Trend Analysis of Snow- covered Days in Iran based on Remote Sensing Data

Snow-covered areas and its variations are important parameters in hydrological and climatic systems. For the regions that snowmelts supply needed water, snow cover trend analysis is of great importance. Many big rivers of Iran originate from snow glaciers in mountains. So, investigation of snow cover changes is actually important. In the present study, the changes of snow-covered days in different elevation zones in Iran have been calculated via using MODIS Terra and MODIS Aqua data. The highest resolution data of these products that are available at 500m resolution were applied from 1382 to 1393. The Digital Elevation Model (Dem) of Iran that is in accordance to snow data both in resolution and projection system was exploited from NASA web site. In the first step, the frequency of snow covered days was calculated for each of the elevation zones from 1500 to 5500 in the intervals of 100 m and, as the second step, the trend of each zone was analyzed using Mann-Kendall test. The results indicated that in the months of Farvardin, Tir, Amordad, Shahrivar, Azar, Bahman, and Esfand no significant trend exists in any of the elevation zones. However in the months of Ordibehest and Khorad, there were negative trend in twenty one and ten elevation zones, respectively. It was also noticed that some positive trend exist in some of the individual elevation zones in the months of Mehr, Aban and Dey. In these aforementioned months, the numbers of elevation zones with positive trend were 2, 1 and 1 respectively.