2001-2012年青藏高原积雪覆盖率变化及地形影响

Study on Variation of Snow Cover and Its Orographic Impact over Qinghai-Xizang Plateau during 2001-2012

基于2001一2012年MODIS获取的青藏高原积雪面积比例(SCF)数据,利用统计方法分析了SCF时空分布特征及其变化趋势。结果表明,从10月至次年4月是青藏高原持续性积雪较多的月份,其中2月持续性积雪面积最大,达到92.93×10~4km^2。5月之后积雪面积开始递减,7月最低(仅12.37×10~4km^2);从9月起开始急剧增加,10月达到一个相对稳定的水平。2001—2012年间逐年平均持续性积雪面积在55×10~4~80×10~4km^2之间,并呈3年左右的周期振荡。高的山脉对应大的积雪面积比例,但高原内部积雪面积比例却较小。在5 km以下的地区基本上是冬季高、夏季低的趋势,5 km以上的地区平均积雪面积比例由于受常年积雪和降雪反馈的作用有双峰型的月变化特征。不同坡向的积雪面积比例也呈现较大差异:北向山坡最大,西向、东向次之,南向的最小,引起这个变化的主要原因是不同坡向条件下的太阳辐射差异导致的。10月至次年4月的平均积雪面积比例随坡度增加而急剧增加,在5—9月平均积雪面积比例随坡度变化较小。

The snow cover fraction（SCF） data during the period 2001 through 2012 from MODIS aboard Terra of NASA are used to derive the spatio-temporal distribution of snow,and to calculate its variation trend over the Qinghai-Xizang Plateau（QXP） using statistic analysis methods.The SCF during the months from October through the following April dominates compared with other months.Persistent snow area reaches the maximum of 92.93 × 10^4 km^2 in February.It begins to decrease gradually as of May,hits to the bottom line of 12.37 × 10^4km^2 in July.Beginning in September,SCF goes up sharply,leveling off in October.Overall,the annual mean snow area over the QXP oscillates between 55 × 10^4 ~ 80 × 10^4 km^2,showing a three-year variation cycle.Also,altitude is found to be able to exert significant influence on SCF.The higher the altitude is,the higher the SCF is over most parts of the QXP except over southwest QXP.For regions below 5 km,there is a monotonic seasonal variation trend,i.e.,higher winter SCF and lower summer SCF.In contrast,for regions above 5 km,there is a bi-modal variation trend.Aspect derived from digital elevation model can exert great influence on SCF as well.Northerly aspect corresponds to the maximum SCF,followed by westerly and easterly,and then southerly aspects.This is likely due to the solar radiation difference caused by various aspects.Similarly,SCF increases rapidly with slope during October to the following April,and then almost stays invariant during May through September.