تحلیل طوفان های گردوغبار سیستان با استفاده از شاخص های DDI و DSI و پارامترهای سرعت باد، دید افقی و غلظت PM10

نوع مقاله : مقاله کامل علمی پژوهشی

نویسنده

گروه مرتع و آبخیزداری، دانشکده آب و خاک، دانشگاه زابل

چکیده

سابقه و هدف: در طی دهه های اخیر طوفان های گردوغبار به یکی از مخاطرات جدی طبیعی در دنیا تبدیل شده اند. اگر چه این پدیده از جنبه های مختلف مورد مطالعه قرار گرفته است، تغییرات لحظه ای پارامترهای مرتبط با این پدیده و همچنین تغییرات فراوانی ماهانه و سالانه این پدیده در مناطق تحت تاثیر نیاز به بررسی دارد. از اینرو در این تحقیق تغییرات لحظه ای سرعت باد و دید افقی در طی شبانه روز، ماه های مختلف سال و همچنین تغییرات فراوانی ماهانه و سالانه طوفان های گردوغبار در منطقه سیستان مورد مطالعه قرار گرفت.
مواد و روش ها: منطقه سیستان در جنوب شرق ایران به عنوان منطقه مورد مطالعه در نظر گرفته شد. این منطقه دارای اقلیم گرم و خشک، متوسط بارندگی سالانه کم (59 میلیمتر) درجه حرارت بالا (میانگین سالانه 22 درجه سانتیگراد) و بادهای 120 روزه می باشد. جهت بررسی تغییرات لحظه ای سرعت باد و دید افقی داده های ثبت شده در مقیاس زمانی سه ساعته در ایستگاه سینوپتیک زابل از سازمان هواشناسی کشور برای بازه زمانی 1370-1397 دریافت گردید. همچنین جهت بررسی تغییرات فراوانی طوفان های گردوغبار وغبارناکی منطقه مورد مطالعه از دو شاخص DDI (روزهایی که سرعت باد بیشتر از 15 متر بر ثانیه و دید افقی کمتر از 1000 متر می باشد) و DSI (شاخص غبارناکی) استفاده شد. تغییرات روزانه، ماهانه و سالانه PM10 (ذرات معلق در هوا با قطر کمتر از 10 میکرون) نیز در بازه زمانی 1392-1397 مورد بررسی قرار گرفت.
یافته ها: الگوی تغییرات لحظه ای باد و دید افقی و همچنین غلظت PM10 در طی شبانه روز در تمامی ماه های سال و در بازه زمانی مورد برسی یکسان بوده و حداکثر غلظت PM10 و حداقل دید افقی در ساعت 10:30 صبح منطبق با حداکثر سرعت باد رخ می دهد. همچنین در ساعت 7:30 بعدازظهر منطبق با به حداقل رسیدن سرعت باد و غلظت PM10 میزان دید افقی به حداکثر میرسد. فراوانی ماهانه شاخص های DDI و DSI و همچنین غلظت PM10 نشان داد که ماه تیر بالاترین مقادیر این شاخص ها یعنی 8DDI = روز، 15 DSI = روز و662 PM10 = میکروگرم در مترمکعب را دارا می باشد. در طول دوره مورد بررسی سال 1380 با 31860 دقیقه (531 ساعت) زمان طوفانی و دارا بودن شاخص 74DDI = روز از بالاترین فراوانی این پدیده برخوردار بوده است. بطور کلی بازه زمانی 1378-1383 از شرایط غبارکی شدیدتری نسبت به بازه های زمانی 1370-1377 و 1384-1397 برخوردار می باشد. در این بازه های زمانی شاخص DSI بترتیب 14، 174 و 66 روز برآورد گردیده است. ارتباط معنی دار بین تغییرات سرعت باد و دید افقی، بین سرعت باد و غلظت مواد معلق در هوا و بین دید افقی و غلظت مواد معلق در هوا نشان داد که میزان دید افقی و غلظت مواد معلق در هوا کاملا به سرعت باد وابسته می باشد. همچنین ارتباط معنی داری بین غلظت مواد معلق در هوا (PM10) با شاخص های DDI و DSI نیز برقرار گردید. با برقراری ارتبط بین شاخص های DDI، DSI، PM10 و متوسط سالانه سرعت باد مشخص گردید که تغییرات این پارمترها نیز کاملا وابسته به تغییرات سرعت باد می باشد.
نتیجه گیری: در بازه زمانی 27 ساله مورد بررسی شرایط غبارناکی بر منطقه سیستان حاکم بوده و در مقایسه با سایر مناطق ایران از وضعیت بحرانی تری از غبارناکی برخوردار می باشد بطوریکه فراوانی و شدت طوفان های گردوغبار در این منطقه نسبت به سایر مناطق بیشتر می باشد. از آنجاییکه غبارناکی منطقه سیستان به وضعیت دریاچه هامون مرتبط است بنظر می رسد بهترین راه جهت کاهش طوفان های گردوغبار احیای این دریاچه بوده تا بتوان شرایط تشکیل این پدیده را به حداقل رساند.

کلیدواژه‌ها

عنوان مقاله [English]

Dust storms analysis in the Sistan region using DDI and DSI indices and wind speed, visibility and PM10 parameters

نویسنده [English]

  • Abbas Miri
Department o f Range and Watershed Management, Faculty of Soil and Water, University of Zabol, Zabol, Iran
چکیده [English]

Background and objectives: In the recent decades dust storms have become serious natural hazards in the world. Although dust storms have been investigated in various aspects variation in wind speed and visibility and the frequency of dust storms requires more investigation. In this study, diurnal, monthly and yearly variation of parameters including wind speed, visibility and PM10 (particulate matter 10 micrometers or less in diameter) and frequency of dust storms is studied in the Sistan region for the twenty seven-year period.
Materials and methods: The Sistan in the southeast part of Iran is considered as the study area. Sistan has an arid and semi-arid climate with very low precipitation (59 mm) and air humidity and high evaporation (nearly 4820 mm) and annual temperature (22°C). To analysis the diurnal, monthly and yearly variation of wind speed and visibility, the collected data at the Zabol meteorological station were obtained from the Iran Meteorological Organization for study period. DDI (Dusty Days Index; the days with wind speed more than 15 m/s and visibility less than 1000 m) and DSI (Dusty Index) were applied in this study to analysis the monthly and yearly frequency of dust storms during 1991-2018. Furthermore, the hourly concentration of PM10 was received from the meteorological and environmental stations of the respective centers during 2013-2018.
Results: The results show similar diurnal, monthly and yearly patterns of wind speed, visibility and PM10 variation in all months during study period. The highest PM10 concentration and lowest visibility were observed at 10:30 am in accords with highest wind speed. The lowest PM10 and highest visibility occurred at 7:30 pm in accord with lowest wind speed. The greatest values of DDI, DSI and PM10 were observed in June. Furthermore, the greatest values of DDI, DSI and PM10 were observed in 2001 during study period. The period of 1999-2004 is dusty than the periods of 1990-1999 and 2005-2018 as DSI is 14, 174 and 66 days respectively. A strong correlation was observed between wind speed and visibility, wind speed and PM10 concentration and, visibility and PM10. These result show that either PM10 concentration or visibility depend on wind speed. Furthermore, a positive relationship was observed between PM10 and DSI and DDI.
Conclusion: In stud period, the Sistan region is dusty than other regions of Iran due to having greater frequency and intensity of dust storm. As the dustiness of Sistan is highly dependent on the situation of Hamoun lake, lake recovery is critical to reduce the intensity and frequency of dust storms.

کلیدواژه‌ها [English]

  • Dust storms
  • Wind speed
  • Visibility
  • Sistan

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مجله پژوهش‌های حفاظت آب و خاک
دوره 27، شماره 1
فروردین و اردیبهشت 1399
صفحه 1-23

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