Spatial Analysis of Snow Cover in Western Iran Using Satellite Imagery

آب و خاک

Article 10, Volume 38, Issue 1 - Serial Number 93, March and April 2024, Pages 161-173   

Document Type: Research Article

DOI: 10.22067/jsw.2024.83893.1323

Authors

A. Faraji¹; M. Kamangar¹; S. Ashrafi^{* 2}

¹Department of Hydrology and Meteorology, Faculty of Humanities, Zanjan University, Zanjan, Iran

²Faculty of Planning and Environmental Sciences, University of Tabriz, Tabriz, Iran

Abstract

Introduction
Snow is a prevalent form of precipitation, particularly in mountainous and high latitude regions, characterized by ice crystals in various microscopic structures. It naturally accumulates in cold and elevated areas through the freezing of air and the unsuccessful melting of water into crystalline form (WMO, 2022). Snow cover plays a crucial role in determining water reserves, especially during warmer seasons. Monitoring snow cover is a specialized field within weather and climatology. Snow cover plays a key role in the balance of energy due to its high albedo. Climatologists and meteorologists, who analyze global climate changes, emphasize the significance of snow monitoring due to its impact on both daily weather patterns and long-term climate shifts (Bashir et al., 2010). Spatial studies of snow cover by using satellite data have become one of the high priority topics in geomatics research due to their applicability and high accuracy. Considering that the snow cover area in many regions of the world, including mountainous regions, affects water resources and meteorology, accurate spatial analysis and investigation of changes in the area of snow cover is very important. In this regard, use of satellite data and new tools in the spatial analysis of the snow cover area, as an efficient method in geomatics research, has received much attention (Cheng et al., 2019).
Data and Method
This research examines the changes in snow cover in the western part of Iran from 2001 to 2021. The study area includes the provinces of Kurdistan, Kermanshah, Ilam, Hamadan, and Lorestan, covering a total area of 466,121 square kilometers. The region is located between latitudes 31°51'36" to 36°49'45" N and longitudes 45°27'18" to 50°04'26" E. It encompasses the northern part of the Zagros Mountain range, which serves as the entry point for western weather systems into the country. Snow cover was assessed using Modis satellite images, with the NDSI index used to identify snow. The analysis revealed a trend in snow cover, which was further examined using the Mann-Kendall method. The spatial distribution and changes in spatial components (length, width, and height) were assessed using the G* Index.
 
 
 
Results and Discussion
 
To analyze snow cover in the western region, the snow cover index was calculated by averaging the images for each period. The area of snow cover was then determined for each period. Analysis of the winter snow cover area revealed a decreasing trend. The application of the Mann-Kendall method confirmed this decreasing trend, which is statistically significant at the 95% confidence level. Additionally, considering the annual sinusoidal behavior of snow, it can be concluded that the seasonal component is the dominant factor in the region, with temperature changes primarily driven by seasonal variation due to its relative distance from the equator. Spatial analysis indicated that the distribution of snow cover follows a northwest-southeast direction, as evidenced by the standard deviation ellipse. More than 99% of snowfall is concentrated in high-altitude areas with a specific spatial arrangement. The hotspot map shows that surface snow cover is clustered in the west and southeast directions, predominantly at altitudes above 2200 meters. The clustering pattern of snow cover is more pronounced at higher latitudes and towards the western borders. These findings have important implications for water resource management, drought prediction, and the development of strategies to mitigate droughts.
 Conclusion
 This research demonstrates a decreasing trend in the area of snow cover during the winter season in the western part of Iran. Spatial analysis reveals that the major axis of snow distribution follows a northwest-southeast orientation, aligned with the mountainous terrain in that direction. The hotspot map highlights that surface snow cover is concentrated in the west and southeast directions, particularly at altitudes above 2200 meters. Hotspot analysis indicates that snow cover is clustered towards higher latitudes and more pronounced towards the western borders.

Keywords

Kendall trend; Moran; MODIS sensor; Snow cover

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