Investigating the Role of Hydrogeomorphologic Factors and Climatic Changes in Snow Cover in the Alvand

Abstract
Introduction
Global warming has profoundly changed the climatic regions of the earth and the time and the place of snowfall, which has caused a lot of damage to humans, especially in recent decades. Indeed, depending on the nature of the climatic regions, these changes are diverse and varied. Mountains and valleys play different roles in the uneven distribution of the temperature and snow. The effects of different directions can be very important in snow coverage on the northern and southern slopes. In this research, using statistical models and satellite images in the Alvand, the role of the elevation, the direction of the slope, and the effect of temperature changes on snow cover in the recent decade (2015-2006) have been investigated.
Materials & Methods
In this research, based on Landsat satellite 5, 7, and 8 imagery, the data from the visible and infrared bands were used to extract snow data based on the NDSI index. The NDSI index was applied using  relationship (1) to produce snow maps on images. Indeed, the use of relative indices such as NDSI reduces the effect of the topography on the result.
(1)         
To investigate the role of the Alvand in snowfall in both of its northern and southern slopes and the snowfall regime changes in its windward slope and windsurf, the harmonic analysis was used. For this purpose, to analyze the snowfall co-ordinates and periodic behaviors and time variations, the monthly mean snowfall per cm with harmonic analysis was used. This analysis is given as a substring using a time series.





(2)
 

 




ResultsandDiscussion
According to the findings of the NDSI index, Tuyserkan area receives less snow (62%) than Hamadan (69%). The moist air mass ascending the western slopes of the Alvand's heights causes more rainfall than its eastern slopes. However, the temperature of Hamadan station is lower than that of Tuyserkan due to its northern slopes in the Alvand and the less energy it receives from the sun, which has made the snowfall on the northern slopes be more visible than it is on the southern slopes. The minimum and maximum temperatures have increased in the winter. This steep trend of increase in the winter temperatures along with lower snowfall indicates the effects of climate change and global warming on Hamadan and Tuyserkan regions. The value of the variance in the second harmonic reflects the effect of elevations on the region's climate. The value of the second harmonic variance in the northern slope which is 28% and significant shows the impact of topography on snowfall in the area. Indeed, the snowfall up to 28 % is related to the height and topography of the northern slopes of the Alvand.
While at Tuyserkan Station, this amount is reduced to 20%, meaning that the northern altitude of the Alvand is more effective in the snowfall.
Conclusion
The Alvand is a branch of the Zagros mountain range that passes through Hamedan province and has high peaks. The climatic phenomena of this mountain range are abundantly observed in the province. Severe winds and snowfall of the Alvand altitudes are among these phenomena. The mountainous cities of the province, including Hamadan and Tuyserkan, are among the most affected by the Alvand. This study by examining the hidden features of the climatic data by harmonic analysis and satellite images showed that the northern slope shared more than the southern slope in snowfall which was a significant amount in the second harmonic and a relative decrease in the temperature and snowfall. The northern slope was colder in the northern hemisphere and the sunrise of southern slope got more heat than those that were not exposed to the direct sunlight. The percentage of snow in the NDSI index on both sides of the Alvand confirmed this geographic reality. In general, the results showed a hidden feature of the rise in temperature and snow loss in the data and satellite imagery also recognized this fact. Considering the fact that the Alvand is a climatic region of the country's cold and mountainous regions and the sustainability of the natural environment depends on the relative stability of the climate, in order to achieve sustainable development and land use in the region, it seems that regional climate change should be considered in the context of climate change and the reduction of snowfall in the long time.