Statistical Analysis of Time Series of Snow-Covered Area Obtained from Satellite Images in Mazandaran Province

 The snow variable plays an important role in hydrological cycles and is an essential component of the climate system. Is one of the basic applications in the field of water resources management, especially in areas where snowfall has a large share of precipitation. Therefore, the main purpose of this study is to investigate the trend of these changes in the watershed of the northern slope of the Alborz Mountain range in Mazandaran province in abnormal climatic conditions in the last decade.

First, MODIS sensor data was received daily from NASA's National Snow and Ice Database (NSIDC) with a 500*500 m embedding capacity. The received images are related to the period 2000-2018. To process the images, pre-processing operations were first performed on them in the ENVI 5.3 software environment. The NDSI index was used to estimate the snow cover. Mann-Kendall test and age line slope estimator method were used to study the trend of snow cover changes. Pearson correlation coefficient was also used to investigate the correlation between snow cover level and climatic parameters.

 Examination of the trend of snow cover level seasonally and annually showed that snow cover in winter has decreased by about -50.41 square kilometers per year. From the elevation standpoint, snow cover is regressing, as its trend is decreasing across all elevation levels, especially at altitudes of 1600 to 2500 meters. The result of this study shows that there is a negative correlation between snow cover and net radiation and a positive correlation with soil moisture at a 95% confidence level. A comparison of the correlation between snow cover status and time and different elevation classes with temperature and precipitation shows that in most cases negative snow cover anomalies are associated with positive temperature and negative rainfall anomaly, which is significant at 95% level. While acknowledging the decline of snow stocks on the northern slope and the increasing increase in freezing temperatures, the management of downstream basin water resources should be reconsidered.

 In general, the results show that the trend of snow cover seasonally and annually has a decreasing trend. It can also be concluded that the trend of snow cover of different altitudes in the northern slopes of Central Alborz has decreased and receded. The greatest effect of temperature increase is observed in spring. This is because the energy required to melt snow is usually provided by short-wave radiation in early spring, and as the intensity of the net radiation current increases due to the increase in short-wave input radiation and the whiteness occurs due to the decrease in height and snow-covered range, the snow melting rate increases. Therefore, with increasing temperature and changing climatic conditions, winter precipitation, which will turn into snow accumulation, has decreased and can affect the runoff caused by these precipitations in spring.