Annual Variations of Snow Cover and Its Relation to Air temperature and Precipitation in Dongkemadi River Basin in the Source Regions of the Yangtze River

On the basis of 500-meter resolution MODIS10A2 snow products,in this paper,the spatial characteristics of snow cover and the change of fraction of snow coverage from January 2005 to September 2006 are analyzed,also the relations are studied between snow cover and precipitation,snow cover and air temperature from May to September in the Dongkemadi River Basin in the source regions of Yangtze River,in 2005.The results showed that the distribution of snow was at the tops and slopes of mountains,the top and front of glacier,and little of snow was distributed at the flat river valley;The right side of the river had much more snow cover than the left side;In the warmer season,because of more precipitation and high air temperature,the snow was mainly distributed at the top of glacier;As a special ground conditions,the marshy meadow or frost mound also affected the spatial distribution of snow.The fraction of snow coverage monitored for two years showed that from January to April,because of little precipitation and low air temperature,the fraction of snow coverage changed drastically.In May,precipitation gradually increased,but the increased air temperature made the fraction of snow coverage also changed drastically;the relatively more precipitation and low temperature resulted in the fraction of snow coverage being above 80% form October to November;precipitation was in a solid state but snow was melted quickly from June to August,because of relatively high air and ground temperature,so the fraction of snow coverage was relatively small.The analyses of snow cover and air temperature from May to September in 2005 show that the relation between snow cover and precipitation was not significant,but air temperature was the main factor affecting the snow cover.Precipitation state from rain to sleet and then to snow was the main reason for the non-evident relation between snow cover and precipitation from May to September.