بررسي اثرگذاري گرمايش فراگير بر تغييرات زماني و مكاني پوشش برف و ماندگاري آن در گستره‌ي دامنه شمالي البرز مركزي

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

گرﻣﺎﯾﺶ ﺟﻬﺎﻧﯽ ﻣﯽ ﺗﻮاﻧﺪ ﺑﺮ ﺣﻮﺿﻪ ﻫﺎي آﺑﺮﯾﺰ ﺑﺮﻓﮕﯿﺮ و ﭘﺮاﮐﻨﺶ زﻣﺎﻧﯽ و ﻣﮑﺎﻧﯽ ﺑﺮف، و در ﻧﺘﯿﺠﻪ ﻧﯿﺎزﻫﺎي آﺑﯽ ﭘﺎﯾﯿﻦ دﺳﺖِ ﺣﻮﺿﻪ اﺛﺮﮔﺬار ﺑﺎﺷﺪ. ازاﯾﻦ رو، ﻫﺪف اﯾﻦ ﭘﮋوﻫﺶ ﺑﺮرﺳﯽ ﺗﻐﯿﯿﺮات ﻣﮑﺎﻧﯽ-زﻣﺎﻧﯽ ﭘﻮﺷﺶ و ﻣﺎﻧﺪﮔﺎري ﺑﺮف در داﻣﻨﻪ ﺷﻤﺎﻟﯽ اﻟﺒﺮز ﻣﺮﮐﺰي ﻣﯽ ﺑﺎﺷﺪ. از داده ﻫﺎي ﺳﻨﺠﻨﺪ MODIS و ﻧﻤﺎﯾﻪ NDSI ﺑﺮاي ﺑﺮآورد ﭘﻬﻨﻪ ﭘﻮﺷﺶ ﺑﺮف در ﺑﺎزه ﺳﺎل ﻫﺎي 2000 ﺗﺎ 2018 اﺳﺘﻔﺎده ﺷﺪ. ﯾﺎﻓﺘﻪ ﻫﺎي اﯾﻦ ﭘﮋوﻫﺶ ﻧﺸﺎن داد ﮐﻪ روﻧﺪي ﻣﻌﻨﯽ دار و اﻓﺰاﯾﺸﯽ در دﻣﺎي ﻣﺎه ﻫﺎي ﻣﯽ و ژوﺋﻦ وﺟﻮد دارد. از ﺳﻮﯾﯽ دﯾﮕﺮ ﮔﺮﭼﻪ روﻧﺪي در ﭘﻬﻨﻪ ﭘﻮﺷﺶ ﺑﺮف دﯾﺪه ﻧﺸﺪ، وﻟﯽ ﺗﺨﻤﯿﻦ ﮔﺮ ﺷﯿﺐ ﺳﻦ ﻧﺸﺎن داد ﮐﻪ ﭘﻬﻨﻪ ﭘﻮﺷﺶ ﺑﺮف در ﻣﺎه ژاﻧﻮﯾﻪ ﻧﺰدﯾﮏ ﺑﻪ 220 ﮐﯿﻠﻮﻣﺘﺮ در ﺳﺎل اﻓﺖ ﮐﺮده اﺳﺖ، ﮐﻪ اﯾﻦ اﻓﺖ ﺑﺎ اﻓﺰاﯾﺶ ﻣﯿﺎﻧﮕﯿﻦ دﻣﺎي اﯾﻦ ﻣﺎ ﻤﺒﺴﺘﮕﯽ ﻣﻨﻔﯽ ﻣﻌﻨﯽ داري داﺷﺖ )0/77-=r(. در ﺣﺎﻟﯽ ﮐﻪ در ﻣﺎه ﻣﺎرس ﺳﺎﻻﻧﻪ ﻧﺰدﯾﮏ ﺑﻪ 60 ﮐﯿﻠﻮﻣﺘﺮ ﺑﺮ ﭘﻬﻨﻪ ﭘﻮﺷﺶ ﺑﺮف اﻓﺰوده ﺷﺪه اﺳﺖ. همبستگي ﻣﺜﺒﺖ و ﻣﻌﻨﯽ داري )0/81=r( ﺑﯿﻦ ﭘﻬﻨﻪ ﭘﻮﺷﺶ ﺑﺮف و ارﺗﻔﺎع ﺑﺮف، و ﻫﻤﺒﺴﺘﮕﯽ ﻫﺎي ﻣﻨﻔﯽ ﻣﻌﻨﯽ داري )0/80- ﺗﺎ0/60- =r( ﻣﯿﺎن ﭘﻬﻨﻪ ﺳﺎﻻﻧﻪ ﭘﻮﺷﺶ ﺑﺮف و ﻣﯿﺎﻧﮕﯿﻦ دﻣﺎي ﺳﺎﻻﻧﻪ ﻫﻮا دﯾﺪه ﺷﺪ. اﯾﻦ ﯾﺎﻓﺘﻪ ﻫﺎ ﻧﺸﺎﻧﮕﺮ اﺛﺮ ﺗﻐﯿﯿﺮات زﻣﺎﻧﯽ و ﻣﮑﺎﻧﯽ دﻣﺎ ﺑﺮ ﮔﺴﺘﺮه و ﻣﺎﻧﺪﮔﺎري ﺑﺮف ﻣﯽ ﺑﺎﺷﻨﺪ. ﺑﺎ ﮐﺎﻫﺶ ﺑﻠﻨﺪي ﺣﻮﺿﻪ از ﻏﺮب در ﻫﺮاز، ﺑﺎ ﻣﯿﺎﻧﮕﯿﻦ ارﺗﻔﺎﻋﯽ 2059 ﻣﺘﺮ، ﺑﻪ ﺳﻮي ﺷﺮق در ﺣﻮﺿﻪ ﺗﺠﻦ، ﺑﺎ ﻣﯿﺎﻧﮕﯿﻦ ارﺗﻔﺎﻋﯽ 980/7 ﻣﺘﺮ، از ﭘﻬﻨﻪ ﭘﻮﺷﺶ ﺑﺮف و ﻣﺎﻧﺪﮔﺎري آن ﮐﺎﺳﺘﻪ ﻣﯽ ﺷﻮد. از ﯾﺎﻓﺘﻪ ﻫﺎي اﯾﻦ ﭘﮋوﻫﺶ ﻧﺘﯿﺠﻪ ﮔﯿﺮي ﻣﯽ ﺷﻮد ﮐﻪ ﺗﻐﯿﯿﺮات دﻣﺎ در اﯾﻦ ﮔﺴﺘﺮه ﻫﻢ روند گرﻣﺎﯾﺶ ﻓﺮاﮔﯿﺮ اﺳﺖ، در ﺣﺎﻟﯽ ﮐﻪ اﯾﻦ ﮔﺮﻣﺎﯾﺶ ﺑﺮ ﭘﺮاش )وارﯾﺎﻧﺲ( ﭘﻬﻨﻪ ﭘﻮﺷﺶ ﺑﺮف اﺛﺮ ﮔﺬاﺷﺘﻪ اﺳﺖ.

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.