雅砻江流域生长季植被时空变化特征及对气象因子的响应分析

在全球气候变化背景下,开展植被变化对气象因子的响应研究对流域生态环境保护和水土资源合理利用具有重要的现实意义。以雅砻江流域为研究区,基于1982—2015年GIMMS NDVI数据,首先采用多种数理统计方法揭示生长季NDVI的时空变化特征,基于滞后相关系数法分析NDVI对气象因子的时滞效应,在此基础上建立各像元NDVI与气象因子的主成分回归方程,分析影响NDVI变化的主要气象因子及其贡献率,进而揭示NDVI对各气象因子的响应变化特征。结果表明:雅砻江流域NDVI在年内呈单峰型变化,峰值出现在8月,生长季NDVI年际变化呈不显著下降趋势。流域NDVI自下游向上游逐渐减小,植被退化面积占30%,改善面积占24.28%,中游植被改善和退化面积占比最大,就各植被类型变化而言,针叶林改善比重相对较大,灌丛和草甸退化较为严重。导致流域植被变化的主控气象因子为降水和气温,其对植被变化的贡献率分别为27.68%和26.31%,其中,流域上游及中游北部地区植被变化主要受气象因素影响,中游南部及下游地区植被受气象因子与其他因子(如人类活动)的共同影响。各像元NDVI变化的主控气象因子存在显著差异,降水、平均气温和相对湿度是中上游植被变化的主控气象因子,而降水和日照时数是下游植被变化的主控气象因子。流域植被对各气象因子的响应存在一定的时滞效应,植被对各气象因子滞后响应面积大小顺序为:平均风速>降水>日照时数>平均气温>相对湿度。中上游植被对主控气象因子降水、平均气温和相对湿度的响应主要为当月及滞后1个月;下游植被对主控气象因子降水的响应主要为滞后1个月和滞后3个月,而对主控气象因子日照时数的响应主要为当月。

Analysis of Vegetation Spatiotemporal Variation Characteristics and Response to Meteorological Factors in the Growing Season in Yalong River Basin

In the context of global climate change,conducting research on the response of vegetation changes to meteorological factors is important and practical for the protection of the watershed ecological environment and the rational use of water and soil resources.Based on the GIMMS NDVI data from 1982 to 2015,this paper selects Yalong River Basin as the research area.First,a variety of mathematical statistics are used to reveal the spatiotemporal characteristics of NDVI in the growing season,and the time lag effect of NDVI on meteorological factors is analyzed based on the lag correlation coefficient method.On this basis,the principal component regression equation of each pixel’s NDVI and meteorological factors is established,and the main meteorological factors that affect the changes of NDVI and their contributions are analyzed,and then the characteristics of NDVI’s response to various meteorological factors are revealed.The results showed that:NDVI in Yalong River Basin showed a unimodal change during the year.The peak appeared in August.The interannual change of NDVI in the growing season showed an insignificant decreasing trend.NDVI of the watershed gradually decreased from downstream to upstream.The vegetation degradation area accounted for 30%,and the improvement area accounted for 24.28%.The middle reaches of the vegetation improvement and degradation area accounted for the largest proportion.In terms of changes in vegetation types,the improvement of coniferous forests accounted for a relatively large proportion.The degradation of shrubs and meadows is more serious.The controlling meteorological factors that led to the change of the watershed vegetation were precipitation and temperature,and their contributions to the vegetation change were 27.68%and 26.31%,respectively.The vegetation change in the upper reaches and north midstream was mainly affected by meteorological factors,and the vegetation change in the south midstream and lower reaches was jointly affected by meteorological factors and other factors(such as human activities).There were significant differences in the main control meteorological factors of NDVI changes in each pixel.Precipitation,average temperature and relative humidity were the controlling meteorological factors of vegetation changes in the upper and middle reaches,while precipitation and sunshine hours were the controlling meteorological factors of downstream vegetation changes.The response of the vegetation in the watershed to various meteorological factors had a certain time lag effect,and the ranking of the corresponding area for different factors was:average wind speed>precipitation>sunshine hours>average temperature>relative humidity.The response of the vegetation in the middle and upper reaches to the precipitation,average temperature and relative humidity was mainly in the current month and one month later;the response of the vegetation in the lower reaches to controlling meteorological factors was mainly one month and three months later.The response to the sunshine hours was mainly in the current month.