Snow Cover Periods Analysis In The Typical Area Of The Tianshan Mountains Based On Remote Sensing

Mountain glaciers and snow cover play an important role in water budget of many regions in the world. At high-latitude mountain area, snow melt could be an important part of the total yearly runoff volume. The northern Xinjiang area is one of the most important snow cover region and the pivotal pastoral areas in China. Most of the region accumulates massive snow in winter, but less in the southern part of the area near the dessert. Therefore, snow cover periods vary wildly in the region. Monitoring snow cover periods in pastoral areas plays a significant role in taking measures against snow disasters. Detection of the annual timing of snow cover onset dates, ending dates and the snow cover periods can provide useful indicators of climatic change. Futhermore, snow cover periods are the important input parameter of modeling snowmelt runoff. Studying snow cover periods in the Tianshan Mountains is important to both scientific research and practical application.Based on MODIS snow cover products and the station observed data, this thesis investigated the differences of snow cover periods. First, this research obtained the snow cover onset dates and snow cover ending dates on MODIS snow cover products through comparing with the dates obtained by observed data. Based on the observed data, change of regions’snow cover area was used to divide the snow cover periods. Finally, the difference of snow cover periods in different regions, at different altitude, slope and aspect was analyzed. The main contents and conclusions are as follows:(1) Snow cover onset dates and ending dates were obtained based on the observed data in the stations. Compared with the periods gotten by MODIS snow cover products, the two snow cover periods reached a good agreement. Based on the observed data, the characteristics of the snow cover ceasing dates and snow cover melting dates were analyzed on the remotely sensed data and finally change of regions’snow cover area was used to divide the snow cover period into three different stages.(2) The snow cover onset dates and snow cover ending dates change significantly in different altitudinal belt. The trend of snow cover periods change is:the snow cover starts earlier and ends later with increasing altitude. The snow cover ceasing dates become earlier with increasing altitude and snow cover melting dates become later based on the temperature gradient.(3)The snow cover periods in five different regions of the study area are compared in this thesis. The snow cover onset days advance and the snow cover ending dates delay from west to east, from south to north. The snow cover ceasing" dates have no significant difference in these regions except that in the central region it is slightly earlier. The snow cover melting dates in the west are later than that in the east and ones in the north are later than that in the south.(4) The distribution of snow cover periods in the different aspect is:the snow cover starts earlier in the northwestern, western and northern aspect and the snow cover ends later compared with other aspects. The snow periods are short in the southern aspect. The snow cover ceasing dates have no big differences among those aspects, but the trend of snow cover melting dates is like that of the snow cover ending dates. From southern to northern aspect, the snow cover melts later. The inter-annual trend is similar in every aspect. The snow cover starts earlier and ends later in all aspects in the year od2007-2008and2008-2009. These two years are typical less snow years.(5) With the increase of the slope, the snow cover onset dates become earlier, and the snow cover ending dates become later. The inter-annual variation is different in the extremely high or low slope. With higher slope, snow cover ceasing dates and melting dates are hardly distinguished since the regions where the slope is larger than40are in the high mountainous area and covered by snow all the year.For future research, the cloud removal method for the MODIS snow cover products should be improved to make the study area be cloud free. When analyzing the snow cover difference, more factors can be taken into account, like the temperature field and precipitation. Futhermore, with the development of remote sensing technique, a longer sequence remotely sensed data should be analyzed.