خوشه‌های مکانی و روند تغییرات نواحی هم رخداد خشکسالی در ایران

بی‌هنجاری‌های بارشی به‌ویژه خشکسالی و تغییرات آن از مورد توجه‌ترین موضوعات اقلیم‌شناسی است. مطالعه حاضر باهدف ناحیه‌بندی رخدادهای خشکسالی و ارزیابی روند تغییرات گستره آن در مقیاس‌های زمانی سالانه، فصلی و ماهانه انجام پذیرفت. به این منظور از داده‌های بارش ماهانه ear5 و شاخص خشکسالی rai بهره گرفته شد. برای استخراج خوشه‌های مکانی و روند تغییرات آنها، از تحلیل خوشه‌ای سلسله مراتبی مبتنی بر فاصله همبستگی - ادغام وارد و آزمون من‌کندال و شیب‌خط رگرسیونی استفاده گردید. تعداد خوشه‌های مکانی (نواحی) هم‌رخداد خشکسالی در فصل و ماه‌های بارشی نسبت به ماه‌های کم‌بارش مانند فصل تابستان، وسیع‌ و همگن‌‌تر است. نواحی مشخص جغرافیایی -اقلیمی مانند: جنوب شرق، مرکز، شمال غرب و غرب -جنوب غرب، در بیشتر زمان‌ها دیده می‌شود. تغییرات خشکسالی سالانه در هیچ یک از نواحی روند معنی‌داری نشان نمی‌دهد که این می‌تواند از تضاد درون فصلی و ماهانه در روند تغییرات خشکسالی باشد. به‌طوری‌که در فصل زمستان و بهار (دوره اصلی بارش کشور) روند افزایشی و در مقابل در فصل پاییز، روندی کاهشی خشکسالی مشاهده شد. در مقیاس ماهانه نیز مشهودترین روند افزایشی در دو ماه اصلی بارش کشور یعنی ژانویه، مارس و کاهشی در ماه نوامبر رخ‌داده است. نتایج پژوهش می‌تواند گویای جابه‌جایی زمانی بارش یا تغییر رژیم بارش کشور باشد

spatial clusters and trends of change in drought co-occurrence regions in iran

abstractprecipitation anomalies, especially drought and its changes are among the most important topics in climatology. the current study was carried out to regionalize drought events and evaluate the changes in their extent in annual, seasonal and monthly time scales. for this purpose, ear5 monthly rainfall data and the rai drought index were used. hierarchical cluster analysis based on ward’s correlation-integration distance mann-kendall’s test and the slope of the regression line were used to extract spatial clusters and their changes. the number of spatial clusters (areas) of co-occurrence of drought in the rainy season and months is wider and more homogeneous than in the less rainy months such as the summer season. certain geographical-climatic areas such as southeast, center, northwest and west-southwest are seen most of the time. the annual drought changes in none of the areas show a significant trend, which could be due to intra-seasonal and monthly contrasts in drought changes. so in winter and spring (the main rainfall period of the country), an increasing trend was observed, and on the other hand, in autumn, a decreasing trend of drought was observed. on a monthly scale, the most obvious increase trend has occurred in the two main months of rainfall in the country, namely january and march, and a decrease in november. the results of the research can indicate the temporal shift of rainfall or the change in the country’s rainfall regimeextended abstractintroductiondrought is a global challenge with profound economic, social and environmental impacts. the amalgamation of climate change and socio-economic dynamics has exacerbated the frequency and severity of drought occurrences. delving into the nexus of these factors and scrutinizing the temporal variability of drought as a fundamental priority has fostering advancements in drought management, forecasting and the quest for efficacious solutions.iran is a country that constantly confronting the challenges of drought. numerous research underscores the variegated precipitation oscillations and drought intensities pervading different regions of iran.in addition, investigations into the environmental and agriculture repercussions of drought have been conducted, with scholars endeavoring to forecasting future drought trends through forecasting and simulation models. the introduction of drought indicators, modification, and development of methods for drought assessment are of great importance for the management of this phenomenon. resource optimization and crafting adaptive strategies tailored to the drought patterns across disparate regions can hold promise in surmounting this challenge. moreover, an incisive assessment of drought risks is imperative for the codification of preemptive policies and the efficacious management of this phenomenon.however, further research is needed on the temporal and spatial variability of drought. while extant research, has gravitated towards regionalization and impact of drought risks the spatial stability across divergent timeframes remains inadequately explored. studying spatial clustering elucidating homogeneous drought patterns can significantly improve drought forecasting, warning and management processes. this challenge propelling researchers towards novel inquiries and innovative solutions in the realm of drought dynamics. methodologythe scope of research is iran’s expansive terrain, from the zagros and alborz mountain ranges to the vast internal plains and coastal margins of the persian gulf, the oman sea in the south and the caspian sea in the north. the extensive environmental diversity, resulting from the country’s complex topography, engender a significant difference in the spatial and temporal patterns of precipitation among different regions. different precipitation patterns and spatial changes along with temporal changes lead to phenomena such as drought, heavy rains and floods in iranto study the spatial and temporal patterns of precipitation in iran, era5 data have been used as a new and powerful data source. in pursuit of comprehending iran’s spatial and temporal patterns of precipitation, era5 data have been used as a new and powerful data source. these data are from the ecmwf database and have high spatial accuracy and different time intervals. prior research has shown that these databases considered as a robust and dependable source for precipitation-related studies in iran. by utilizing this database, this investigation explore drought patterns, identifying co-occurring drought clusters analysis using drought indices. furthermore, cluster analysis is used to examine spatial clusters of drought at annual, seasonal, and monthly scales, and to assess changes in drought extent within each cluster. results and discussionannual drought clusters in iran, delineating seven different spatial clusters that are associated with different geographical and climatic features, including topography, geographical latitude, and precipitation system trajectories. these clusters include different regions from the caspian sea’s southern coast to the central plains and deserts, the northern zagros and foothills, the southwest from the persian gulf coasts to the foothills of the central zagros, and the southeast and east. these clusters indicate the simultaneous occurrence of annual droughts, with notable regional differences, especially along the caspian sea, where variations between the western and northwestern regions, as well as the western and southwestern regions, are evident.analyses proffers discernible disparities in the magnitude of drought changes within these annual clusters. while the central region and the southern coasts of the caspian sea show a decreasing trend, the central plains and deserts show increasing trends underscoring the disparate climatic and geographical influences. furthermore, seasonal cluster analysis indicates that different seasonal drought regions are observed in iran during