تحلیل روند مشخصه‌های بارش سالانه و فصلی در ناحیه رویشی هیرکانی

نوع مقاله : مقاله پژوهشی

نویسندگان

1 استاد گروه جنگلداری و اقتصاد جنگل، دانشکده منابع طبیعی دانشگاه تهران

2 داﻧﺸﺠﻮی کارشناسی ارشد ﺟﻨﮕﻞﺷﻨﺎﺳﯽ و اﮐﻮﻟﻮژی ﺟﻨﮕﻞ، ﮔﺮوه ﺟﻨﮕﻞداری و اﻗﺘﺼﺎد ﺟﻨﮕﻞ، داﻧﺸﮑﺪه ﻣﻨﺎﺑﻊ ﻃﺒﯿﻌﯽ، داﻧﺸﮕﺎه تهران

3 داﻧﺸﺠﻮی دﮐﺘﺮای علوم زیستی جنگل، ﮔﺮوه ﺟﻨﮕﻞداری و اﻗﺘﺼﺎد ﺟﻨﮕﻞ، داﻧﺸﮑﺪه ﻣﻨﺎﺑﻊ ﻃﺒﯿﻌﯽ، داﻧﺸﮕﺎه ﺗﻬﺮان

چکیده

این پژوهش با هدف تحلیل روند مشخصه‌های بارش ناحیه رویشی هیرکانی طی دوره سی و سه ساله (2019-1987 یا 1398-1366شمسی) انجام شد. بارش سالانه، فصلی و نیز در دوره‌های یازده ساله (اول (1997-1987)، دوم (2008-1997) و سوم (2019-2008))، هشت ایستگاه هواشناسی همدیدبانی آستارا، رشت، انزلی، رامسر، نوشهر، بابلسر، قائم‌شهر و گرگان تجزیه تحلیل شدند. آزمون ناپارامتری من‌کندال، جهت بررسی روند بارش استفاده شد. در ناحیه هیرکانی، میانگین بارش سالیانه، 1143 میلی-متر، بیشترین در انزلی (1694 میلی‌متر) و کمترین در گرگان (529 میلی‌متر) ثبت شد. آزمون من‌کندال، روند بارش سالیانه را در ایستگاه‌ها و در کل ناحیه رویشی، معنی‌دار نشان نداد (مقدار آماره من کندال: 32/0). بارش در دوره‌های یازده ساله نیز تفاوت ناچیزی داشت (1140 میلی‌متر در دوره اول در مقابل 1146 و 1142 میلی‌متر برای دوره‌های دوم و سوم). بارش و تعداد رخداد سالیانه، همبستگی مثبت و معنی‌داری را در کلیه ایستگاه‌ها نشان دادند (میانگین ضریب همبستگی در ایستگاه‌ها: 58/0). میانگین تعداد رخدادهای بارش سالیانه، 118 رخداد با میانگین اندازه 5/9 میلی‌متر ثبت شد. اندازه رخداد بارش در دوره‌ اخیر، حدود 5/0 میلی‌متر (5 درصد) افزایش نشان داد. در ناحیه هیرکانی، 21 درصد از مقدار بارش سالیانه در طبقه <10 میلی‌متر و 31 درصد، در طبقه >40 میلی‌متر ثبت شد. 34 درصد از بارش سالیانه (383 میلی‌متر) در نیمه اول سال و بیشترین بارش فصلی در پاییز (43 درصد از بارش سالیانه) رخ داد. جوامع گیاهی، اکوسیستم‌های جنگلی و نیز فعالیت‌های کشاورزی در ناحیه رویشی هیرکانی، بشدت متاثر از تغییرات بارش هستند.

کلیدواژه‌ها


عنوان مقاله [English]

Trends analysis of annual and seasonal precipitation characteristics in the Hyrcanian region of northern Iran

نویسندگان [English]

  • Pedram Attarod 1
  • Mahdieh Garoosiha 2
  • Mohammad Javad Mehdikhani 2
  • Samira Beiranvand 3
1 Department of Forestry and Forest Economics, Faculty of Natural Resources, University of Tehran
2 M.Sc. Student of Silviculture and Forest Ecology, Department of Forestry and Forest Economics, Faculty of Natural Resources, University of Tehran
3 Ph.D Student of Forest Biology, Department of Forestry and Forest Economics, Faculty of Natural Resources, University of Tehran
چکیده [English]

We investigated the trend analysis of rainfall characteristics in the Hyrcanian region of northern Iran in a 33-years period (1987 to 2019). Annual, seasonal, and three 11- years periods (1987-1997; 1997-2008; 2008-2019) were analyzed using data recorded at eight synoptic weather stations of Astara, Rasht, Anzali, Ramsar, Noshar, Babolsar, Ghaemshahr, and Gorgan. The Mann–Kendall (MK) non-parametric test was used to determine the rainfall trends. The mean annual rainfall was 1143 mm with the highest and lowest amounts recorded in Anzali (1694 mm) and Gorgan (529 mm), respectively. The MK test demonstrated no significant trends for annual rainfall in each station and the whole region (MK value: 0.32). Rainfall of 11-year periods showed slight differences (1140, 1145, and 1146 mm for the three consecutive periods). Rainfall and the number of annual events per year illustrated positive significant correlations in all weather stations (mean r = 0.58). The mean annual number of rainfall events was 118 with a mean rainfall event of 9.5 mm increased by approximately 0.5 mm (5%) during the recent period. In the Hyrcanian zone, 21% and 31% of the annual rainfall were less than 10 mm and larger than 40 mm, respectively. 34% of yearly rainfall (383 mm) was recorded in the first half of the year and the largest amount of seasonal rainfall was in autumn (43% of total annual rainfall). Plant communities, forest ecosystems, and agricultural activities in the Hyrcanian region will definitely be affected by any change in precipitation.

کلیدواژه‌ها [English]

  • Forest ecosystem
  • Mann– Kendall (MK)
  • Rainfall events
  • Synoptic weather station
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