Extended Abstract:
Introduction
Dust storms, a significant environmental challenge in arid and semi-arid regions, profoundly impact air quality, public health, ecosystems, and economies. Golestan Province, located in northern Iran, is vulnerable to dust storms due to its proximity to the Caspian Sea, Turkmenistan’s deserts, and diverse land cover, including Hyrcanian forests, wetlands, and extensive croplands. Elevated concentrations of PM10 and PM2.5, particularly during dry seasons, exacerbate respiratory and cardiovascular issues, imposing substantial economic burdens on healthcare systems. Dust sources include local bare lands and transboundary inputs from Turkmenistan’s deserts, transported by seasonal winds. Dust accumulation threatens ecosystems such as the Hyrcanian forests by reducing photosynthesis and biodiversity. Additionally, the Caspian Sea’s receding water levels and drying margins have created new dust hotspots. Land-use changes, such as deforestation for agriculture, have intensified these effects. Aerosol Optical Depth (AOD) serves as a critical indicator of suspended particle concentration, influencing Earth’s radiative balance and precipitation patterns through light absorption and scattering. Climatic factors (e.g., reduced soil moisture and vegetation) and anthropogenic activities (e.g., unsustainable agriculture and lake desiccation) drive AOD increases in arid regions. This study aims to analyze the seasonal and spatial patterns of AOD in Golestan, identify dust sources, and evaluate the roles of land cover and climatic conditions. Leveraging satellite data and spatiotemporal analysis, it seeks to detect emerging hotspots and propose management strategies.
Data and Methodology
To monitor dust events from 2001 to 2024, daily MOD08_D3 data from the MODIS sensor at 550 nm wavelength with 1000-meter spatial resolution were retrieved from Google Earth Engine, employing the Deep Blue algorithm. AOD thresholds (0.3, 0.4, 0.5, and 0.6) were evaluated, with 0/5 validated as optimal for detecting significant dust events while minimizing atmospheric noise, confirmed using synoptic station data from Gorgan, Hashemabad, Maravetappeh, Kalaleh, Gonbad, and Incheboroun. Maximum AOD intensities within 1, 5, and 10 km radii of stations were extracted, supporting the 0.5 threshold. Land cover analysis utilized the Dynamic World V1 product from Sentinel-2 (10 m resolution), comprising nine classes (bare land, cropland, forest, salt flats, water, urban, rangeland, wetland, snow/ice). Data for 2024 were extracted to assess seasonal land cover changes and their relation to AOD frequency. AOD values were categorized into four quartile classes to examine spatiotemporal patterns. The Overlay Raster (Combine) function in ArcGIS Pro was used to integrate land cover and AOD data, identifying unique combinations. Spatiotemporal analyses were conducted using the Space Time Pattern Mining module in ArcGIS Pro. Seasonal AOD data were converted into a space-time cube, and EHSA, employing the Getis-Ord Gi* statistic, identified hot and cold clusters. Parameters included the K_NEAREST_NEIGHBORS method (8 neighbors), annual time steps, and a 1 km neighborhood distance. The Mann-Kendall test analyzed temporal AOD trends, detecting significant increasing or decreasing trends at 90%, 95%, and 99% confidence levels.
Results
Summer emerged as the most critical season for dust events, with 51% of the province in high-frequency classes (>21.471 days), driven by high temperatures, low soil moisture, and local winds. Spring and autumn showed moderate to high activity (50.4% and 52% in mid-to-high frequency classes, respectively), while winter had minimal activity (89.59% dust-free), attributed to high precipitation and humidity. Spatially, dust events concentrated in northern and eastern bare lands. Land cover analysis for 2024 revealed bare lands as the dominant aerosol source, covering 48.85% in summer and 43.76% in spring. Croplands peaked in winter (36.66%) and spring (27.48%), declining to 22.06% in summer. Forests were most extensive in summer (18.79%) and autumn (18.18%), reducing to 10.1% in winter. Snow (15.35% in winter) and water/wetland covers were prominent in colder seasons, reflecting climatic and agricultural influences. Bare lands, particularly in high AOD classes (up to 21.97% in spring, 21.59% in summer), were the primary aerosol sources. Vegetative covers (forests, croplands) reduced AOD in lower classes but were less effective in severe dust conditions. Agricultural activities, such as plowing in spring and autumn, increased AOD in croplands. Urban areas had a minimal role in aerosol production. EHSA showed summer with the largest hotspot coverage (4785 km², mostly sporadic at 4274 km²), followed by autumn (3552 km²) and spring (2878 km²). Winter had the least (384 km²). New hotspots were prominent in autumn (428 km²) and summer (315 km²), indicating dynamic dust sources. Intensifying hotspots appeared in winter and spring, while persistent hotspots were notable in autumn. No cold spots were identified, likely due to overall aerosol increases or analysis constraints. The Mann-Kendall test indicated AOD stability across >90% of the province, with significant increasing trends in autumn (4.38%, 95% confidence) and summer (1.90%, 90% confidence), concentrated in central and Caspian coastal areas. Decreasing trends (<0.5%) were limited to Alborz forested margins.
Discussion and Conclusion
Summer’s dry conditions and strong winds make it the most critical season for dust events, with bare lands in northern and eastern Golestan as primary aerosol sources, consistent with regional studies. Vegetative covers mitigate AOD in non-critical conditions but are limited during severe dust events. EHSA highlighted widespread hotspots in summer and new hotspots in autumn, linked to Caspian Sea level decline and land-use changes. The Mann-Kendall test confirmed long-term AOD stability, with localized increases in autumn and summer, necessitating targeted management. This study underscores the influence of land cover, climate, and human activities on AOD patterns. Restoration of vegetative cover, sustainable agricultural practices, and continuous remote sensing monitoring are recommended to mitigate dust impacts, enhancing natural resource management and reducing health and economic consequences in Golestan.