Snow Cover Changes of Zagros Range in 2001-2016 Using Daily Data of MODIS

Snow cover (SC) is the main part of global cryosphere that covers about 46 million square kilometer of earth surface. Seasonal SC and snow storage provides the required water of around 1/6 of world population. About 98 percent of global SC is in the northern hemisphere. Southern and southwestern mountain range of Iran, called Zagros is located in the mid-latitudes that is exposed to the northern hemisphere westerlies resulting in high amount of rain and snowfall. This region contains 40 percent of Iran's water storage. Monitoring and evaluation of seasonal SC is essential for managing winter tourism, transportation, environment, land cover, water and irrigation and also essential in runoff modeling. In our study area snow gauges are insufficient and sparse, therefore monitoring spatial changes of Snow Cover Area (SCA) is difficult. MODIS images lunched on TERRA and AQUA platforms are suitable data source for estimating SC, because they provide daily images with 500 meter spatial resolution. The aim of this study is detecte and analyze SC variations and trends in Zagros mountain range using daily images of MODIS in order to determine SC variation. In this research, 348 daily products of MODIS for first days of snowy months (Months with some snow on the ground in Zagros; Dec, Jan, Feb, Mar, Apr, May, Jun) are obtained from National Snow & Ice Data Center (NSIDC) to calculate SCA. Digital Elevation Model (DEM) is used to determining snow line (SRTM 90m from Earthexplorer.usgs.gov) and total monthly precipitation of weather stations above 1500 meter elevation of the same period with SC data is used. Snow line is extracted by overlaying DEM on SCA. Then the snow line pattern is determined as the average of snow line for each day during 2001 to 2016. SCA pattern is also extracted as the average of each day during the same period. In order to calculate trends in SCA and Snow Line Man-Kendal test is used. Man-Kendal test is less sensitive too extreme values of time series. The trends of SC are investigated using Man-Kendal test results show a decreasing trend in January, May and June in 2007-2016. The highest amount of SCA decrease and snow line retrogression for January, May and June are recorded in 1250-4500 m, 2300-4500 m and 3500-4500 m altitude belts, respectively. Based on SC departure from the average, two periods are recognizable: first, from 2001 to 2008, in this period SC is above the average and is more similar to the snow cover pattern of the whole period (2001-2016). Second period from 2009 to 2016, in this period SC is more below the average and is not similar to the snow cover pattern of the whole period (2001-2016). In the second period mean SC reduction compared to the first period in Dec, Jan, Feb, Mar, Apr, May and June are 4, 67.6, 24.5, 21, 10, 47.3 and 48.4 respectively. Mean monthly precipitation changes of weather stations above 1500 meter elevation is similar to the changes of SC changes.