلیم در وردایی رفتار دهه ‏ای بارش قابل ردیابی است. به‏منظور ردیابی وردایی بارش ایران طی چهار دهه اخیر (1355-1394) و تفکیک تغییرپذیری متاثر از مختصات (موقعیت) جغرافیایی (طول جغرافیایی و عرض جغرافیایی) و توپوگرافی (ارتفاع، جهت، و میزان شیب دامنه‏ ها)، به ‏عنوان عوامل درونی موثر بر بارش، از الگوی رگرسیون خطی چندمتغیره استفاده شد. بدین ترتیب، بارش متاثر از مختصات جغرافیایی- عوامل توپوگرافیک برای هر دهه از میانگین بارش دهه‏ ای تفکیک شد و الگوی مکانی بارش حاصل از عوامل بیرونی اقلیم بارشی به‏ دست آمد. بنابراین، تغییرات دهه به دهه بارش در ارتباط با عوامل بیرونی مورد مداقه قرار گرفت. نتایج نشان داد طی چهار دهه اخیر تاثیر عوامل بیرونی موثر بر بارندگی ایران موجب کاهش پهنه‏ های بارشی شده‏ اند؛ به‏ طوری‏که از اولین دهه مورد بررسی (1355-1364) به سمت دهه انتهایی (1385-1394) سهم عوامل بیرونی در وردایی بارش افزون‏تر شده‏ است. بعد از دهه دوم تاثیر عوامل بیرونی حتی نسبت به میانگین کل افزایش داشته‏ است؛ به ‏طوری‏که در دهه اول 4/54 درصد و در دهه آخر نزدیک به 60 درصد از گستره کشور با وردایی بارش حاصل از عوامل بیرونی مواجه بوده ‏است.

    کلیدواژگان: ایران، بارش، تغییر اقلیم، تغییرپذیری دهه ‏ای، وردایی بارش
  • محمدصادق کیخسروی کیانی*، سید ابوالفضل مسعودیان صفحات 109-121

    هدف از پژوهش کنونی واکاوی آب‏ و هواشناسی انباشت و گدازش پوشش برف در ایران با بهره ‏گیری از داده‏ های سنجنده مودیس است. برای این منظور، داده‏ های روزانه نسخه ششم پوشش برف سنجنده مودیس برای بازه زمانی 1/7/1380 تا 31/6/1397 در تفکیک مکانی 500×500 متر دریافت شد. در گام بعدی داده ‏ها به تفکیک هر سال آبی پردازش و فرایند محاسبه زمان‏بندی انباشت و گدازش روزهای برف‏پوشان انجام پذیرفت. پردازش‏ها نشان می‏دهد آغاز فصل انباشت برف از روی بلندی‏های البرز و بلندی‏های شمال ‏غرب کشور (رشته ‏کوه‏های سبلان) از اوایل مهرماه آغاز می‏شود و به‏تدریج با سپری‏ شدن فصل پاییز به ارتفاعات پایین‏تر گسترش می‏یابد. فصل انباشت برف بر روی رشته‏ کوه‏های زاگرس از حدود دهه اول آبان‏ماه از ارتفاعات حدود 4000 متر آغاز می‏شود و به ‏تدریج تا دهه اول آذرماه به ارتفاعات پایین‏تر (حدود 2200 متر) نیز کشیده می‏شود. طی ماه‏های آغاز انباشت برف در ایران، که دربردارنده ماه‏های مهر تا آذر است، ارتفاع برف‏مرز با آهنگ متوسط 54 متر در روز به پایین حرکت می‏کند؛ این در حالی است که طی ماه‏هایی که فرایند گدازش برف در آن رخ می‏دهد، یعنی ماه‏های دی تا شهریور، ارتفاع برف‏مرز با آهنگ متوسط 15 متر در روز به ارتفاعات بالاتر مهاجرت می‏کند.

    کلیدواژگان: ایران، انباشت و گدازش پوشش برف، برف‏مرز، سنجنده مودیس
  • محمد مهدی حسین زاده*، نیلوفر برخورداری صفحات 123-140

    رودخانه ‏ها سیستمی پویا بوده و برای رسیدن به تعادل بستر در مسیر خود برداشت، حمل، و رسوب‏ گذاری می‏کنند. به همین دلیل، مشخصه‏ های مورفولوژیک آن‏ها به ‏طور پیوسته در طی زمان تغییر می‏کند. در این پژوهش از روش پهنه ‏بندی آسیب‏ پذیری فرسایش کناره برای بررسی عوامل موثر (شیب کناره، الگوی پیچان رودی، شیب طولی رودخانه، فرسایش خاک، پوشش گیاهی، فعالیت‏های انسانی، و تنش برشی نزدیک کرانه) در ناپایداری و فرسایش کناری رودخانه هفت‏ چشمه در روستای رزجرد از توابع استان قزوین بخش رودبار الموت (معلم کلایه) و به طول تقریبی 11 کیلومتر استفاده شده است. با استفاده از نقشه ‏های توپوگرافی، تصاویر گوگل ارث، و بازدیدهای میدانی، پارامترهای هر بازه بررسی شد و سپس پهنه‏ بندی رودخانه از نظر مخاطره ‏آمیزبودن آن به پنج منطقه خیلی زیاد، زیاد، متوسط، کم، و خیلی کم تقسیم شد. نتایج نشان داد بیشتر بازه‏ ها در رودخانه هفت‏ چشمه از نظر حساسیت به فرسایش در وضعیت متوسط قرار دارند. اما در بازه ‏های 8 و 9 به دلیل فعالیت انسانی زیاد در حریم رودخانه در طبقه متوسط تا زیاد از نظر مخاطره قرار گرفته‏ اند. همچنین، در همه بازه ‏ها به ‏جز بازه 10 به‏دلیل حساسیت مواد کناره نسبت به فرسایش در طبقه متوسط تا زیاد قرار گرفته‏ اند.

    کلیدواژگان: آسیب‏ پذیری کانال، پهنه ‏بندی، رودخانه هفت‏ چشمه، فرسایش کناره ‏ای، قزوین
  • علیرضا کربلایی درئی*، زهرا حجازی زاده، سید ابوالفضل مسعودیان صفحات 141-155

    هدف از پژوهش حاضر واکاوی رفتار زمانی- مکانی سپیدایی روشن در ایران است. سنجنده مودیس سپیدایی تیره را برای تابش مستقیم و سپیدایی روشن برای تابش پراکنده همسان‏گرد در ظهر محلی ارایه می‏دهد. برای این منظور، داده‏ های ترکیبی سپیدایی سنجنده مودیس تررا- آکوا (MCD43A3v006) برای بازه زمانی 1378-1398 به ‏صورت روزانه و در تفکیک مکانی 500×500 متر به‏کار گرفته شد. تغییرات زمانی- مکانی مقادیر سپیدایی روشن با استفاده از تحلیل مولفه اصلی واکاوی شد. نتایج نشان داد سه مولفه اصلی قادر به تبیین 7/97 درصد از پراش داده ‏هاست. واکاوی مکانی سپیدایی روشن حاکی از آن است که سپیدایی ‏های بالاتر از میانگین در نواحی مرتفع و کوهستانی ایران، همچون رشته‏ کوه‏های زاگرس و البرز، ارتفاعات شمال غرب کشور مانند قله ‏های سبلان و سهند وجود دارد که در ارتباط با پوشش برفی است. بنابراین، مولفه اول پوشش برفی نام‏گذاری شد. در مولفه دوم سپیدایی در سه فصل بهار، تابستان، و پاییز برابر است. واکاوی مکانی مولفه دوم نشان داد سپیدایی‏های بالاتر از میانگین در ارتباط با پوشش نمکی است. بنابراین، مولفه دوم پوشش نمکی نام‏گذاری شد. واکاوی تغییرات زمانی سپیدایی در مولفه سوم حاکی از آن است که سپیدایی‏های بالاتر از میانگین در برف‏ خوان ‏هاست. درنتیجه، مولفه سوم برف‏خوان نام‏گذاری شد.

    کلیدواژگان: پوشش برفی، تحلیل مولفه اصلی، سپیدایی روشن، مودیس
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  • R. Khoshraftar * Pages 1-19

    Geomorphologists and Overlooking of Philosophy of Science in Geomorphology1-IntroductionIt is natural that a thoughtful man will attempt to understand the world and himself as part of it. Knowing about the subject under study is a prelude to each science. In numerous books, geomorphology is considered to be composed of three words of Greek origin, Geo (earth), Morphe (form) and Logos (identification) (Gutidrrez, 2005: 3; Thorn, 1988: 24; Chorley et al, 1996: 9). In the definition of the International Association of Geomorphologists (IAG), it is the interdisciplinary and systematic study of landforms, their perspectives, and surface processes that create and modify complications (www.Geomorph.org, 2013).Men has always raised questions for understanding and explaining how these reliefs are shaped and how these reliefs can be effective in their lives. Examples of commonly asked questions in geomorphology are:- Why are alluvial fans formed on the foothills?- Why are most caves formed in limestone?- Why are coastal cliffs retreating?To explain the why of landforms, how they are formed should be explained. For Newton(1643-1727), the scientist should look at how, not why. Why questions can be answered with complex and irresponsible speculation and how questions can be answered with experiment (Capaldi, 2011: 232).Although Whalley (1987: 86), believes that what questions, and the how of function and development of landscapes and landforms are dealt with in new geomorphological research, from the point of view of Yatsu, geomorphologists have tried to find answers to what, where and when questions and rarely seek answers to how questions (Gregory, 2010: 32). The purpose of this paper is to examine the role of scientific explanation in geomorphology and review and discuss the causes of insufficient attention of geomorphologists to philosophical issues in geomorphology and its implications..2-Material and MethodsConsidering the theoretical nature of the discussion regarding the ontology and philosophy of geomorphology, the research method in this article is analytical-descriptive. Therefore, several sources in this field, mainly in English, were developed and reviewed over a long period of time. Because the lack of proper explanation of the philosophy of a science, after a while, leads to the mass production of largely repeated fruitless works and tendency to adjacent sciences, the importance of explanation in geomorphology was first discussed and then the reasons for the neglect or insufficient attention of geomorphologists to different philosophical attitudes and theoretical frameworks in geomorphology have been criticized. In the end, due to the importance of addressing philosophical issues, the necessity of more attention of geomorphologists to the philosophy of geomorphology was analyzed and solutions were presented.3-Results and Discussions3-1. Is geomorphology a science?The definition of science can also be different depending on which school or philosophical perspective is to be considered. Baker considers science as a deliberate and observational process for understanding and knowledge that helps man understand the truth (Baker, 1996: 59). Finally, the answer to the question of whether geomorphology is a science or not is a personal choice. In a scientific approach, geomorphic systems are considered to be physical systems that have had historical changes. This view shows the importance of general physical theories and geo-historical theories about the evolution of a particular perspective (Rhoads and Thorn, 1993). Apart from the philosophical views or personal divisions, the reasons for geomorphology to be science are:1. Geomorphology seeks to explain landforms and processes.(e.g. the explanation of the events leading to the formation of alluvial cones).2. Geomorphology, based on causality, tries to place landforms and processes under general rules (generalization).(e.g. the explanation of the formation of alluvial terraces in relation to the slope law).3. Geomorphologists, like other experts in the field of empirical sciences, are always outside the scope of their research in the study of the subject.4. The geomorphologist's main tool for gaining knowledge is observation, measurement and experiment.5. With advances in science, including geomorphology, more knowledge will be obtained about complex problems in geomorphology in the future.3-2. Is there a connection between geomorphology and philosophy?Investigating landscapes is the main subject of geomorphology science (Harrison, 1999), and the necessary condition for this task is to collect data on ground forms and operating processes in accordance with ideas and hypotheses (Gregory, 2010: 29). Although the subject examined in geomorphology, i.e. the study of the evolution of landforms over time, fully reflects the philosophy and philosophical foundations of the field of geosciences (Rhoads and Thorn, 1994), and time was even one of the tripartite components of relief in the Davies paradigm, but "traditionally, geomorphologists refrain from discussing the philosophical foundations of geomorphology" (Harrison and Dunham, 1998). There are three reasons why geomorphologists are suspect of the role of theory in geomorphology:A. Differences in scientific viewpoints, goals and methodology of those who call themselves geomorphologists (Rhoads and Thorn, 1993). .B. Many geomorphologists consider their main task as field work and observation (Rhoads and Thorn, 1993) and agree with this view that the fieldwork and the relationships established between landforms during fieldwork are the geomorphologist's final work (Slaymaker, 2009). C. Extensive misinterpretation of the theory (a construction) against computing (communication device). Geomorphologists should not deceive themselves that the theory is not related to geomorphology, it is restricted to certain sciences, and has a computational aspect (Rhoads and Thorn, 1993). ConclusionsIf geomorphology aims to find a solid and supreme position among other sciences, geomorphologists must focus more on the philosophy and methodology of their discipline. The emphasis on explaining or recognizing how landforms and processes put geomorphology among empirical sciences. According to Rhoads (1999), physical geographers, and in particular geomorphologists, have begun to address philosophical issues. The interconnection between philosophers of science and geomorphologists can be the beginning of this work.With the attraction of geomorphology among geosciences (geology and geography), environmental sciences and engineering and that people with different backgrounds want to introduce themselves as geomorphologists, a geomorphologist should have a "geomorphologic" view: i.e. a mixture of intuition, impudence in theorizing, and liberation from everyday life, but dependent on the experience and the physical reality that is created through theories. The first step in this way is to focus on the basic sciences, in particular, physics and its combination with the spatial analysis of landforms.

    Keywords: Ontology, Epistemology, landforms, Explanation
  • Somayeh Soltani-Gerdefaramarzi *, Maryam Morovati Pages 21-36
    Introduction

    One of the most important phenomena in arid and semi-arid regions of the world is dust, which is one of the most important environmental issues in these areas. Low rainfall in these areas, have somewhat reduced water erosion, while the lack of vegetation and other factors contributing to soil erosion has provided the ground for the development of wind erosion and the occurrence of dust storms (Ali Sufi and Shahriari, 1399). The integration of these sources of atmospheric particle production with dust from the soil increases the amount of organic matter and heavy elements in the subsided dust in dry ecosystems (Jafari and Khademi, 2017). Rashki et al. (2013) showed that silica, calcium, aluminum, sodium, magnesium and iron oxide compounds are the most important oxide compounds and quartz, calcite, muscovite and plagioclase minerals are the most abundant minerals in Sistan dust particles. Ali Sufi and Shahriari (2020) examined some chemical properties and the amount of some nutrients along with dust in Sistan plain. Calcium and phosphorus were the most abundant nutrients in the region, with phosphorus and sodium being the highest and lowest enrichment ratios, respectively. Salahi and Behrozi (2020) in the Dezful region of Khuzestan province, Iran showed that among the soluble elements in dust, calcium, potassium, sodium and magnesium had the highest concentration and the tracing of the dust showed that the alluvial sediments of Tigris and Euphrates in Iraq has been the main source of dust in Dezful. Over the past few years, the city of Yazd has witnessed many severe dusts, and it is known that the discovery of the source and other characteristics of these particles has helped to better combat this phenomenon or reduce its effects and its amount. This is despite the fact that no community studies have been conducted on these features in the city of Yazd. Understanding how particles are distributed and their chemical dust and composition to determine the physical / chemical properties, resources and mechanisms of formation and behavior, as well as determining strategies to control it is useful and valuable. Therefore, this study was performed to study the chemical and physical properties of dust during different seasons and to determine the possible source of particles and dust.

    Materials and methods

    The present study was conducted in Yazd city, the most populous city and center of Yazd province with an area of 131600 Km2. In order to sample dust and surface soil, 30 sampling sites were randomly selected in the study area to provide adequate coverage throughout the area. For sampling of atmospheric dust, from Marble Dust Collector which is made of a plastic tray with several rows of marbles (at least 2 rows) with a tray diameter of 31.5 cm and a height of 5 cm and a diameter of 1.6 cm glass marbles were used. Sampling of atmospheric dust was carried out in four seasons of autumn and winter of 2018, spring and summer of 2019 in Yazd city at a height of three meters above the ground (roofs of one-story houses). Surface soil sampling was performed at a depth of 0 to 10 cm once during dust sampling and close to dust sampling points. The particle size distribution of dust samples was determined. Then there are some chemical and physical properties such as texture, pH, electrical conductivity, nitrate, bicarbonate, the concentration of P, S, Na, K, Mg and Cl were determined in dust and soil samples, as well as the enrichment ratio of nutrients in the dust. The mineralogy of dust particles was also determined by XRD analysis. The data obtained from the analysis of dust and surface soil samples were analyzed using SPSS 16 software. A comparison of the mean of the studied parameters and the significance of their differences was performed using Duncan's test at the level of 5%. Also, spatial distribution maps of the parameters studied in the study were plotted using the inverse distance weighting method (IDW) in Arc GIS 10.1 software.

    Results and discussionIn

    all seasons, silt particles (2 to 50 µm) make up the largest percentage of dust particles. Sand particles (more than 50 µm) make up the largest part of the particles after silt, and clay particles (less than 2 µm) have the lowest frequency of dust in the study area. According to the results, the pH of dust samples has changed from 7.10 to 9.74 with an average of 7.83, which compared to the results of soil samples fewer were found in all seasons. However, the minimum amount of pH was found in winter. Many researchers attribute the decrease in pH in cold seasons to a decrease in temperature and an increase in heating devices and fossil fuels, which causes CO2 and SO2 emissions to be released into the environment, thereby reducing pH (Jafari and Khademi, 2017). The average salinity in dust samples is 4412.93, which is less than the average salinity of the soil samples (minimum, maximum and average salinity of the soil 1990, 18060 and 6852.94 µS/cm respectively) while HCO3 (with an average of 23729.47 mg / kg) and K (with an average of 18972.82 mg / kg) were found in dust samples higher than surface soil samples (with an average of 1239.39 and 16633.06 mg / kg, respectively). HCO3 has the highest amount in summer (2770 mg / kg) and the lowest in spring (1720 mg / kg). NO3 has maximum (4017 mg / kg) and minimum (10.5 mg / kg), respectively, in spring and autumn. Except for the autumn season, nitrate in all seasons of sampling was higher than the amount in surface soil (231.27 mg / kg).The results showed that the salinity of the soil with anions and cations of nitrate, chlorine, potassium and sodium was significant at the level of 1%. However, there was no significant relationship between salinity of dust solution and bicarbonate, phosphorus and magnesium. The results showed that chlorine and sulfur elements were significantly enriched in dust compared to surface soils, and the southern study area with the highest concentration of chemical elements was found. Quartz, calcite, and albeit were the main minerals, and chlorite, elite, muscovite, and dolomite were identified as sub-minerals.

    Conclusion

    The results indicate that the chemical properties of dust have different time trends in the seasons. These changes can be attributed to changes in the probable origin of dust particles in different seasons and changes in the natural and human resources of dust production. High and positive correlation of chlorine ions, nitrate, and potassium and sodium ions with salinity in dust can be a reason for the origin of dust particles from soils of saline areas. Mineralogy of dust samples showed that the dust of the region contains minerals such as quartz, silica, calcite, albite, sodium feldspar, chlorite, dolomite, illite and calcium carbonate, some of which are similar. Clay mineralogy is topsoil in the study area. Minor changes in major and minor minerals in dust samples indicate the same and similar origin of dust production in the study area.

    Keywords: Chemical Properties, atmospheric dust, enrichment ratio, particle size.Yazd city
  • Mehry Akbary, Vahideh Sayad * Pages 37-74

    Climate change refers to changes in the direction of the mean of climatic parameters over a long period of time. Changes in the limit values and averages of climatic parameters are important consequences of climate change. This is scientifically different from climate fluctuations. Climate fluctuations are periodic and the deviations of the climatic parameters indicate the average and can occur in different time periods, but climate change is a general and widespread fluctuation in the climate of a region; currently, global warming is seen as part of climate change. Attention to climate change in recent years has become increasingly important due to the economic, social, and financial consequences of weather events. According to the Intergovernmental Panel on Climate Change, human intervention in global climate change is undeniable, although some researchers still believe that some climate change is unknown and that the mere human impact of climate change should not be confirmed. But the challenge of climate change in recent decades is very different from climate change in recent decades, one is that human intervention in nature has increased and the other is the rapid pace of climate change that has made it difficult to adapt.Given that none of the research on climate change has comprehensively addressed this issue in Iran, it was necessary to conduct a comprehensive study of the available resources, including the effect of climate change on hazards, hydrology, agriculture, urban and so on. Its effect is on the social and economic consequences that have taken place in Iran so far.This study was conducted using the library method and searching in authoritative scientific and research sources in relation to research on climate change in Iran and no data has been processed in it, so that the temporal and spatial changes of climate change over several The year has been studied and analyzed in Iran. It has also divided it into sub-sectors of agricultural climate, hydrology, urban, social and economic climate, and hazards based on studies conducted in various fields of climate change. First, keywords such as climate change and global warming were searched in reputable scientific databases such as Google Scholar, Science Direct, Magiran, SID, and the University of Tehran Library. In the next step, resources were categorized into separate study sections and different definitions of climate change. A variety of methods used to study climate change and the area under study were discussed, and finally the various conclusions were summarized and analyzed.Today, the phenomenon of climate change has attracted the attention of all researchers. Iran, as a region in the dry desert belt, has been strongly affected by the effects of climate change and therefore many studies have been conducted in various fields of climate change in Iran. The sequence is divided.The rise in border incidents in recent years has become a major concern for climatologists in recent years. The first effect of climate change is on atmospheric elements, especially temperature and precipitation. Therefore, it is important to investigate the changes in these variables in order to moderate the damage or adapt to the phenomenon of climate change.The World Water Organization emphasizes the need to research water resources, upsetting the balance of the climate system caused by rising greenhouse gases, and emphasizes the importance of studying the impact of climate change on hydrological parameters such as evaporation and transpiration. The country seems essential.One of the most important issues in the agricultural sector in recent decades, which has limited the production of crops, is climate change. This phenomenon changes the water resources of each region over time. It is essential to know the temporal and spatial fluctuations of meteorological parameters (such as temperature, precipitation, relative humidity, etc.) and its effect on the agricultural sector to manage water and agricultural resources and adopt appropriate strategies.Urbanization and urban development, along with population growth and the development of industrial activities and the wasteful consumption of fossil fuels, have greatly increased air pollution, with short-term and long-term disease exacerbating some climate fluctuations and environmental impacts, including changing time periods. Suitable in terms of comfort climate.In recent decades, the process of industrialization has accelerated dramatically. Population growth and the growing need for food have made the development of industries and factories inevitable, and this has made the phenomenon of climate change from a luxury issue a very serious one, at the forefront of negotiations between the leaders of large and small countries Is located.According to research conducted in Iran since the beginning of the global warming phenomenon, in general, the temperature is increasing and rainfall is decreasing despite high time and space variability. The temporal and spatial intervals of climate patterns have changed or their occurrence has been more or less than average. But extreme phenomena, such as drought, are more affected by climate change than others. This has weakened the Siberian low-pressure low and intensified the high-pressure side of the tropics. Although some studies have shown that rainfall increases in some areas, rising temperatures will increase evaporation and transpiration, and we will continue to face shortages of water resources in the future. As surface water levels drop and groundwater levels drop, dams will gradually lose their function, and the status of aquifers will shift from a critical state to a supercritical state, followed by the number and severity of events. Floods and droughts will increase. Increased evapotranspiration has increased the water needs of agricultural products. Although the length of the growing season has increased and the time of cultivation has changed, the effects of global warming and global warming have reduced crop yields. It has become a product, and food security, human health, and macroeconomics have been severely affected by water scarcity. In cities, too, climate change has increased air pollution, created a thermal island, and ultimately wiped out climate comfort. Climate change has also led to security and political disputes, mostly over water disputes. Regardless of the effects of climate on various projects, designers and experts are less successful in planning. A direct way to slow down global warming and climate change is to significantly reduce the use of fossil fuels and try to adapt to the effects of climate change, including increasing the intensity and frequency of droughts. Also, having knowledge and information plays an important role in the occurrence of protective and preventive behaviors against climate change. Finally, the results of evaluating climate change adaptation strategies based on social, economic and environmental indicators of water security show that in order to reduce system vulnerability in the coming period, while increasing economic water productivity in agriculture by increasing irrigation efficiency, agricultural activity will be reduced and compensated. Increase economic and social damage, service and industry activity.

    Keywords: Climate change, hazards, hydrology, agriculture, urban
  • Azar Zarrin *, Abbasali Dadashi-Roudbari Pages 75-90
    Introduction

    Climate change is one of the major threats of the 21st century. One of the major data sources for studying climate change is the general circulation model (GCM), which is widely used to assess and project past and future climate change and to manage regional risk hazards. GCMs can make significant assessments of temperature and precipitation. The application of individual models has high uncertainty. Therefore, in this study, applying an ensemble approach has been considered to project future temperature changes in Iran. The purpose of this study is to create a multi-model ensemble (MME) with bias-corrected CMIP6 models to project the temperature of Iran and the warm spell duration index (WSDI) in the near future (2021-2040).

    Materials and methods

    To evaluate the CMIP6 models in simulating the average annual temperature for the period of 1995 to 2014 (these 20 years were considered as the historical period), we used 120 synoptic stations in Iran. In this study, five CMIP6 models (GFDL-ESM4, MPI-ESM1-2-HR, IPSL-CM6A-LR, MRI-ESM2-0, UKESM1-0-LL) with a horizontal resolution of 0.5 degrees were used. Using intermediate (SSP3-7.0) and worst-case (SSP5-8.5) scenarios, annual temperature and heat stress were projected under climate change conditions for the near future (2040-2021).In this study, normalized root mean square error (NRMSE) and mean bias error (MBE) were used to validate the performance of the models. To correct the bias of CMIP6 models, Delta change Factor (DCF) method with 120 synoptic station was used. Then, independence weighted mean (IWM), were used to ensemble five models.In this study, in addition to temperature anomalies, warm spell duration index (WSDI) was also projected by 2040. The warm spell duration index is the number of days per year with at least 6 consecutive days when TX > TX90th, where TX is the daily maximum temperature and TX90th is the calendar day 90th percentile.

    Results and discussion

    Based on the Direct Model Output (DMO) in the climates of Sea of Oman and Caspian Sea coasts, all five CMIP6 models underestimated the average annual temperature (Chabahar and Rasht stations). However, CMIP6 models in other climates of Iran overestimated the average annual temperature. The mean bias of 1.00, 0.962, 0.983, 1.001, 0.936 degrees Celsius is compute for GFDL-ESM4, IPSL-CM6A-LR, MPI-ESM1-2-HR, MRI-ESM2-0 and UKESM1-0-LL, respectively. Therefore, UKESM1-0-LL and IPSL-CM6A-LR models are efficient models among the studied models for estimating Iran temperature, respectively. The temperature bias values fluctuate from -2.27 to 2.70 degrees Celsius in Iran. The average annual temperature based on MME-CMIP6 output fluctuates between 6.27 and 27.7 degrees Celsius. The coasts of the Persian Gulf and the Sea of Oman showed the maximum temperature and the northwestern regions of Iran showed the minimum temperature. The warm spell duration index varies between 3.48 to 12.5 days during the historical period. The temperature projected for both SSP3-7.0 and SSP5-8.5 scenarios show a further increase in the interior, northwest, north, and northeast of Iran. The average annual anomaly in Iran is estimated to be 1.13 and 1.26 degrees Celsius, based on SSP3-7.0 and SSP5-8.5 scenarios, respectively for the near future during the years 2021-2040.According to the SSP3-7.0 scenario, the minimum temperature anomaly of the country is 0.765 and the maximum is 1.227 degrees Celsius. Also, for the SSP5-8.5 scenario, temperature anomalies for minimum and maximum annual temperature are estimated to be 0.785 and 1.380 degrees Celsius, respectively. Projecting the time-series changes of the temperature in eight representative stations of Iran under the scenarios of SSP3-7.0 and SSP5-8.5 showed that the amount of warm spell duration varies in different regions of Iran. The anomaly of the warm spell duration index (WSDI) in Iran according to the SSP3-7.0 scenario will increase by at least 13.1 and at most 58.6 days. Also, the results related to the worst-case scenario (SSP5-8.5) have shown a minimum increase of 17.4 days and a maximum of 74.5 days in Iran.

    Conclusion

    Evaluation of direct output of five models from the series of Coupled Model Intercomparison project (GFDL-ESM4, MPI-ESM1-2-HR, IPSL-CM6A-LR, MRI-ESM2-0, UKESM1-0-LL) In the historical period (1995-2014) showed that although some models performed better in some climate regions of the country, the use of the direct output of individual models will increase the uncertainty in the results. For this purpose, using the independent weighted average (IWM) method, the output of the models was improved. The evaluation of the output of the ensemble model emphasizes this result.In general, the results of model validation showed that the output of CMIP6 models has higher performance for arid and semi-arid regions of Iran, whether before or after bias-correction. However, using either individual or bias-corrected and ensemble models in very humid climates (The northern parts of Iran) should be used with more caution because even with the correction of bias and doing ensemble, the positive bias is more than 2 degrees Celsius for the mentioned areas.The projection by using MME-CMIP6 show the annual temperature increase in near future (2021-2040). The average annual temperature anomaly will increase by 1.13 and 1.26 degrees Celsius, under the scenarios of SSP3-7.0 and SSP5-8.5 respectively, during the near future (2021-2040). The results indicate the very important role of unevenness in the heterogeneous distribution of temperature in increasing the average annual temperature of the country in the next two decades. The minimum temperature anomaly is projected in the southeast of Iran and the maximum in the northwestern and central regions.Projecting the warm spell duration index (WSDI) indicates an increasing anomaly of that in the country. The main hotspot of WSDI is on the southern coast of Iran, especially in the Persian Gulf area, which according to the results of the worst-case scenario will increase by 74.5 days by 2040. Analysis of changes in the average annual temperature of MME-CMIP6 shows that Iran will warm up more rapidly in the near future (2021-2040) than in the historical period (1995-2014). More warming, especially in high and snowy areas, will affect natural ecosystems and limit future access to water resources. Most of the interior, east and south of Iran has arid and semi-arid climate and a sharp rise in temperature under the worst-case scenario (SSP5-8.5) leads to environmental degradation and intensification of drought on the one hand and increased desertification on the other.

    Keywords: Temperature projection, CMIP6 Models, Ensemble model, WSDI index, Iran
  • Hossein Asakereh *, Sayed Abolfazl Masoodian, Fatemeh Tarkarani Pages 91-107

    A Discrimination of Roles of Internal and External Factors on the Decadal Variation of Annual Precipitation in Iran over Recent Four Decades (1975-2016)IntroductionAccording to Intergovernmental Panel on Climate Change (IPCC) the Earth's climate has been changed during recent century (IPCC, 2007). These changes may continues for the next century. The changes have happened in two ways, log- term change (trend) and variation (in form of Oscillations, phases, shifts, and persistence) (Asakereh,2017). Moreover, some of these changes are due to internal factors of a region, whilst some of them result from external culprits of a given region. The distinguish between these two groups of factors is an important scientific effort to understand the changes mechanisms governing them. The emerge of climate changes and climate variation can be traced by investigation of some sensitive climate elements. One of those chaotic elements is precipitation which experiences changes in different tempo-spatial scales (Goudi, 1994). Most of these changes, specially the trends, are studied in global (Todorov, 1985; Vining and Griffiths, 1985; Diaz et al. 1989) and national (Askari and Rahimzadeh, 2003; Asakereh,2004; Zahedi et al., 2007; Katiraie , 2007; Mohamadi, 2012; Ekhtesasi et al. 2015; Nazeri Tahrudi, 2016) scals. In the climatology literature (Singh et al. 1995; Ghayur and Masoodian, 1996; Glazirin, 1997; Mojarrad and Moradifar, 2003; Asakereh, 2004; Raziei and Azizi, 2009; Asakereh and Seifipour, 2013) spatial changes of precipitation was attributed to spatial coordination (longitude and latitude) and topographic features (elevation, slope magnitude and aspect). The temporal changes in precipitation in association with these topo-spatial factors has not been considered in details and in proper ways in climate researches. In current study we put the spotlight on the decadal variation in relation with the topo-spatial features as a representative of climate change and as a vital context of research. Accordingly, a regression model is adopted so as quantify the effects of topo - spatial factors effecting variability of precipitation over recent four decades.Materials and methodsIn order to achieve the aim of current study, two dataset were adopted; a national precipitation dataset, Esfezari, and Digital Elevation Model (DEM):The third version of Esfezari dataset is result from Kriging interpolation of daily record of 2188 synoptic, climatologic, and rain gauge stations for 46 years (1970-2016) with 10 km resolution. The 16801 daily maps with 167×205 pixels were created accordingly. Consequently, the dataset include dimensions of 167×205×16801. The DEM data with 10 meters spatial resolution was adopted from The U.S. Geological Survey which was provided by "Astet" satellite images. This dataset was applied to extract the topographic features (elevation, slope and its aspect) for Iran. To start with, the annual precipitation for the entire under investigation period (1970-2016) was analyzed according to abovementioned data. In the second place, the topo-spatial distribution of precipitation for four decades ended up to 2007-2016 was compared in an analyzing effort by using linear and non-linear correlation. In this stage, according to Law of Parsimony, it is revealed that linear correlation illustrate the relation between precipitation and topo - spatial factors in proper way. Moreover, A multivariate linear regression fitted on the five topo-spatial elements for every under study decade so as to detect precipitation accordingly. The regression model can be expressed as follow: where refers to annual precipitation in th pixel which is detected by the topo - spatial factors and considered the internal- cause precipitation. and are latitude and longitude, respectively. In the above regression model, , and are elevation, slop, and aspect of slop, respectively. Consequently, the external - cause precipitation is the model residual. Finally, the descriptive characteristics of precipitation maps of internal-cause and external - cause were analyzed. Results and discussionGeneral Features of Iran PrecipitationThe general feature of precipitation over Iran shows a decreasing trends from west to east and from north to south. The coast of Caspian Sea and the summits of Zagros Mountain chain receive the highest values of precipitation. The spatial average of annual precipitation is about 250.5 mm. The strongest relationship between precipitation and topo-spatial factors is related to longitude in negative way. This feature is reflected in eastward decreasing of precipitation. The determine coefficients for latitude and elevation are 13% and 4.5%, respectively.The variation of effects of internal and external factors In spite of the stability of the determine coefficients of all regression models for all decades, some of topo - spatial factors have noticeable variation. This feature refers to the fact that increasing in the effect of one factor may decrease the effect of other one(s). The models, however, illustrate a stable feature for precipitation over all four under study area during four decades. Consequently, the external factors are the main culprits in decadal changes of annual precipitation. Our finding showed that in the first decade the ratio of factors was 52.38% which increased gradually to 54.08% , 58.44%, and 59.72% among of four under the rest decades (Table 1). This refer to the fact that the changes in variation of precipitation is in association of global changes.Table 1: The areas under the effects of variation due to internal and external factors (%)Priod The percent of the country due to ---effects internal externalFirst decade 47.62 52.38Second decade 45.92 54.08Third decade 41.56 58.44Forth decade 40.28 59.72Entire period 44.38 55.62ConclusionThe climate and precipitation climatology of Iran is effected by internal and external factors, due to geographic features of the country. The internal factors include spatial (latitude and longitude), and topographic (elevation, slop and its aspect) features. In current study, in order to discriminate internal and external characteristics which effects precipitation variation we fitted a multivariate linear regression on internal factors to separate them out and distinct external factors. Accordingly, our finding revealed that the ratio of external factors in variability of precipitation increased from the first decade (52.38%) to the last decade (59.72%). This result is in line with previous studies (Khodadi et al. 2013; Farajzadeh and Ahmadian, 2014; Darand, 2015; Karimi et al., 2018). The most influenced area from the variations of external factors are internal parts rather than marginal parts of the country. 

    Keywords: Iran, Precipitation, climate change, Decadal Variation, Precipitation Variability
  • Mohammadsadegh Keikhosravi Kiany *, Seyed Abolfazl Masoodian Pages 109-121
    Introduction

    Snow cover plays an important role in the water and energy cycle of the world due to its high albedo and thermal properties and it can also reflect global climate change (Dozier et al., 2008; Shi, 2012). Precise monitoring of the extent of snow cover is an issue that has received much attention (Lampkin and Yool, 2004). Monitoring snow parameters, such as the extent of snow cover and snow equivalent water, are a challenging topic for meteorologists and climatologist. Snow cover plays an important role in balancing the earth's energy due to its high albedo and affects the climate (Akyurek et al., 2010). Many studies have been conducted to investigate snow cover and its changes. for example, Khadka et al. (2014), used the MODIS data for the period 2000–2009 to analyze snow trends in the Tamakoshi Basin of the Himalayan Mountains, The findings of the researchers showed that during the ten years of the study, there was a decreasing trend in the area of snow zones during spring and winter, while the area of snow zones had an increasing trend in the autumn season (Khadka et al. 2014). Sharma et al. (2012) applied MODIS data for the years 2000–2011 to analyze the snow trends in the Jalom River Basin and its sub-basin located in the northwest of the Himalayas. The results showed decreasing trend in all sub-basins with the highest negative rate for Banihal sub-basin (Sharma et al. 2012). Maskey et al. (2011) studied the trend of snow cover in and around Nepal for the years 2000–2008. For this purpose, they applied MODIS data. The findings show that in January for three elevation zones below 6000 m and in March for two elevation zones above 5000 m snow cover trend are seen. In the fall, snow cover showed increasing trend for four altitudes above 4000 m (Maskey et al).

    Materials and methods

    In this study, the daily data of MODIS Terra (MOD10A1) and MODIS Aqua (MYD10A1) version 6 were applied for the period from 1380/7/1 to 1397/6/31. One of the problems that is always a big obstacle to monitoring snow cover is the cloud issue. Clouds cause the underlying snow cover to be hidden from the satellite view. To reduce cloudiness and better observation of snow cover, various methods and strategies have been suggested by various researchers to minimize cloud cover effects. The applied filtering methods included combination of MODIS Terra and MODIS Aqua, spatial combination with four pixel neighbor and 1 to 5-day temporal windows. All calculations were performed using programming operations in MATLAB software and at the climatological laboratory of the University of Isfahan.

    Results and discussion

    In order to better present the research findings and to classify them, calculations related to the accumulation and melting timing of snow cover in Iran have been provided spatially and temporally for each of the accumulation and melting parameters. Climatological survey of snow cover accumulation in Iran shows among the first days that the earth is covered with snow and the elevation there exist a strong relation, in other words, the first days of snow cover occur at the highest altitudes and slowly move to the lower elevations as we move toward autumn. Analyses shows the first days of snow cover in the first decade of Mehr are seen on the Alborz Heights and the Sabalan Heights in the northwest. Snowfall days in other northwest elevations begin around the second half of late Mehr. The onset of the snow cover season on the central Zagros highs begins around the first decade of Aban and covers many of the lower elevations until late Azar. It seems that the delay of the onset of the snow cover season on the Zagros Mountains compared to the northern and northwestern highlands of the country is due to the delay in autumn rainfall rather than the necessarily warmer temperature.A long-term study of the average snow cover melting in Iran shows that there is a very strong relationship between altitude and the last day when the ground is covered with snow. The analyses show that, on average, the last day when the ground is covered with snow starts from lower altitudes and slowly migrates to higher altitudes. For example, in the lower elevations of the Zagros Mountains the snow cover on the ground is melted in the middle of February, in the higher elevation areas due to the colder weather the last day when the ground is covered in snow are seen in the late of winter. However, there is snow cover in the Zardkouh highlands until the end of June and even early July, and afterwards, these areas lose their snow cover. On the Alborz Mountains due to their higher altitude and higher latitude, snow cover will persist even in some areas until late Amordad and early Sharivar. During the months of snow accumulation in Iran, which covers the months of Mehr to Azar, snowline moves downwards at an average rate of 54 m / day, while during the months of snow melting (Dey to Shahrivar) snowline migrate to higher altitudes at the rate of 15 meters per day.

    Conclusion

    The purpose of the present study is to study the climatological accumulation and melting of snow-covered days in Iran. In this regard, the sixth version of the MODIS Terra and MODIS Aqua daily data at the spatial resolution of 500 × 500 m for the period from 1380/7/1 to 1397/6/31 were downloaded from the NASA Web site. In order to reduce the cloud effect on the data, three data refinement techniques were applied on the raw data including combination of MODIS Terra and MODIS Aqua, spatial combination with four pixel neighbor and 1 to 5-day temporal windows were applied to the raw data. The findings of this study show that the first snow-covered days are seen in the first decade of Mehr over the Alborz and Sabalan highlands and gradually snowline stretches to lower altitudes at 54 m / day. But during the melting months of snow cover, which includes Dey to Sharivar, snowline migrates to higher altitudes at a rate of 15 m / day. The reason for the slower rate of snowmelt migration to higher altitudes in the melting season can be attributed to the highly effective role of temperature in the melting season, but in the snow cover accumulation season, the role of temperature and precipitation mechanisms lead to the snow cover moving to lower altitudes.

    Keywords: Iran, Snow accumulation, snow melting, snowline, MODIS
  • Mohammad Mehdi Hoseinzadeh *, Nilofar Barkhordari Pages 123-140
    Introduction

    Bank erosion is a severe problem to any fluvial system as it can generate up to 90% of the total sediment yield from a catchment It is also considered a hazard because it causes loss of lives and properties. The bank erosion and displacement of river planform change, each year, large areas of agricultural land and residential areas and coastal installation are exposed to destruction. The Haft Cheshmeh river located in the village of Razjard in Rudbar Alamut region ( Moaalem kelaye), northeast of Qazvin province‚ with longitude 50˚10ˈ14 and latitude 36˚ 20ˈ27, experiences severe bank erosion in several parts of its course.. This area located on the southern hillside of Alborz and south of Alamut in the mountainous area. The study area is on the southern hillside of Alborz in the Alamot section. The length of the studied route of the river is approximately 11 km and it flows near the villages of Razjerd‚ Rashteghon‚ Mianber and Shengher.

    materials and methods

    In this research were used from the topographic map (1:25000) of National Cartographic Center of IRAN (NCC) and Google images for the demarcation of the Haft Cheshmeh basin boundary and flow path of the river. Meander curve, vegetation cover, and other parameters of the bank have been measured from from Google images and field observations. In this study, the method Bank Erosion Vulnerability Zonation (BEVZ) has been used for investigate the factors affecting (rainfall erosivity, lithological factor, bank slope, meander index, river gradient, soil erosivity, vegetation cover, and anthropogenic impact ) the instability and bank erosion of Haft Cheshmeh river. After collecting data and using from available parameters, the reaches and cross sections are selected. The base on six parameters data, general weightage values have been assigned to each of them.. this model Interprets data by weighting variables and It is actually a proposed model based on GIS. Finally, it prepares a map of the river zoning according to the parameters mentioned. Based on this zoning, the severity of the vulnerability is divided into 5 categories: very high, high, medium, low and very low. At the end when all cross sections are scored‚ map of cross sections is prepared and zoned based on weights assigned to areas susceptible to instability and bank vulnerability.

    results and discussion

    The bank slope map of the study area indicates that the most of the river banks of the Haft Cheshmeh river belongs to the moderate to gentle category of slope. The right side of reach 10 is in Very steep category in terms of side slope. According to the results, In the case of the meander index, the first reach is in the meander class and the rest of the reaches have straight pattern. In the soil erodibility factor, most bank river were in the class very gentle to gentle. Also in the left bank of reach 1, the right and left bank of reach 8 are in very high class. In the lithology factor, all reaches belong to the moderate category and only The lower part of the side of the reach 8 belongs to the very high category. There are also bed samples of all reaches of river in the low category.The river gradient is considered as the triggering factor of river velocity that controls river erosion. Longitudinal slope at all reaches in Haft Cheshmeh river ranges from gentle to moderate category. Although in the height of 1710-1720 and 1700-1690 are in high category. In the vegetation parameter, most reaches are in scattered class and also reaches 4, 5 and 9 have high vegetation. In the human activities parameter, reaches 1-5 and 8.9 are in the medium category due to agricultural and garden land use. In reaches 6 and 9, human activity is in high category. According to the results, all reaches except reaches of 5 and 9 have received average score. All of these reaches had moderate erosion vulnerability. According to the scores obtained and field observations, reaches 1 to 4 had a lot of vegetation. Also the soil erosion parameter in these reaches is in the gentle category and the meander index has the lowest score. The right bank of reach 5 has a slow erosion rate‚ but the left bank of this reach is high erosion. Because there is an bend at reach 5 that causes the left bank slope to increase and despite much vegetation, erosion has increased and the roots of the trees on this bank also show a lot of protrusions. But on the right bank, the gravely point bar has caused the wall slope to decrease and the amount of shear stress applied to it is low. As a result, it is less vulnerable to erosion. The right and left bank of reach 9 are very vulnerable, because in field observations, was observed in upstream of this reach a sedimentary barrier that caused the flow path to change and Channel walls on both sides become steep. At this reach, shear stress is high and also human activities have the most score.

    Conclusion

    The results showed that most of reaches in Haft Cheshmeh river are in moderate condition in terms of susceptibility to erosion. But in 8 and 9 reaches, due to high human activity in the river, they were in the middle to high class in terms of risk. Also, in all reachs except reach 10, are in the middle to high class due to the sensitivity of the side materials to erosion. A study of erosion sensitivity at different reach of Haft Cheshmeh river showed that more erosion occurs in areas where there is no vegetation or vegetation is scattered‚ also it is more susceptible to erosion. This study showed that vegetation and bank protection plays a key role in riverbank sustainability in this region . Evaluation of erosion using Bank Erosion Vulnerability Zonation method showed that vegetation is a protective factor along the river and human activities and meander index are two driving factors in the development of vulnerability and erosion.

    Keywords: Bank erosion, BEVZ, Channel vulnerability Haft Cheshmeh, qazvin
  • Ali Reza Karbalaee Doree *, Zahra Hedjazizadeh, Seyed Abolfazl Masoodian Pages 141-155
    Introduction

    The main sources of albedo change are variations in snow cover, variations in soil moisture, droughts, and variations in vegetation phenology, forest fires, and land use/ cover changes directly related to human activities, such as deforestation, irrigation, and urbanization. Forests obtain lower albedo values than shrubs, dry crops, grasslands, and bare soils. As a result, the conversion of forests to these land cover types leads to increases in surface albedo. This potentially has local and regional feedback, since an increase in surface albedo leads to a reduction in net radiation, turbulent heat fluxes, convective clouds, and precipitation, leading to a drier atmosphere Furthermore, black carbon decreases the surface albedo when deposited on snow and glaciers because it is incorporated in snowflakes, darkening snow and ice surfaces and increasing surface melt. Aerosols like dust transferred into the atmosphere and transported by the wind into the mountains where it settles on snow and glaciers, reducing albedo and leading to enhanced warming at higher elevations. It is noted that even though precipitation is the main driver of variations in soil moisture, its impact on albedo is controlled by evaporation, soil type, irradiation, vegetation, and topography. The present paper aims to evaluate the spatiotemporal variations of white sky albedo in Iran. For this, daily Albedo datasets from Moderate Resolution Imaging Spectroradiometer (MODIS) from onboard Aqua and Terra (MCD43A3v006) were applied from 2000 to 2019 with a spatial resolution of 500 × 500 m. MODIS provides black-sky albedo for direct and white-sky albedo for isotropic diffuse radiation at local solar noontime. For this, daily white sky albedo datasets from Moderate Resolution Imaging Spectroradiometer (MODIS) from onboard Aqua and Terra (MCD43A3v006) were applied. One of the main applications of the principal component analysis (PCA) is climatic zoning which is a method of determining environmental changes in temporal dimensions. A plethora of studies have been conducted using principal component analysis in the field of climatology but little has been done in relation to the albedo variation. To the best of the authors’ knowledge, this study uses a technique that has not been applied in scientific texts related to Modis albedo data. The questions that we will address in this study include: what is the temporal-spatial behavior of white sky albedo in Iran? How many components explain the variation of white Sky Albedo? What factors will distinguish white sky albedo in Iran?

    Materials and methods

    In this investigation, daily white sky albedo datasets from Moderate Resolution Imaging Spectroradiometer (MODIS) from onboard Aqua and Terra (MCD43A3v006) were applied for the period of 2000-02-24 to 2019-06-03 (7040 days) with a spatial resolution of 500 × 500 m. Among the various MODIS datasets, white sky albedo datasets were extracted. The daily white sky albedo was averaged over the 19-year period for each pixel inside the border of Iran. The size of this array was 7541502 pixel *12month. Long-term monthly and seasonal means were also calculated by the available time series data. In the next step, the PCA method was applied to analyze the spatio-temporal variations of albedo in Iran. PCA is a method to reduce the number of the data and convert them into several finite components so that these few components explain the largest amount of the variance. This procedure is searching for the variable with the largest amount of the variance in space (PCA was invented in 1901 by Karl Pearson , and it was later developed by Harold Hotelling in the 1930s. In this method, initial variables are converted into n principal components each being a linear combination of the variables. In this way, the first principal component has the largest possible variance, and the components afterward explain a smaller percentage of the variance. Principal component analysis leads to the analysis of space-time array into two time-array and space-array. In this case, it is possible to identify what important spatial patterns the primary data have and at what time periods each of these patterns has been active or inactive. Because the principal components are finite, the temporal and spatial patterns introduced by the first component are more important than the temporal and spatial patterns of subsequent components.

    Results and discussion

    The long-term average of Iran's white sky albedo was calculated; The results showed that the average albedo of spring, summer, autumn and winter in Iran 14.99%, 16.06% , 15.53%, and 19.58%, respectively. The evaluated long-term mean white sky albedo for each season showed that the highest value had occurred in winter. The dramatic increase in this value was placed along the Zagros, Alborz, Sahand, and Sabalan Mountains which exceeds 90 to 100 percent in some places. In the next step, the temporal-spatial variations of white sky albedo values in Iran were analyzed using principal component analysis, and the results showed that the three main components are able to explain 97.7% of the data variation. The first component explains more than 73%, of the total changes, the second component more than 20.8% and finally the third component explains more than 3.9% of the changes.

    Conclusion

    Spatial analysis revealed that the values which are higher than the mean are places in highlands and mountainous regions of Iran, such as the Zagros and Alborz Mountains, Sabalan, Sahand mountains and Zard Kuh-e Bakhtiari, which are associated with snow cover Therefore, the first component was named as snow cover as the maximum variance of albedo was explained by snow cover. The spatial analysis of the second component revealed that higher values were placed in small areas across Iran including, Hajaligholi desert Gavkhuni wetland, Qom salt lake, Sirjan salt lake parts of Loot desert. In the second component, most of the cell's scores upper of average in Iran corresponded to areas covered with salt. As the maximum variance is explained with salt cover, therefore, it can be named as the salt land. Spatial analysis indicated that in very limited parts of Alborz, Zagros, Alam-Kuh Mountain , Sahand, and Sabalan mountains Kino Mountain values are mostly positive which is related to the glaciers (regions with appropriate conditions to keep the snow cover in most of the year) and is the origin of the seasonal or permanent rivers Therefore, according to the cell scores (upper of average in Iran) in the third component, it was found that these cells corresponded to the , so it was named as the glacier component.

    Keywords: MODIS, White Sky Albedo, Principal component analysis, Snow Cover