نوع مقاله : مقالات پژوهشی
نویسندگان
1 دانشگاه زنجان
2 دانشکده جغرافیا و برنامه ریزی دانشگاه تبریز
چکیده
کلیدواژهها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
Introduction
Snow is one of the precipitations form especially in mountainous and high latitude areas, which can be seen as ice crystals in different microscopic forms. Snow cover is formed naturally in cold and mountainous regions due to freezing of air and failed melting of water in crystalline form (WMO, 2022) and it is one of the most important influencing factors in the amount of water reserves, especially in the warm seasons of the year. Snow cover monitoring is one of the special topics in weather and climatology. Snow cover plays a key role in the balance of energy due to its high albedo. According to climatologists and meteorologists who study climate changes in a global perspective, because the physical properties of snow affect daily and even long-term climate changes, snow monitoring is a necessity (Bashir et al., 2010). Spatial studies of snow cover by using satellite data have become one of the most important 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
In this research, the changes of snow cover during the period of 2001-2021 in western part of Iran have been studied. The studied area includes the provinces of Kurdistan, Kermanshah, Ilam, Hamadan and Lorestan. This region with 466.121 square kilometers located between the latitudes of 31ᵒ51'36" to 36ᵒ49'45" N and 45ᵒ27'18" to 50ᵒ04'26" E. Northern part of the Zagros Mountain range located in this region and this region is the place of incoming western systems to the country. To checking snow cover, Modis satellite images and for snow identify NDSI index have been used. The investigations have shown that there is a trend in the snow cover of the region. For this reason, Man – Kendall method used to reveal the trend. For study spatial distribution of data and changes in spatial distribution in terms of spatial components (length, width and height), G* Index was used.
Results and Discussion
For studying snow cover in the west of the country, at first, the snow cover index of the region was extracted as the average of the images for each separate period. Then, the area of snow cover areas was obtained for each period. Examining the area of snow cover for the middle of winter shows a decreasing trend in the data. Therefore, the Man-Kendall method was used for a more detailed investigation of the snow cover trend. Applying this method also confirmed the decreasing trend in the snow cover in the west of the country. This decreasing trend is significant at the 95% confidence level. Furthermore, considering the annual sinusoidal behavior of snow, it can be concluded that the seasonal component dominates the entire region, and the changes in temperature in this region are due to the seasonal variation, given its relative distance from the equator. Spatial analysis results indicate that snow cover distribution follows the northwest-southeast direction of the standard deviation ellipse, where more than 99% of snowfall is concentrated in the high-altitude areas with a specific spatial arrangement. The hot spot map shows that the surface snow cover of the soil is clustered in the west and southeast directions, and at higher altitudes above 2200 meters. The clustering pattern of snow cover is more towards the high latitudes and towards the western borders. The results of this study can be useful in managing water resources, predicting and planning for droughts, and developing strategies to combat them.
Conclusion
The results of this research show a decreasing trend in the area of snow cover in the winter season. The results of the spatial analysis showed that the direction of the oval is three times the spatial standard deviation from northwest to southeast, more than 99% of the snow distribution, depending on the spatial arrangement of the heights, precipitation is spread in this direction. The map of hot spots showed that the surface snow is clustered in the direction of west and southeast and at altitudes higher than 2200 meters. The analysis of hot spots showed that the snow cover is clustered towards high latitudes and more towards the western borders.
کلیدواژهها [English]
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