1998-2017年祁连山南坡不同海拔、坡度和坡向生长季NDVI变化及其与气象因子的关系

Changes of growing season NDVI at different elevations,slopes,slope aspects and its relationship with meteorological factors in the southern slope of the Qilian Mountains,China from 1998 to 2017

祁连山是我国西北地区重要的水源涵养保护区,是我国地形第一、二阶梯分界线,对气候变化极其敏感。基于气温、降水量和归一化植被指数(NDVI)数据,使用趋势分析、小波分析和相关分析方法,结合数字高程模型(DEM)数据,从海拔、坡度和坡向的角度探讨祁连山南坡NDVI变化及其与气温和降水的关系。结果表明:1998-2017年,祁连山南坡生长季NDVI整体呈增长趋势,增长趋势为0.023·10 a^-1。NDVI值在不同海拔、坡度和坡向上的变化存在差异性,NDVI值随海拔的升高呈先增后降趋势,海拔2700~3700 m区域的植被覆盖状况较好,>4700 m区域的植被出现退化现象;NDVI值随坡度增加呈降低态势;NDVI值在坡向上的差异较小,但阳坡的植被覆盖状况好于阴坡。生长季NDVI与气温、降水的关系密切,生长季NDVI、气温、降水均具有14年的变化周期,而不同海拔、坡度、坡向的植被受到气温和降水的影响不同,海拔<3700 m、>4700 m区域、坡度<25°区域和各坡向区域的植被均易受降水影响。

Qilian Mountains is an important water conservation area in Northwest China,which is the boundary between the first and second steps of China’s topography and is sensitive to climate change.Based on the data of temperature,precipitation,normal difference vegetation index(NDVI),and digital elevation model(DEM)data,we analyzed NDVI change and its relationship with temperature and precipitation along the elevation,slope and slope aspect in the southern slope of Qilian Mountains using tendency analysis method,wavelet analysis and correlation analysis.The results showed that,from 1998 to 2017,NDVI value of the growing season presented increasing trend by a rate of 0.023·10 a^-1.Changes of NDVI differed at different elevations,slopes and slope aspects.NDVI increased first and then decreased with elevation.The vegetation coverage at 2700-3700 m was good,and degraded in the area of>4700 m.NDVI reduced with the increases of slope,which showed little difference in different slope aspects but was better in sunny slope than in shade slope.NDVI of the growing season was closely related with temperature and precipitation.NDVI,temperature and precipitation in growing season all had a 14-year cycle.Vegetation at different elevations,slopes and slope aspects was differently affected by temperature and precipitation.Vegetation in areas with altitude<3700 m,>4700 m,slope<25°and each slope direction was more sensitive to precipitation.