长江源区典型流域积雪年变化及其与气温、降水的关系

对长江源区冬克玛底河流域2005年1月—2006年9月积雪空间分布特征、雪盖变化进行了分析,探讨了2005年暖季(5~9月)积雪覆盖与同期气温和降水量之间的关系.结果表明:积雪主要分布在河谷两侧的山坡、山顶、冰川前沿和冰川上,宽广平坦的河谷积雪很少;在暖季,流域降水多、气温较高,积雪主要分布在冰川区.作为一种特殊的下垫面,沼泽化草甸和冻土丘对积雪分布也有较大的影响.从两年的积雪覆盖率变化来看,在降雪少而气温低的1~4月积雪覆盖率变化剧烈;5月份降雪增多,但由于气温也在逐步回升,使得积雪覆盖率还是变化剧烈;10~11月降雪较多而且气温较低使得积雪覆盖率保持在80%以上的覆盖水平;6~8月因气温和地温较高,尽管降水多以固态形式降落,但在地面保留的时间极短,故积雪覆盖面积较小.在暖季(5~9月)降水对积雪覆盖的影响微弱,而温度是流域积雪覆盖变化的主要影响因素.

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.