基于多源数据的西藏地区积雪变化趋势分析

Variation of Snow Cover over Tibet Autonomous Region Based on Multi-Source Data

利用1980—2009年气象台站的观测数据、北半球NOAA周积雪产品和2001—2010年500m分辨率的EOS/MODIS积雪产品等多源资料,从不同角度对近30a来西藏区域积雪变化趋势进行了分析.结果表明:不同资料分析均显示,近30a来西藏地区积雪不断减少,尤其以近些年较为明显.近30a积雪日数、最大积雪深度总体上呈现下降趋势,尤其是进入21世纪以来,下降趋势非常明显.从秋冬春季节的积雪变化趋势来看,冬、春两季的积雪在减少,而秋季在增多,这些变化趋势都与各季节的气温和降水密切相关.NOAA资料显示,近30a来西藏地区的积雪覆盖面积正在逐步减少;季节变化略有不同,春、秋两季略呈上升趋势,冬、夏两季在减少,且夏季减少趋势较明显.MODIS资料分析表明,近10a来西藏地区的积雪总体呈下降趋势,尤其是2007年下半年开始下降明显.秋季的积雪在增加,冬、春、夏三季的积雪趋于减少,且春季的下降趋势最明显,其次为冬季,夏季的减少幅度最小.不同海拔的积雪都有减少趋势,最明显的是海拔4 000～5 000m的积雪,其次是海拔5 000～6 000m段.按地理区域分析,近10a来西藏东、西、中3个区域的积雪都呈减少趋势,其中西部的下降趋势最明显,其次为中部,东部相对较稳定.

A study is presented of variation of sow cover over Tibet Autonomous Region based on multi-resource data during 1980—2009.There are three different data are used in this paper.They are observed snow data of 34 weather stations in Tibet Region,the Northern Hemisphere monthly snow data of NOAA and MODIS eight-day snow cover productions.The results show that： 1） annual snow cover days and maximum snow depth in the region showed a decreasing trend during the 30 years.Especially since the beginning of this century,the decreasing trend has been very obvious.Seasonal snow cover days and the maximum snow depth were increasing in the autumn and decreasing in the other seasons.2） NOAA data shows that： From 1980 to 2009,snow cover area in the region had decreased gradually,with different seasonal changing trends,slightly increasing in spring and fall,but slightly decreasing in winter and summer.3） MODIS data shows that snow cover area in the region had been decreasing generally in the last 10 years,especially,since 2007.Snow cover area increased in autumn and decreases in winter and spring.The decreasing trend in spring was obvious than that in winter.According to the analysis on different elevation ranges,the snow cover area in all elevation ranges decreased generally,especially in the range of 4 000-5 000 m.Spatially,the snow cover area also had decreased for different parts of the region during the last 10 years,especially in the west part.The results which get from NOAA and MODIS are slightly different each other,since the spatial resolution,the length of time and the study area are different for NOAA data and MODIS data in this paper.NOAA data have the advantage in time length,but MODIS data is much better than NOAA data in resolution.Thus combining NOAA data with MODIS data to analyze will have more accurate result.