تحلیل سینوپتیکی-دینامیکی بارش سنگین منجربه سیل استان گلستان در ماه مارس 2019

نوع مقاله : مقالات پژوهشی

نویسندگان

• فیروز عبدالعلی زاده ¹
• علی محمدخورشیددوست ²

¹ کارشناس هواشناسی سینوپتیک، سازمان هواشناسی کشور

² گروه آب و هواشناسی دانشکده برنامه ریزی و علوم محیطی دانشگاه تبریز تبریز ایران

https://doi.org/10.22067/jsw.2022.78803.1203

چکیده

طی روزهای هفدهم تا بیست و یکم ماه مارس 2019 (26 اسفند 1397 تا 1 فروردین 1398) بارش باران سنگین در استان گلستان (حوضه آبریز گرگانرود) باعث ایجاد سیل و آبگرفتگی در مسیر گرگانرود گردید که خسارات بسیار زیادی به شهرها، روستاها و بخش کشاورزی وارد آورد. لذا در این تحقیق اقدام به بررسی و تجزیه و تحلیل عوامل رخداد سیل مذکور به ویژه عوامل سینوپتیکی-دینامیکی وقوع بارش سنگین، گردید. جهت تحلیل سینوپتیکی-دینامیکی بارش سنگین، با استفاده از منابع داده­ای مختلف (داده­های هواشناسی ایستگاه­های سینوپتیک، پایگاه NCEP/NCAR، محصولات ماهواره MODIS و محصولات ماهواره GPM) ابتدا زمان اوج بارش­ها و شدت بارش مورد شناسایی قرار گرفت و سپس نقشه­های سینوپتیک (نقشه­های ارتفاع ژئوپتانسیل در سطوح میانی و زیرین تروپسفر، چرخندگی نسبی، امگا، سمت و سرعت باد، همگرایی شار رطوبت، تابع جبهه­زایی، رطوبت ویژه جو و نمودار هوف-مولر) تهیه گردیدند و مورد تجزیه و تحلیل قرار گرفتند. نتایج نشان دادند که بارش سنگین از ساعت 18 (به وقت جهانی³) روز هفده مارس شروع شده و تا ساعت 18 روز هجده مارس ادامه داشته است و اوج شدت بارش­ها در روز هجدهم مارس در اکثر ایستگاه­ها بین ساعت­های 06 تا 12 و 12 تا 18 بوده است. بررسی نقشه­های سینوپتیک بیان داشت، منشأ سیستم بارشی تراف عمیق واقع بر بستر موج راسبی می­باشد که در اواخر روز هفدهم مارس به منطقه مورد مطالعه رسیده و باعث شکل­گیری سیکلونی عمیق در این ناحیه شده است و با تزریق رطوبت از آب­های جنوبی ایران و دریای خزر توسط جریانات جوی به داخل سیکلون وقوع بارش­های سنگین را منجر گشته است. از سوی دیگر، توپوگرافی و شیب حوضه شرایط لازم را برای رخداد سیل فراهم آورده است.

کلیدواژه‌ها

• بارش سنگین
• حوضه گرگانرود
• سیل
• همگرایی شار رطوبت

20.1001.1.20084757.1402.37.1.10.9

موضوعات

• هواشناسی کشاورزی

عنوان مقاله [English]

Synoptic-Dynamic Analysis of Heavy Rainfall Leading to Flooding in Golestan Province in March 2019

نویسندگان [English]

• Firooz Abdolalizadeh ¹
• Ali Mohammadkhorshiddoust ²

¹ Meteorologist, Meteorological Organization of Iran

² Department of climatology, Faculty of Planning and Environmental Sciences, University of Tabriz, Tabriz, Iran

چکیده [English]

Introduction
Heavy rains often occur in small areas, but they may be the result of large-scale systems and their energy and moisture are provided from distant areas (Mohamadei et al., 2010). Therefore, identification of synoptic systems is of great importance in order to predict precipitation. Although rain has many positive effects on human life, heavy rain can cause one of the most dangerous and damaging natural disasters, namely floods. Every year, floods cause many human and financial losses in different regions of the world. Floods are more effective in vulnerable areas and cause the loss of human lives, damage to property and products, disruption of transportation and services, and other economic losses (Kheradmand et al., 2018). In March 2019, heavy rains occurred in Golestan province, which caused flooding in parts of this province, especially in the cities of Gonbad-Kavus and Aqqala. Most of this heavy rain and flood occurred in the Gorgan River basin. According to meteorological reports, the rain started from the night of 03.17.2019 and continued until 03.21.2019, although the heaviest rainfall occurred from the 03.18.2019. The volume of the flood was so great that the dams on the Gorgan River could not accommodate it. According to the reports of the regional water company of Golestan province, the flood entered the Bostan dam at 1 am on 03/19/2019, and after passing through it, entered the Vashmgir dam at 6 am, and then on 03.21.2019 entered the city of Aqqala. The damage of this flood was estimated at about 4800 billion Tomans, which includes damage to 17800 residential units, damage to farms, transportation infrastructure, 40% reduction in tourism, damage to industrial units, unemployment of about 3000 people, and damage to the nomads of the province. (Islamic Republic News Agency, 04.09.2019). Considering the heavy damage caused by the mentioned heavy rain and flood in Golestan province, it is necessary to identify and analyze the causes of its occurrence in order to plan and take the necessary measures to prepare and deal with such incidents.
Materials and Methods
The study area is Gorganrood watershed, most of this area is located in Golestan province. Golestan province is one of the northern provinces of the country and is located in the southeast of Caspian sea. In this research, in order to identify and analyze the heavy rain that occurred in Golestan province in March 2019, which led to severe flooding, several types of data were used (data from meteorological stations, NCEP/NCAR reanalyzed data, MODIS satellite images, GPM precipitation products). First, using the rainfall data of the synoptic stations located in the Gorgan River watershed, the time of heavy rainfall was identified, and then using the data of the aforementioned stations and several stations outside the basin, a rainfall zoning map was prepared. MODIS satellite images were also used to check the position of precipitation system and cloudiness of region. Using GPM satellite rainfall products called IMERG, which were extracted on a half-hourly basis, as well as the main synop reports of meteorological stations, which are reported on a six-hourly basis, the intensity of rainfall was investigated. In addition, the physical conditions of the basin were investigated using the topography and slope map of the basin prepared from the DEM layer of the region. In the following, using the reanalyzed data of the NCEP/NCAR database (National Center for Environmental Prediction - National Center for Atmospheric Research of the United States), synoptic maps including maps of land surface pressure, geopotential height of the upper atmosphere, Omega (indicates the speed of vertical movements of the atmosphere), wind direction and speed, moisture flux convergence function, frontal function, specific humidity, atmospheric precipitable water and Hoff-Müller diagram were drawn to identify the synoptic and dynamic factors of the mentioned precipitations.
Results and Discussion
The results of the present research in the analysis of flood factors can be summarized as follows:

Survey of the topography and slope of the Gorganrood basin revealed that the physical conditions of the basin are such that the potential for flooding is high.
The amount of rainfall in 24, 6 and a half hour intervals in the study area were investigated and it was shown that the rainfall occurred on March 17, 18 and 19, especially on March 18, in terms of the intensity of rainfall were very intense.
Investigation of the state of the middle troposphere showed that the formation of the Rossby wave and the meridional expansion of one of its troughs, along with the creation of a positive vorticity that dominated the studied area on the seventeenth of March, are the main factors in the creation of a baroclinic atmosphere and the dynamic ascent of air.
Investigation of the synoptic-dynamic conditions of the lower levels of the troposphere showed that in the lower levels of the low-altitude synoptic system with closed meters, at the same time as the deep trough reigns over the region, it has been formed and strengthened during peak rainfall times and has led to a strong rise of air.
Investigating the state of atmospheric humidity in the study area and identifying sources of moisture supply using special humidity maps, moisture flux convergence function and atmospheric flow paths were carried out.
Investigating the omega variable in the vertical profile of the atmosphere using the Hoff-Mueller diagram showed that during the times of precipitation events, upward movements prevailed in all levels of the troposphere, especially during the peak of precipitation, the upward movements became more intense in the lower levels.
Identifying the type of clouds using MODIS products showed that during heavy rains, especially on March 18, deep convective clouds with a high density of water were formed in the region, which extended up to a height of 300 hectopascals and were very thick.

کلیدواژه‌ها [English]

• Flood
• Gorganrood basin
• Heavy rainfall
• Moisture flux convergence

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