Spatiotemporal Monitoring and Analysis of Snow Cover and Its Related Components in the Alborz Mountain Range

Articles in Press

Document Type : Research Article

Author

• Vahid Safarian

Assistant Professor in Climatology, Department of Climatology, Faculty of Natural Resources, University of Kurdistan, Sanandaj, Iran

10.22067/geoeh.2025.94771.1601

Abstract

This study aimed to analyze the temporal and spatial patterns of snow cover in the Alborz Mountains during the cold months, from December to April, over the period 2001–2024. Satellite data from the MODIS sensor and the FLDAS model were utilized within the Google Earth Engine platform, and the Normalized Difference Snow Index (NDSI) was applied to monitor snow cover. Additionally, snow depth, snow water equivalent, and instantaneous snowfall rate were estimated and analyzed. The results showed that maximum snow cover was generally observed in January and February, with 2008 exhibiting the largest snow-covered area across all temporal scales (daily, monthly, and annual). In contrast, 2012 recorded the highest values for snow depth (21.70 cm), snow water equivalent (4.96 cm), and instantaneous snowfall rate (0.058 mm/h), indicating that intense snowfall events were concentrated in more localized areas that year. Temporal patterns were analyzed using a linear regression model, with coefficients of determination (R²) of 0.037, 0.038, and 0.007 reported for snow depth, snow water equivalent, and instantaneous snowfall rate, respectively. These generally low values suggest that seasonal variability and atmospheric conditions play a more significant role than temporal trends in driving fluctuations in snow storage. Spatial assessments further indicated that the western, central, and northern highlands of the Alborz Mountains exhibited the highest snow accumulation, whereas the southern slopes, due to lower elevations and higher temperatures, displayed more scattered snow cover. This study highlights the importance of simultaneously monitoring multiple snow-related variables to improve understanding of winter water resources and underscores the implications of climate change in Iran’s mountainous regions.




Introduction
Snow is one of the primary sources of streamflow in many regions, and an accurate understanding of its temporal and spatial patterns is essential for the optimal management of limited water resources (Soleimani et al., 2018: 77). Variations in snow cover especially in areas with high spatial heterogeneity have significant impacts on ecosystem structure, soil characteristics, and vegetation diversity (Faraji et al., 2024: 161). Given that snow is a key source of freshwater in many parts of the world, its continuous and precise monitoring holds particular importance in water resource studies (Ahmadi & Seyedmirzaei, 2022: 59). This study seeks to identify snow cover trends across different time intervals through the analysis of satellite data and related modeling approaches.
Material and Methods
The aim of this study was to examine the temporal and spatial variations in snow cover and its associated parameters including snow depth, snow water equivalent (SWE), and instantaneous snowfall rate across the Iranian sector of the Alborz Mountain Range during the cold months (December, January, February, March, and April) from 2001 to 2024. To this end, daily remote sensing data (MODIS product) were used for NDSI, and modeled data from the FLDAS dataset were utilized for snow-related variables. Data processing was carried out using JavaScript within the Google Earth Engine environment, and statistical analyses were performed in Python.
Results and Discussion
The findings of this study regarding snow-covered area at three temporal scales daily, monthly average, and annual (with temporal uniqueness) indicate significant variability. At the daily scale, the largest snow-covered areas occurred on a few specific days within the study period. These days and their corresponding snow-covered extents are as follows: the highest snow-covered area was observed on February 6, 2008, with 197,478.188 km²; followed by January 17, 2006, with 152,740.51 km²; and January 30, 2001, with 139,546.354 km². At the monthly average scale, the greatest snow-covered area was recorded in January, reaching 244,161.867 km². At the annual scale (based on temporal uniqueness), the year 2008 had the maximum snow-covered area of 343,435.132 km², while the minimum was observed in 2010, with an area of 138,759.11 km². However, the analysis of the three parameters average snow depth, average snow water equivalent, and average snowfall intensity rate indicates that their highest values were recorded on specific winter days. The maximum average snow depth was observed on February 1, 2012, with a value of 21.70 cm; the highest average snow water equivalent was also recorded on the same day, at 4.96 cm; and the peak average instantaneous snowfall rate reached 0.058 mm per hour on February 1, 2012. The coefficients of determination (R²) for temporal trends were low (ranging from 0.007 to 0.038), suggesting a weak role of time in explaining snow variability and emphasizing the importance of atmospheric, seasonal, and spatial factors.
Conclusions
The analysis of snow cover in the Alborz Mountain Range over the period 2001 to 2024, using daily, monthly, and annual data, revealed that snow variations do not follow a uniform pattern and have experienced significant fluctuations over time. At the annual scale, 2008 and 2010 were identified as notable years, with the highest and lowest snow-covered areas, respectively. Meanwhile, at daily and monthly scales, the greatest snow cover predominantly occurred in January and February, reflecting the concentration of snowfall during the winter season. Furthermore, the analysis of three key snow-related variables snow depth, snow water equivalent, and instantaneous snowfall rate revealed that their highest values were recorded in 2012. This indicates that the intensity and physical characteristics of snowfall in that year were notably significant, even though the snow-covered area was smaller compared to 2008. This discrepancy highlights the importance of a comprehensive, multifaceted examination of both qualitative and quantitative snow parameters. Although the snow-covered area peaked in 2008, the snow depth, snow water equivalent, and instantaneous snowfall intensity were notably higher in 2012. This discrepancy is likely attributable to variations in the spatial distribution and intensity of snowfall. Statistical analyses and descriptive charts also indicate that the data distribution is right-skewed, with outliers observed primarily in the cold months, especially January and February. Positive correlations exist between snow depth and both snow water equivalent and snowfall rate, while these variables show a negative correlation with the progression of the months throughout the year, reflecting a gradual decline in snow characteristics during the warmer seasons.

Keywords

• Snow
• NDSI
• MODIS
• FLDAS
• Alborz Mountain Range

Main Subjects

• Climatic and atmospheric hazards

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©2025 The author(s). This is an open access article distributed under Creative Commons Attribution 4.0 International License (CC BY 4.0)

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