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پژوهش های جغرافیای طبیعی، جلد ۴۵، شماره ۳، صفحات ۱-۱۲
عنوان فارسی تحلیل فضایی خشکسالی های بلندمدت ایران
چکیده فارسی مقاله هدف از انجام این پژوهش، پایش و پهنه‎بندی خشکسالی‎های بلندمدت ایران زمین است. از آنجاکه شاخص بارش استانداردشده (SPI) به تحلیل‎گر امکان می‎دهد تا تعداد وقوع خشکسالی را در مقیاس‎های زمانی مختلف تعیین کند و با برازش خشکسالی‎ها بر تابع چگالی احتمال، تحلیل فراوانی را روی آن انجام دهد، مزیت بهتری برای انتخاب و اجرا دارد. در این پژوهش از داده‎های آماری هفتاد ایستگاهی استفاد شد که دورۀ آماری سی سال به بالا داشتند و با به‎کارگیری نمایۀ SPI در بازه‎های زمانی دوازده و بیست‎وچهارماهه، داده‎ها مورد بررسی و تجزیه‎وتحلیل قرار گرفتند. برای تحلیل فضایی با استفاده از روش‎های زمین‎آمار، نقشه‎های پهنه‎بندی خشکسالی‎ها در محیط ArcGis ترسیم شدند. نتایج پژوهش نشان می‎دهد که در بازه دوازده‎ماهه قسمت‎های شرق، جنوب غرب، غرب و مرکز کشور، خشکسالی‎ها بسیار شدید و شدید است، اما در مناطق شمال شرق، شمال غرب و شمال کشور خشکسالی‎ها متوسط و ملایم است. در بازه بیست‎وچهارماهه غرب، شرق، جنوب شرق، جنوب و مرکز کشور خشکسالی‎ها بسیار شدید و شدید است.
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عنوان انگلیسی Spatial Analysis of Long Duration Droughts in Iran
چکیده انگلیسی مقاله Extended AbstractIntroductionDrought is one of the devastating hazards of human history. It can occur in all times and anyplaces. Drought is a regional event that its occurrence in many world zones cannot be avoided.It is more important than other natural misfortunes due to loss of life and property and socialfactors. This event is more display in arid zones such as Iran for the sake of regionalcharacteristics like small precipitation, intensity in oscillations of rainfall in different years,inappropriate distribution of the rainfall in a period of years and the great fluctuations inplaceand time of the rainfall. For this reason this research has studied the severity and spatialorganization of these droughts over the country.MethodologyImportant parameters that influences drought are temperature and precipitation. In this research,in order to make a spatial analysis of the long duration droughts in Iran, the precipitation datawere used. For this reason the monthly precipitation of 70 long period stations during 1976-2005 were obtained from the Meteorological Organization of Iran.Researchers all over the world offer different methods for study of the droughts. One ofthese is Standardized Precipitation Index (SPI). This method was developed by McKee,Doesken, and Kleist (1993) to analyze the impact of precipitation deficit on groundwater,reservoir storage, soil moisture, snowpack, and stream flow in different time scales for definingand monitoring the phenomenon. These time scales reflect the impact of drought on theavailability of different water resources. Soil moisture conditions respond to precipitation  anomalies in a relatively short time scale. Groundwater, stream flow, and reservoir storagereflect the longer-period precipitation anomalies. For these reasons, McKee et al. (1993)originally calculated the SPI for 3, 6, 12, 24, and 48 months time scales. The SPI computes thetemporal frequency and anomalies of droughts. It can also be used to determine periods ofanomalously wet events. The SPI is recognized as a better quality model compared to othermodels. The advantage of this index is that allows the analyzer to determine the number ofoccurrences of droughts in different stages of time. In the other words, it is, because of the nondistance of this index that we could use of it to compare information of different zones andmake carefully anextent of drought maps. The other advantage of this index is that it ismeasuring the drought function of probable density so that you can perform more analysis aboutthat. The study has used the SPI method for a period of12 and 24 months during the 1976-2005.The spatial distribution of the drought was interpolatedvia ordinary kringingin the ArcGISenvironment.Results and DiscussionIn this study SPI time series were calculated in time scales of 12 and 24 months. Then, thefrequency and spatial distribution of droughts were prepared and analyzed using theGeostatistics methods (Ordinary Kringing). These results have showed that the intensive 12-months period droughts were frequent in the east, southwest, central, and western parts of thecountry ( for example Birjand Station 8%, Ramhormoze Station 6% Ilam Station 5% and SirjanStation 5%), while the southeast and northern parts experienced moderate and weak droughts.But the 24- months droughts were intensive in the eastern parts of the country(for example,Tabass Station 6%,Ramhormoze Station 6%,Iranshahr Station 6%, and Sirjan Station 5%). Thismeans that the longer droughts are common in the east, where they affect the underground waterresources.ConclusionDrought is one of the devastating hazards inhuman histories. The occurrence of the phenomenonis possible in any time and places. Iran as an arid country with fragile climate is prone tofrequent droughts. For this reason this research has studied the severity and spatial organizationof these droughts over the country. The study has used SPI method with the 12 and 24 monthsscales during the 1976-2005 periods. The spatial distribution of the drought was performed viaOrdinary Kringingin the Arc GIS software.The results have indicated that the 12-month period droughts were intensive in the east,southwest, central, and western parts of the country while the southeast and northern partsexperienced moderate and weak droughts. But, the 24- months scale droughts were intensive onthe eastern parts of the country. This indicates that the longer droughts are common in the east,where they affect the underground water resources.
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نویسندگان مقاله ام السلمه بابایی |
استادیار گروه جغرافیا، دانشگاه پیام نور

بهلول علیجانی |
استاد اقلیم‎شناسی، دانشگاه خوارزمی
سازمان اصلی تایید شده: دانشگاه خوارزمی (Kharazami university)

نشانی اینترنتی http://jphgr.ut.ac.ir/article_35831_077ad630608521ab35f862e2327aee11.pdf
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