Geographical Space

fa بررسی وضعیت خشکسالی در استان خراسان رضوی با استفاده از شاخص‌های SPEI و VCI Investigating the drought situation in Razavi Khorasan province using SPEI and VCI indices تخصصي Special پژوهشي Research خشکسالی یک خطر طبیعی است که می تواند اثرات شدید و طولانی مدتی بر سیستمهای طبیعی و انسانی داشته باشد. انتظار می‌رود افزایش گازهای گلخانه‌ای ویژگی‌های خشکسالی را تغییر دهد. لذا برای بررسی خشکسالی استان خراسان رضوی طی دوره 40 ساله از دادههای ایستگاههای هواشناسی سینوپتیک با یک دوره 40 ساله (1980-2020) و یک دوره زمانی 20 ساله (2020-2001) از دادههای سنجنده MODIS ماهواره Terra با تفکیک افقی 1000 متر انجام شد. شاخصهای خشکسالی مورد استفاده شاخص بارش تبخیر-تعرّق استانداردشده (SPEI) و شاخص وضعیت پوشش گیاهی (VCI) است. نتایج نشان داد که خشکسالی استان خرسان رضوی در 40 سال گذشته با شدت و فراوانی بالایی رخ داده است. بالاترین فروانی و شدت خشکسالی در دهه سوم (2010-2001) با بیشینه شدت خشکسالی 69/1- و فراوانی 24/34 درصد به دست آمده است. بررسی شاخص خشکسالی ماهوارهای نشان داد که الگوهای خشکسالی نشان داده شده توسط SPEI و VCI تا حد زیادی موافق هستند. بررسی دههای شدت و فراوانی خشکسالی نشان داد که ویژگی اصلی اقلیمی استان پس از دهه 2000 حرکت به سمت یک اقلیم خشکتر است. مقایسه همزمان این دو شاخص نشان داد که رویدادهای خشکسالی ناشی از بارش (شاخص SPEI) منجر به خشکسالی مبتنی بر پوشش گیاهی در سطح استان نمی‌شوند. همچنین رویدادهای خشکسالی پوششگیاهی (شاخص VCI) به عنوان یک نتیجه از کمبود بارش رخ نمی‌دهند.   Introduction Drought is a natural hazard that can have severe and long-term effects on natural and human systems. An increase in greenhouse gases is expected to change the characteristics of drought. Therefore, it is necessary to have a detailed understanding of drought and its changes at the regional scale. Droughts regularly led to major socio-economic and environmental impacts. Drought is one of the most severe natural hazards, and climate change causes droughts to occur in many regions of the world in the 21st century with a longer period. It is very important to monitor the drought in Razavi Khorasan province and understand its characteristics in the long term. The research results will have many applications in different sectors such as agriculture, water resources, environment, and agriculture. Methods To investigate the drought of the Khorasan Razavi province during a period of 40 years, the data of synoptic meteorological stations with a period of 40 years (1981-2020) have been used. The Spatio-temporal changes of drought the in Khorasan-Razavi province have been done based on the Standardized Precipitation Evapotranspiration Index (SPEI). The Penman-Monteith method has been used to calculate the potential evapotranspiration to calculate the drought. Finally, the frequency and intensity of the drought for the last four decades have been analyzed separately. Also, the VCI drought index, which is a remote-sensing drought index, has been used. This index is calculated using NDVI data from the MODIS sensor. Discussion of Results The results showed that the drought in Khorasan Razavi province has occurred with high intensity and frequency in the last 40 years. The highest frequency and intensity of drought was obtained in the third decade (2001-2010) with the maximum intensity of drought of -1.69 and frequency of 34.24%. A decades-long study of drought severity and frequency showed that the main climate feature of the province after the 2000s was moving towards a drier climate. In general, the potential evapotranspiration in Razavi Khorasan province has an increasing slope from north to south and west to east. The frequency of drought also shows a behavior similar to potential evapotranspiration in Razavi Khorasan province. The highest frequency of drought is seen in the southern and southeastern regions of the province with 26.51%. In other words, more than a quarter of the months of the year in these areas of the province are affected by drought. The simultaneous comparison of SPEI and VCI indices showed that precipitation-induced drought events (SPEI index) do not lead to vegetation-based drought in the province. Also, vegetation drought events (VCI index) do not occur as a result of a lack of precipitation. Conclusions Changes in the characteristics of drought based on the data of the last 40 years, including the frequency, intensity, and areas affected by drought, showed that the droughts of Razavi Khorasan province during the last 40 years show clear decadal changes. Based on the regional changes of drought, several regional differences of drought have been identified. The maximum frequency of drought in the first decade (1981-1990) compared to the fourth decade (2011-2020) has experienced an increase of 11.69%. Analysis of the satellite drought index showed that the drought patterns shown by SPEI and VCI agree to a large extent. the increase in drought in recent years shows that if the concentration of greenhouse gases continues along its current path, the risk of increasing drought-related tensions for natural and human systems in Razavi Khorasan province will increase greatly. Therefore, it is necessary to include programs such as water resources management and cultivation and irrigation calendar in the province-related programs.   خشکسالی, شاخص SPEI, شاخص VCI, سنجنده MODIS, خراسان رضوی. Drought, SPEI index, VCI index, MODIS sensor, Razavi Khorasan. 147 168 http://geographical-space.iau-ahar.ac.ir/browse.php?a_code=A-10-3851-2&slc_lang=fa&sid=1 Mahsan Koroozhdeh مهسان کروژده mahsankoroozhdeh@gmail.com 100319475328460023390 100319475328460023390 No Doctoral student of Climatology, Department of Geography, Ahar Branch, Islamic Azad University - Ahar-Iran. دانشجوی دکتری رشته آب و هواشناسی، واحد اهر، دانشگاه آزاد اسلامی، اهر، ایران karim Amininia کریم امینی نیا karimaminini@gmail.com 100319475328460023391 100319475328460023391 Yes Department of Geography, Ahar Branch, Islamic Azad University - Ahar-Iran. گروه جغرافیا، واحد اهر، دانشگاه آزاد اسلامی، اهر - ایران Mehdi Saghebian سیدمهدی ثاقبیان smsaghebian@gmail.com 100319475328460023392 100319475328460023392 No Department of Civil Engineerin, Ahar Branch, Islamic Azad University - Ahar - Iran گروه عمران، دانشکده فنی و مهندسی، واحد اهر، دانشگاه آزاد اسلامی، اهر - ایران