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شناسایی فصل بارش در ایران | ||
| فیزیک زمین و فضا | ||
| مقاله 11، دوره 52، شماره 1، خرداد 1405، صفحه 179-194 اصل مقاله (1.34 M) | ||
| نوع مقاله: مقاله پژوهشی | ||
| شناسه دیجیتال (DOI): 10.22059/jesphys.2026.408873.1007746 | ||
| نویسندگان | ||
| محدثه وزیری مهر1؛ حسین عساکره* 1؛ محسن حمیدیان پور2 | ||
| 1گروه جغرافیا، دانشکده علوم انسانی، دانشگاه زنجان، زنجان، ایران. | ||
| 2گروه جغرافیا و برنامهریزی محیطی، دانشکده جغرافیا و برنامه ریزی محیطی، دانشگاه سیستان و بلوچستان، سیستان و بلوچستان، ایران. | ||
| چکیده | ||
| شناسایی ویژگیهای زمانی و مکانی فصل بارندگی در ایران، از اهمیت بالایی در مطالعات اقلیمشناسی، مدیریت منابع آب و برنامهریزی کشاورزی برخوردار است. در این پژوهش، با استفاده از روش میانگین متحرک ۳۰ روزه بر دادههای بارش روزانه و آستانه بلندمدت ۳۶۶ روزه، شاخصهای آغاز، پایان، طول فصل بارندگی و نسبت بارش فصل بارندگی به بارش سالانه برای کشور ایران استخراج و تحلیل شدند. نتایج حاصل از نقشههای فضایی نشان داد که ایران طی دوره آماری ۱۹۶۰ تا ۲۰۲۳ دو الگوی بارشی متمایز را تجربه کرده است: در دوره اول، فصل بارندگی بهصورت گسترده و پیوسته سراسر کشور را در برگرفته و تمرکز بارش در فصل سرد سال، از نواحی غربی به نواحی شرقی منتقل شده است؛ در حالیکه در دوره دوم، فصل بارندگی بهصورت منطقهای و پراکنده ظاهر شده و نواحی مرکزی کشور از الگوی بارشی منظم خارج شدهاند. تأخیر در آغاز فصل بارندگی و پیشافتادن پایان آن در بسیاری از مناطق، بهویژه در جنوبشرق کشور، منجر به کاهش طول فصل بارندگی و افت محسوس شاخص بارش شده است. این تغییرات با جابهجایی مسیر چرخندهای مدیترانهای، کاهش همگرایی شار رطوبتی، تضعیف جریان رودباد و افزایش دمای سطح دریاهای اطراف ایران همراستا بودهاند. یافتهها بیانگر آن است که فصل بارش در ایران از نظر زمان آغاز، پایان و طول، تنوع مکانی قابلتوجهی دارد. آغاز بارشهای فراگیر عمدتاً از سواحل خزر شروع شده و بهتدریج به سایر مناطق گسترش مییابد و طول فصل بارش بین حدود ۴ تا ۸ ماه متغیر است. نتایج تحلیلهای آماری بیانگر نقش معنادار ارتفاع و عرض جغرافیایی در تغییرات مکانی بارش، بهویژه در شمال، جنوب و شرق کشور است. در مجموع، توپوگرافی و موقعیت جغرافیایی نقش تعیینکنندهای در الگوی زمانی و مکانی فصل بارش داشته است. | ||
| کلیدواژهها | ||
| ایران؛ بارش؛ فصل بارش؛ تحلیل فضایی؛ فصل بارش فراگیر | ||
| عنوان مقاله [English] | ||
| Identifying the Rainy Season in Iran | ||
| نویسندگان [English] | ||
| Mohadeseh Vaziri Mehr1؛ Hossein Asakereh1؛ Mohsen Hamidianpour2 | ||
| 1Department of Geography, Faculty of Human Sciences, University of Zanjan, Zanjan, Iran. | ||
| 2Department of Physical Geography, Faculty of Geography and Environmental Planning, University of Sistan and Baluchestan, Sistan and Baluchestan, Iran. | ||
| چکیده [English] | ||
| The rainy season represents a key manifestation of the climate system’s response to atmospheric general circulation, synoptic-scale interactions, and land–atmosphere thermodynamic conditions. The timing of the rainy season—its onset, cessation, and duration—reflects the trajectories of cyclones, the intensity and positioning of westerlies, and variations in moisture flux convergence. Iran, situated within the arid and semi-arid subtropical belt, exhibits high spatiotemporal variability in its rainy season due to its location at the intersection of Mediterranean, Sudanese, Caspian, and Monsoon influences. Consequently, identifying the rainy season using a physically based approach with daily precipitation data is essential for understanding the mechanisms governing regional precipitation. This study aims to extract and analyze the temporal and spatial characteristics of Iran’s rainy season and interpret them within the framework of the governing atmospheric processes. Daily precipitation data from 72 synoptic stations across Iran were analyzed for the period 1960–2023. Stations were selected to ensure appropriate spatial coverage, topographic diversity, and minimal data gaps. The rainy season was identified using a 30-day moving average applied to daily precipitation series, with the long-term mean over 366 days serving as the reference threshold. Any period of at least 30 consecutive days in which the moving average exceeded the threshold was classified as a rainy season. Transition points from dry to wet and vice versa defined the onset and cessation, respectively. Based on this method, indicators including the onset, cessation, duration of the rainy season, and the proportion of seasonal precipitation relative to annual totals, were extracted. To evaluate the influence of spatial factors on rainy season variability, multivariate regression and Pearson correlation analyses were conducted between geographical variables (latitude, longitude, and altitude) and rainy season characteristics. The analysis revealed that Iran exhibits both a general and a regional rainy season regime. The general rainy season extends across the country, whereas the regional rainy season occurs in the northwest, parts of the Caspian Sea coast, and the southeast of Iran. The general rainy season initiates in areas along the Caspian Sea coast and gradually extends westward, northwestward, eastward, and southeastward. This pattern aligns with the expansion of the Siberian high, weakening of the subtropical high-pressure system, and Mediterranean cyclone activity. Cessation occurs first along the Caspian Sea coast, followed by the central and southern regions. Maximum rainfall duration is observed in the northwest, while the central and southeastern regions experience the shortest durations. The length of the general rainy season ranges from approximately four to over seven months. The ratio of seasonal to annual precipitation indicates a high concentration of cold-season rainfall (>85%) along the southwest to eastern regions, consistent with large-scale cyclonic dominance. In contrast, the Caspian Sea coast and northwestern coastal areas exhibit greater temporal dispersion of precipitation due to the interaction of synoptic and convective systems. The regional rainy season is primarily influenced by mesoscale processes in the northwest and monsoon flows in the southeast. Its duration exceeds two months in the northwest but is less than one month in the southeast. Statistical analyses indicate that altitude strongly influences the spatial variability of rainy season onset and cessation, particularly in northern and southern regions, whereas latitude plays a significant role in the east. These findings highlight the combined control of topography and geographic location on precipitation responses to general atmospheric circulation. This study demonstrates that the rainy season in Iran reflects a structural spatiotemporal organization. Variations in onset, cessation, and duration correspond with Mediterranean cyclone trajectories, moisture flux convergence, the subtropical jet stream, and regional sea surface temperatures. Overall, the rainy season in Iran is not only a climatic phenomenon but also a manifestation of underlying physical changes in the regional atmosphere–ocean system. | ||
| کلیدواژهها [English] | ||
| Iran, Precipitation, Rainy Season, Spatial analysis, Widespread rainy season | ||
| مراجع | ||
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