2001—2008年天山西部山区积雪覆盖及NDVI的时空变化特性

Spatial and Temporal Variations of Snow Cover Area and NDVI in the West of Tianshan Mountains

对于以融雪及融冰补给为主的山区河流,融雪及融冰量的多少对当地可供利用水资源量的大小起着决定作用,对河流所在的水库的正常蓄水、防洪及发电产生一定的影响.积雪时空变化规律的影响因素较多,除气温这个主要因素外,还与当地植被覆盖情况、风向、风速及太阳辐射等因素有关,因此,基于2001—2008年的MODIS积雪数据和NDVI数据分析了研究区的积雪覆盖度与NDVI时空变化特性.结果表明:天山西部山区积雪分布极不均匀,边缘山区多雪,腹地少雪,边缘山区南坡比北坡积雪多;积雪期主要集中在10月到翌年5月,积雪年际变化差异较大,积雪有减少趋势.近8a来研究区的植被有较好的改善且与降水有一定的联系,但部分区域NDVI也有减小的趋势,不同区域植被返青时间不同.通过对比分析发现,除积雪消融与NDVI有其自有的变化规律外,二者之间也有很好的相关性,但关于植被覆盖是否会对积雪的消融起加速或减缓的作用,基于此两种MODIS数据产品无法得知,有待于通过其它方法或进行野外实验确定.

Both the snowmelt and ice melting waters play an important role in regional water resources,especial for the mountainous river systems.Change in meltwater will bring some influences on the normal water storage of reservoirs,power generation,flood protection and utilizable capacity.It is also one factor that results in river occurring dam-break flood.The temporal and spatial variations of snow cover depend on many factors,such as air temperature（the main factor）and the local vegetation cover,wind direction,wind speed,solar radiation and so on.In this paper,the spatial and temporal variations of snow cover area and NDVI in the West of Tianshan Mountain is discussed based on MODIS data in 2001—2008.It is found that the snow cover distribution is also extremely uneven,more in the surrounding mountainous areas but less in the hinterland.Snow cover is more in the southern slopes than that in the northern slopes.Temporally,it is more from October to May of the next year.There is a great difference from year to year,with a decreasing tendency year by year.However,the vegetation in the study area has been greatly improving in the recent eight years,which is related to precipitation.Still NDVI in some places has also had a decreasing tendency;the turn green date is different in different regions.Comparing and analyzing shows that snowmelt and NDVI have a very good correlation,together with their own changing rule.But whether vegetation will speed up or slow down snowmelt,it is uncertain based on the two MODIS data,and further research through other methods or experiments is needed.