海河上游典型流域植被动态演变规律及其对气候因子的响应

Variation Regime of Vegetation Dynamics in the Upper Reaches of Hai River and Its Response to Climatic Factors

植被动态是地球生物化学循环和陆地水循环的关键过程,也是环境变化的重要指示因子。以海河上游典型流域蔡家庄流域为研究区域,采用2000—2016年的MODIS NDVI数据作为植被数据,研究了该区域植被年内和年际动态变化特性及其与关键气候要素的相关关系及响应规律。研究结果表明,NDVI年内变化过程呈现明显的“单峰”特征,最小值发生在冬季和早春,于7月下旬达到峰值;年际变化表现出明显的趋势性,其中年平均NDVI、年最大NDVI均呈显著增加趋势,起始生长日期趋于提前,生长期长度亦明显延长。年际尺度上,NDVI对降水变化呈正向线性响应,且二者相关性较好,而与气温的相关性较弱;年内尺度上,NDVI对降水和气温的相关性均较好,都呈现出非线性正向响应,即降水和气温都存在某个阈值,使得NDVI的响应规律在阈值两侧呈现明显差异。

The vegetation dynamics is the significant process of the earth′s biochemical cycle and the terrestrial water cycle,and also an important indicator of environmental change.This paper takes Caijiazhuang watershed,a typical watershed in the upper reaches of Hai River,as the research area,and the MODIS NDVI data from 2000 to 2016 is used as vegetation data to study the characteristics of annual and inter-annual dynamic change of vegetation in this area,as well as its correlation with key climate factors and response rules.The research results show that the annual change process of NDVI presents a clear“single peak”characteristic,with the minimum value occurring in winter and early spring and reaching a peak in late July.The inter-annual change shows a clear trend,in which the annual average NDVI and the annual maximum NDVI both increase significantly.The initial growth date tends to advance,and the length of the growing period is also significantly prolonged.On the inter-annual scale,NDVI responds to the linear change of precipitation positively,and the correlation between the two is sound,but the correlation with the temperature is not strong.On the intra-annual scale,the correlation of NDVI to the precipitation and the air temperature is sound,and the non-linear positive response is presented,that is,the precipitation and the air temperature have a certain threshold value,so that the response rule of the NDVI is obviously different at the two sides of the threshold value.