Aim: The aim of this study is to investigate the trend of snow cover changes as a climatic factor in the Alborz Mountain Range during the period 2001 to 2023 and analyze the role of spatial and temporal components in these changes.
Materials and Methods: To conduct this study, daily data from the MODIS sensor were used. The Normalized Difference Snow Index (NDSI) was calculated to extract and zone snow-covered areas. The trend change was analyzed using the nonparametric Mann-Kendall test and the Sen’s Slope method. The relationship between the NDSI index and snow cover area was also evaluated through linear regression.
Findings: The results revealed that snow cover in the Alborz Mountains exhibited a decreasing trend during most seasons between 2001 and 2023, particularly in winter and spring. This decline was statistically significant in terms of both mean and minimum snow cover extent during winter, while in summer and autumn, the trend was more variable. Furthermore, comparison of snow cover trends with seasonal temperature and precipitation patterns indicated that increased winter temperatures and reduced precipitation—especially at lower elevations—had a noticeable impact on the reduction in snow persistence and spatial extent. These patterns were also reflected in the time series analyses and elevation profiles.
Conclusion: Spatial distribution of snow cover was directly related to elevation and geographic location, with the highest NDSI values observed in the western and central highlands. Although climatic variables were not directly analyzed in this study, the concurrent decline in snow cover with documented increases in seasonal temperatures reported in previous research suggests potential indirect impacts of climate conditions on snow dynamics in the region.
Innovation, application of results: The use of daily and long-term MODIS data, along with accurate statistical methods for analyzing trends and transition points, is considered an innovation of this study.