Investigation of the effect of global warming on temporal and spatial changes of snow cover and its durability in the northern slope of Central Alborz

Global warming could affect snow-covered watersheds and the temporal and spatial distribution of snow, and thus the water needs below the basin. Therefore, the aim of this study is to investigate the spatio-temporal changes of snow cover and snow retention in the northern aspects of Central Alborz. The Normalized Difference Snow Index (NDSI) extracted from MODIS satellite images was employed to estimate snow cover during 2000 - 2018 intervals. The findings of this study showed that there is a significant and increasing trend in the temperatures of May and June. On the other hand, although there was no trend in the snow cover, the Sen's slope estimator showed that the snow cover in January decreased by about 220 km per year, which had a high negative correlation with the increase in the average temperature of this month. (r = - 0.77), while in March, the snow cover increased by nearly 60 kilometers a year. There was a significant positive correlation (r = 0.81) between snow cover and snow depth, and significant negative correlations (r = -0.80 to r = -0.60) were found between the annual snow cover and the average annual air temperature. These findings indicate that the effect of temporal and spatial changes in temperature on the extent and persistence of snow cover is meaningful. By reduction of the basin’s height from the west in Haraz, with an average height of 2059 m, to the east in the Tajan basin, with an average height of 980.7 m, the snow cover area and its durability reduced. From the findings it is concluded that temperature changes in this region follow the global warming trend, while this warming has affected on the variance of the snow cover extend.