Monitoring and analysis of dust storm trajectories in Sistan and Baluchestan Province using MODIS satellite products and the HYSPLIT model

Background and Objective: One of the environmental challenges in arid and semi-arid regions is dust pollution, which can lead to serious health problems, including respiratory diseases, reduced visibility, and disruptions in transportation. Additionally, dust storms have significant negative impacts on water resources and agriculture. Sistan and Baluchestan province is one of the areas that experiences high dust pollution levels annually, with many periods throughout the year showing elevated dust pollution levels.

Materials and Methods: This study utilizes MODIS satellite data and coding in Google Earth Engine to analyze the TDI, AOD-Sum, AOD-Max, and AOD indices from 2018 to 2023. The HYSPLIT model was employed to analyze the transport pathways of dust pollutants and identify their sources. Using particle trajectory modeling techniques, the frequency distribution of closed air paths was examined. To gain a better understanding of dust distribution and transport, true-color MODIS images were also used. For dust trajectory analysis, data from the Zabol and Zahedan stations for three dates in 2023 and 2024, with an AQI index of 500, were employed. The HYSPLIT model was applied in a backward mode with 24-hour trajectories for Zabol and 48-hour trajectories for Zahedan.

Results and Discussion: The analysis of the Thermal Dust Index (TDI) from 2018 to 2023 revealed that areas such as Zabol, Iranshahr, Khash, and Chabahar, due to their dry and loose soils, are the primary internal sources of dust in the province. The TDI increased from 0.0055 in 2018 and 2019 to 0.0058 in 2021, while in 2022 and 2023 it reached 0.0056 and 0.0057, respectively, with a minimum threshold of 0.018. The analysis of the AOD-Max index indicates that the eastern, southern, northeastern, southwestern, and, in some years, the central regions of the province experience the highest levels of dust pollution. Border regions, especially those bordering Afghanistan and Pakistan, have consistently exhibited the highest levels of dust pollution throughout the years. The years 2018 and 2022 recorded the highest values of AOD-Max, with a 0.3-unit increase in 2022 compared to previous years, reaching a value of 3.5, which falls into the "hazardous" category in air pollution classification. This value decreased to 3.1 in 2023 but remained in a "very hazardous" state. The AOD-Sum index analysis shows that the eastern, northeastern, and southern regions of Sistan and Baluchestan experience the highest intensity of dust pollution throughout the year. Particularly, the eastern and northeastern areas face dust pollution for more than 100 days a year, while the southern areas experience it for over 120 days. The highest number of pollution days were observed in 2018, 2020, and 2022. However, the average index value for 2023 decreased by 0.9 compared to 2022, with an average of 1.9, still within the hazardous range. The analysis of AOD indices reveals that the highest pollution is concentrated in the border regions of the province. Moreover, the strong spatial correlation between TDI and AOD values reinforces the validity of these findings and demonstrates that TDI serves as an effective tool for identifying, monitoring, and managing high-risk dust-prone areas. Backward trajectory modeling with the HYSPLIT model shows that, shortly before dust storms occur in Zabol and Zahedan, the air paths predominantly pass through the borders of Turkmenistan and Afghanistan, reaching Zabol and Zahedan. The backward trajectory modeling shows that dust storms originate from the deserts of Turkmenistan and Afghanistan and reach Zabol within 24 hours and Zahedan within 48 hours. The altitude changes of the dust transport pathways indicate that most of the airflows occur at elevations above 1500 meters along the Turkmenistan-Afghanistan border. After passing through the deserts of Afghanistan, the airflow reduces to below 500 meters, causing dust pollution in the province. The true-color MODIS images also clearly show the expansion of pollution from the deserts of Afghanistan and eastern Iran to the borders of Pakistan.

Conclusion: The results show that the eastern and border regions of Sistan and Baluchestan province are most affected by dust storms. These storms, primarily originating from the deserts of neighboring countries Afghanistan, Turkmenistan, and Pakistan—enter the province and exacerbate air pollution. Given the severity of dust pollution in these areas, it is recommended to establish drought-resistant vegetation cover,