دانشگاه محقق اردبیلی مدل سازی و مدیریت آب و خاک 2783-2546 6 1 2026 03 21 Analysis of changes in maximum snow cover duration in Northwest Iran تحلیل تغییرات بیشینه ماندگاری متوالی برف‌پوش در شمال غرب ایران 208 225 4111 10.22098/mmws.2025.18162.1651 FA برومند صلاحی استاد، گروه جغرافیای طبیعی، دانشکده علوم اجتماعی، دانشگاه محقق اردبیلی، اردبیل، ایران. امیرحسین حلبیان دانشیار، گروه جغرافیا، دانشگاه پیام نور، تهران، ایران عباس کاشانی دانشجوی دکتری آب و هواشناسی، گروه جغرافیای طبیعی، دانشکده علوم اجتماعی، دانشگاه محقق اردبیلی، اردبیل، ایران Journal Article 2025 08 22 Extended Abstract Introduction Variations in snow cover, along with its phenological aspects such as the duration, onset, and cessation of snowfall, are critical to understanding mountainous ecosystems. These changes heavily influence water resource accessibility in nearby regions. Snow cover serves as a vital component in energy and temperature regulation and is intricately connected to hydrological, biological, chemical, and geological processes. Furthermore, it plays a significant role in both the hydrological cycle and the overall energy balance of the environment. Recent research indicates that mountain regions are undergoing temperature increases at twice the global average rate, with this trend intensifying at higher altitudes. As a result, mountains have come to be regarded as critical indicators for monitoring climate change over the past few decades. This study focused on examining variations in the maximum snow cover persistence in the northwest of Iran, analyzed across monthly, seasonal, and annual time scales. Materials and Methods This study utilized MOD10A1 and MOD10A1 version 6 products from the Terra and Aqua satellites to conduct a daily analysis of snow phenology spanning the years 2003 to 2020. These datasets, accessible as digital network data derived from the NDSI index, were retrieved through Earthdata's online portal at earthdata.nasa.gov. A threshold value of 0.1 or higher was applied for snow cover estimation to facilitate the conversion of snow cover data into binary format. All adjustments, data processing, and analytical procedures were carried out using Python. Cloudiness reduction was accomplished using data fusion algorithms, spatial neighborhood filtering, and temporal filtering techniques. By combining the Terra and Aqua databases and applying spatio-temporal filtering with a threshold range of 0.1 to 1, a binary database of daily snow cover was generated. This database served as the basis for evaluating snow cover persistence and maximum snow cover persistence parameters, which were analyzed across monthly, seasonal, and annual intervals. Results and Discussion During January, the maximum consecutive snow cover pattern is marked by two prominent peaks in the Sahand and Sabalan Mountains, specifically around Ghoch-Goli Daghi and Sultan-Sabalan, with intervals spanning 20 to 30 days. In February, the MaxSCDur indicates a noticeable rise in snow cover duration, influenced by various surface roughness features and an expansion of areas showing high persistence. By March, this pattern shifts as regions of high persistence shrink and areas with low persistence expand. As the cold season concludes, the snow cover significantly decreases. The spatial pattern observed in April reveals a notable reduction in snow cover, with snow retreating from mid- and low-altitude areas while remaining concentrated on high peaks. This pattern underscores the crucial influence of altitude on the persistence of snow cover during the melting season. Between May and September, spatial patterns for MaxSCDur exhibit a gradual decline in duration, decreasing from 20.87 to 24.24 days in May to just 5.91 to 7.5 days by September. During August and September, the maximum consecutive snow cover is confined exclusively to the summit of the Sabalan Glacier. From October to December, MaxSCDur spatial patterns display an upward trend in frequency, with durations increasing from 20.84 to 23.24 days in October to approximately 30 to 31.25 days by December. The MaxSCDur pattern for October highlights a notable increase in snow cover range and duration as autumn sets in, marked by declining temperatures, especially at higher altitudes. Analysis of the spatial distribution for winter’s MaxSCDur reveals the highest snow cover duration at the summits of Sabalan and Sahand, ranging between 25.6 and 29.25 days. The spring pattern shows a reduction in MaxSCDur, decreasing progressively from southern to northern parts of the studied area when compared to winter. During summer, the maximum consecutive snowfall period is limited to 0–2 days across most regions, except for notable peaks such as Sabalan (4–20 days), Sahand, Avarin, Barda-Rash, Kale-Shin, and Qandil (2–4 days). The autumn MaxSCDur pattern records durations of 4–20 days in Sabalan and its slopes, 4–8 days in the Sahand and Bazgush mountains, and 4–6 days in Qara-Dagh, Barda-Rash, Dalampar, and Kale-Shin. On an annual scale, areas with extended MaxSCDur have shown strong regression towards central and high troughs during 2010 and 2018. Conversely, years such as 2008, 2012, and 2017 exhibit visible rock formations predominantly at higher altitudes, encompassing foothills and slopes within these geomorphologic units. Conclusion The MaxSCDur map for February reveals that areas with high snow cover persistence have expanded and intensified when compared to January. An evaluation of the MaxSCD models for November and December indicates a marked increase in both the thickness and duration of snow cover across all snow types as the cold season advanced. December serves as the turning point when full winter conditions are established in the study area. In a seasonal context, winter is characterized by peak precipitation levels and prolonged snow cover, especially across rugged terrains throughout the region analyzed. As spring arrives, rising temperatures lead to the gradual retreat and melting of snow cover. By summer, most regions are entirely devoid of snow, with only fleeting patches visible on the highest summits. Autumn brings a shift as falling temperatures initiate the gradual accumulation of snow at elevated altitudes, resulting in a higher maximum snowfall compared to summer. These patterns reflect a transition from warmer to colder conditions and signal the region's preparation for increased winter precipitation. Historical observations show that minimum MaxSCD values occurred in 2010 and 2018, while peak values were recorded in 2008, 2012, and 2017 within the study area. در این پژوهش با هدف شناسایی و واکاوی تغییرات فضایی- زمانی بیشینة ماندگاری متوالی برف‌پوش در شمال غربی ایران از فرآورده‌های روزانه برف مادیس (MOD10A1 و MYD10A1) در دورة 2020-2003 استفاده شد. ابتدا، داده‌ها بر اساس آستانة حداقل 1/0 باینری شد. در گام بعدی اثر ابرناکی با استفاده از ترکیب داده‌ها، فیلتر مکانی و زمانی کاهش داده شد. سپس، بیشینة ماندگاری برف‌پوش (MaxSCDur) در هر یاخته در شبکة رستری در بازظ ماهانه، فصلی و سالانه محاسبه و نقشه‌های پهنه‌ای ترسیم شد. نتایج نشان می‌دهد که پهنه‌های با ماندگاری بالا در فوریه نسبت به ژانویه گسترش و افزایش یافته است. در این ماه بیشینة میزان MaxSCDur با مقادیر 28-20 روز متعلق به قلل کوهستانی و کمینة آن با 3-0 روز مربوط به نواحی پست شمال شرقی کوه‌های طارم است. الگوی مارس کاهش گستره پهنه‌های با ماندگاری بالا و گسترش مناطق با ماندگاری کم را نشان می‌دهد. الگوی آوریل نشان از کاهش چشم‌گیر ماندگاری برف و تمرکز برف در قلل مرتفع دارد. الگوهای ماه‌های می تا سپتامبر کاهش مقادیر این نمایه را نشان می‌دهد. بر اساس الگوهای اکتبر تا دسامبر، بیشینه میزان MaxSCDur در قلل ارتفاعات از 23-84/20روز به 31-30 روز افزایش یافته است. کمینة میزان آن در این دورة مربوط به نواحی پست با 3-0 روز است. الگوی زمستانه، بیشینة میزان MaxSCDur را در قلل سبلان و سهند با مقادیر 6/29-25 روز و کمینة آن را در نواحی پست با مقادیر 20-0 روز نشان می‌دهد. الگوی بهاره نسبت به زمستانه نشان از افت MaxSCDur از جنوب به‌طرف شمال در پهنه مطالعاتی دارد. بر اساس الگوی تابستانه، MaxSCDur فقط در قله سبلان با 20-4 روز، در سهند و قلل ارتفاعات غربی منطقه با 24-2 روز نمودی آشکار دارد. بیشینة ماندگاری برف‌پوش پاییزه نسبت به الگوی تابستانه فقط در سرزمین‌های مرتفع کوهستانی افزایش نشان می‌دهد و همچنان خط‌الرأس سبلان با 20-4 روز از بیش‌ترین مقدار برخوردار است. بر اساس الگوهای سالانه MaxSCDur سال‌های 2010 و 2018 در فاز کمینه و سال‌های 2008، 2012 و 2017 در فاز بیشینه قرار داشته است. یافته‌های این پژوهش می‌تواند در مقولة منابع آبی، توان‌های اکولوژیکی و مدیریت نواحی کوهستانی مورد استفاده قرار گیرد.

https://mmws.uma.ac.ir/article_4111_60cbab9ffc3459f7853ba243ad33b00d.pdf