تحلیل مکانی و زمانی شاخص خشکسالی pdi در منطقۀ شمال ‌غرب ایران

خشکسالی از مهم‌ترین پدیده‌های اقلیمی است که مخاطرات و پیامدهای زیادی برای انسان و محیط‌زیست دارد. در این پژوهش، از داده‌های دما و بارندگی 20 ایستگاه سینوپتیک شمال‌ غرب ایران در دورۀ آماری 35 ساله (2021-1987) به‌منظور استخراج و تحلیل روند شاخص خشکسالی pdi و مقایسۀ آن با شاخص‌های spi و spei استفاده شد. نتایج نشان داد براساس شاخص pdi، حدود 85% ایستگاه‌ها، روند صعودی و 15% ایستگاه‌ها، روند نزولی دارند. ازلحاظ تغییرات مکانی ایستگاه مراغه، تبریز، سراب، سقز، خوی، ماکو و خلخال دارای بیشترین خشکسالی، و ایستگاه‌های خرمدره، سنندج، زنجان، تکاب، بیجار و جلفا دارای کمترین خشکسالی سالانه بوده است. علاوه‌بر‌ این، بیشترین دورۀ ترسالی در ایستگاه بیجار و طولانی‌ترین دورۀ خشکسالی در ایستگاه اردبیل مشاهده شد. در بازۀ زمانی 1991 تا 1994 تقریباً تمام ایستگاه‎های مورد مطالعه، شرایط ترسالی داشتند. پس از 1998 تقریباً تعداد ایستگاه‌های با شرایط خشکسالی، افزایش داشت و در بازۀ زمانی 2012 تا 2017 بیشتر ایستگاه‌ها، خشکسالی را تجربه کردند. نتایج نشان داد همبستگی بالایی بین شاخص pdi و شاخص‌های متداول خشکسالی spi و spei وجود دارد. از شاخص pdi به‌دلیل محاسبۀ آسان و مستقل بودن آن از پارامترهای آماری، در تحلیل خشکسالی استفاده شد.

spatial and temporal analysis of pdi drought index in the northwest zone of iran

introduction: drought stands as an inevitable natural disaster with no means of prevention. its detrimental impacts extend across diverse sectors, including water resources, agriculture, and the environment. drought is typically defined as a substantial scarcity of natural freshwater resources persisting over an extended period due to shifts in precipitation and temperature patterns. consequently, periods marked by below-average rainfall often result in temporary drought, particularly in arid and semi-arid regions characterized by relatively high temperatures. globally, drought events are classified into four categories: meteorological, soil moisture (agricultural), hydrological, and socio-economic. studying drought becomes imperative for implementing optimal solutions and strategies to manage water resources and ensure food security, among other concerns. materials and methods: this research utilizes the pedj drought index (pdi), a unique and potent tool, to delve into drought analysis. the pdi, grounded in precipitation and temperature data, offers a more accurate and accessible understanding of drought’s spatial and temporal characteristics. based on yearly averages at stations, this innovative approach provides a fresh perspective on drought analysis. we gathered and scrutinized annual rainfall and temperature data from 20 synoptic stations in northwestern iran from 1987 to 2021 to conduct this study. the pdi’s accuracy and accessibility make it a reliable choice for drought analysis, providing a comprehensive view of the situation. results: from 1991 to 1995, most of the studied stations experienced wet conditions, while from 2013 to 2017, they faced a severe drought. the most extended wet period occurred in the south at the bijar station (9 years), and the most prolonged drought period happened in the east at the ardabil station (8 years). the maximum wet period based on the pdi index (9 years) was observed at the bijar station, and the most prolonged drought period was at the ardabil station (8 years). in the northwest of the country, the average duration of the most extended wet periods is 5.5 years, and the average duration of the most prolonged drought periods is 7.5 years. additionally, the central station experienced two 5-year drought periods, and the tabriz station underwent two 4-year wet periods. based on the precipitation anomaly index, 60% of the stations (12 stations) showed a decreasing trend in precipitation anomalies, with the sanandaj and maragheh stations having a significant 95% decrease. in comparison, only 40% (8 stations) exhibited an insignificant upward trend in precipitation. the temperature anomaly index showed an upward trend in all studied stations, with only bijar, takab, sarab, and miandoab stations (highlighted in red) having a significant 95% increase. according to the drought index pdi, none of the stations experienced extremely dry (exd) or moderately dry (mid) conditions.