خوشه‌های مکانی و روند تغییرات نواحی هم رخداد خشکسالی در ایران

Introduction

Drought 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.



Materials and Methods

The 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 Iran

To 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 Discussion

Annual 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 different seasons of the year. For example, in summer, despite reduced precipitation in the northern and southeastern regions, the number of drought clusters increases, possibly due to occasional and scattered convective rainfall. In contrast, in fall, spring, and even summer, the seasonal drought regions expand along the geographical length, with significant differences in the northwest, which is divided into two regions in fall and expands widely in winter, covering the northern part of Zagros and the western part of the Caspian Sea and Zagros in spring.

In the analysis of seasonal drought changes in Iran, an overall increase in winter drought and a decrease in fall drought are observed. This trend is associated with significant changes in different regions of Iran. Southern Iran, southwestern Iran, and the northern half of the central plateau are experiencing a decrease in fall drought. Conversely, an increase in winter drought is observed in Kerman-east and northeastern regions of Iran. In spring, changes in seasonal drought are observed, but these changes are not significant and have occurred in two regions: the southwest Zagros in southern and central Iran. Analyses propose that these changes may be due to changes in atmospheric circulation and increased atmospheric moisture during this season. Spatial maps illustrating the monthly occurrence of drought clusters show significant differences across various geographical regions throughout the year. This diversity escalates from a minimum of six regions during consecutive cold months to nine regions during two consecutive warm months. Geographical features, such as the Zagros and Alborz mountain ranges, are implicated in shaping monthly drought clusters, particularly during months such as October, December, April, and May.

While analyzing the changes in extent of drought across Iran's different regions, a noticeable pattern observed throughout the year. In January, drought extent notably increases in the northeast and east of Iran and along the Caspian Sea coasts. While the increase in drought extent is not significant in the central plains and the southern coasts up to the eastern border. In November, this pattern reverses, with a more pronounced reduction in extent of drought observed in the central plains and southern coasts extending to the eastern border. In March and April, an increase in drought extent evident in the central, eastern, northeastern, and southwestern regions, while a significant decrease is observed in southeastern Iran. The observed pattern indicates that monthly changes in drought in Iran are related to increased precipitation variability and changes in precipitation patterns throughout the year.



Conclusion

This study pursued two primary objectives. Firstly, it employed spatial clustering at monthly, seasonal, and annual scales to delineate regions experiencing concurrent drought conditions. The findings revealed a spatial and temporal alignment of drought patterns in Iran with its geographical and climatic attributes The emergence of spatial clusters with different drought behaviors at varying times suggests that the influence of changes in atmospheric circulation and precipitation systems outweighs geographical constancy. Notably, while discrepancies in the patterns of monthly and seasonal drought variations do not significantly reflect the annual changes, this feature becomes a distinctive characteristic of the drought variation pattern in Iran. Such differences may be due to changes in the atmospheric circulation pattern and the activity of precipitation systems. Ultimately, the transition in precipitation regimes, characterized by a decrease in the average number of rainy days and an increase in precipitation intensity, underscores to future climate challenges in Iran. These challenges could profoundly impact the region's water resources and economy.