Examination of the spatial dispersion and trend of Dust Optical Depth (DOD) in West Asia and its relation with land use change

Document Type : Research Paper

Authors

• Shler Katorani ¹
• Mahmoud Ahmadi ²
• Abbasali Dadashi-Roudbari ³

¹ Ph. D student in Climatology, Faculty of Earth Sciences, Shahid Beheshti University, Tehran,

² Associate professor of Climatology Shahid Beheshti University The Faculty of Earth Sciences Tehran,Iran

³ Postdoctoral Research Associate of Climatology, Department of Geography, Ferdowsi University of Mashhad, Mashhad, Iran

Abstract

Keywords

• Dust trend
• Dust Optical Depth (DOD)
• West Asia
• EAC4 dataset

Main Subjects

• ...

EXTENDED ABSTRACT

Introduction

Global estimates indicate that land use changes and climate change have led to a 40 percent increase in mineral dust. Incorrect traditional farming techniques, rainfed agriculture, and severe, prolonged droughts result in loose soil being exposed to the wind, contributing to the emission of dust from these areas. These conditions cause about 2000 tons of dust to be transported to the atmosphere annually. Although dust is a common climate phenomenon in arid and semi-arid regions, evidence suggests that this event occurs in all climate regions, becoming one of the significant environmental challenges in recent years in the Middle East, particularly in Iran. This study aims to examine the changes in dust in West Asia and its relationship with land use changes. Most studies have confirmed the role of land use and anthropogenic in increasing the event of dust globally and emphasize that a considerable of the emission, transport, and deposition of dust is affected by land use changes and anthropogenic factors. Therefore, identifying and monitoring the Spatio-temporal analysis in dust events and examining the role of land use changes will be essential for preventing this phenomenon.

Materials and Methods

In this research, to examine the monthly trend of dust changes, the Dust Optical Depth (DOD) variable with a horizontal resolution of 0.75o on a monthly scale from the CAMS global reanalysis dataset (EAC4) has been used. Additionally, the global Land Cover Classification System (LCCS) dataset with a horizontal resolution of 300 meters has been utilized to investigate changes in land use. Moreover, the Modified Mann-Kendall test (MMK) has been employed to examine the trend of dust events, and Sen's Slope estimator test (SSE) has been used to assess the trend's slope.

Results and Discussion

The results indicate that the maximum dust optical depth (DOD) occurs in the spring and summer seasons due to decreased soil moisture, reduced river water levels, lack of vegetation cover, and the dry climate in the Mesopotamian regions, the deserts of Iraq and Syria, and southeastern and southwestern Iran. In general, DOD decreases with high latitude in the region; however, in northeastern Iran, due to the presence of the Kyzylkum and Karakum deserts, the Aral Karakum, and Garabogazköl, this index has shown a significant increase. The highest DOD is observed in July in the Mesopotamia region, where the climate average of this index reaches 0.75. The DOD value during the cold period of the year shows an increasing trend in most regions of West Asia, such that in December and January, significant parts of western Iran, central Iran, the south and southeast, and especially in the northeast of the country, the DOD value shows an increasing trend (0.06/decade), which is significant at the 0.05 level. The examination of land use changes has revealed that water bodies have undergone significant changes, including Parishan Lake in Iran, Hamun Lake and Hawizeh Marshes, and the water bodies of Aral Karakum and Garabogazköl in Turkmenistan. Consequently, the drying of rivers and wetlands has led to the emergence of new and active dust sources in this region. Additionally, the regions with dense vegetation cover have decreased from 7.6% to 3.7%, and pastures have decreased from 3.1% to 2.8%, while in contrast, the region of agricultural lands has increased from 16.1% to 16.25%.

Conclusions

The EAC4 dataset has shown high efficiency in examining the spatial distribution of dust, and its results can be used for dust studies. The examination of the DOD trend indicates a significant increasing trend at the 0.05 level in the active dust sources in Iraq (Mesopotamia region), desert regions of Saudi Arabia (Rub' al Khali, Ad-Dahna, Al Nufud deserts), Pakistan (Thar Desert), and Turkmenistan (Kyzylkum, Karakum deserts, the dried bed of Aral Karakum, and Garabogazköl). Notable portions of the land cover in southeastern Iraq and the west and southwest of Iran have been converted to barren lands from 2000 to 2020, and consequently, these regions have experienced the highest amount of dust events. Additionally, the examination of land use has shown that the extent of agricultural lands has increased, while the range of pastures, vegetation covers, and water bodies has decreased. Eroded soils, dried riverbeds, and barren lands have more dust emissions.

Author Contributions

All authors contributed equally to the conceptualization of the article and writing of the original and subsequent drafts.

Data Availability Statement

Data available on request from the authors.

Acknowledgements

The authors would like to thank all participants of the present study.

Ethical considerations

The authors avoided data fabrication, falsification, plagiarism, and misconduct.