Investigating the Changes in Snow Cover in Sefidrood Drainage Basin using Remote Sensing

Snow reservoirs are one of the most important sources of water supply in Iran. This study aims to investigate the changes in snow cover in Sefidrood basin and its sub-basins. To achieve this goal, snow cover images of MODIS's MOD10cm product were used over a period of 19 years (2000 to 2019). After analyzing the images in ENVI software, the snow area of each image was calculated and, consequently, monthly values for all years of the study period were extracted and transferred to ArcGIS software. The modified Mann-Kendall test was applied to examine the annual and seasonal trends of snow cover. Then, the Sen’s slope estimator test was used to determine the rate of change. Based on the findings, it can be seen that the time of beginning and end of snow in Sefidrood basin and its sub-basins has undergone very little change. The snow cover of the basin starts in October and reaches its minimum in April after increasing towards the cold period of the year. January is the month with maximum snow cover in all sub-basins. During the period under review, the range of snow cover was maximum in the water year 2006-2007 and minimum in 2009-2010. Findings from the fit of the modified non-parametric Mann-Kendall test on the annual time series of the snow cover of the basin indicate a decrease and of course insignificant trend in most of the basin area, although sometimes slight increasing trends are also seen. In terms of spatial distribution, in the central and eastern regions of the basin, there is a significant decreasing trend of snow cover; its annual decreasing rate in some areas is 17.77% per decade. Seasonal trends are also decreasing. The highest rate of decrease is related to winter, which in some areas reaches about 33% per decade.