大气污染对京津冀地区夏季植被生长峰值的影响

Effects of air pollution on summer peak vegetation growth in the Beijing-Tianjin-Hebei region

植被物候是指示气候变化的重要因子,大气污染物变化对植被生长峰值的影响尚未得到充分探究。论文利用卫星观测的归一化植被指数(Normalized Difference Vegetation Index,NDVI)2001—2015年的时序数据,分析京津冀地区植被生长季峰值(peak of growing season,POS)、生长期最大值(_(max)imum vegetation growth,NDVI_(max))的时间变化,探究大气污染物(PM_(2.5))对POS、NDVI_(max)的影响,阐明PM_(2.5)对POS、NDVI_(max)与气象因子响应机制的影响。结果表明:燕山和太行山区POS较早且NDVI_(max)较大,东南部平原POS较晚,张家口地区、燕山和太行山区NDVI_(max)呈显著增加趋势。季前降水(季前指POS或NDVI_(max)与影响因子偏相关系数绝对值最大值对应的时间距多年平均POS的时间长度)对POS、NDVI_(max)的影响均较大,显著相关区域分别占研究区域的12.9%、15.2%;温度影响所占比例分别为8.7%、5.9%(P<0.1)。在PM_(2.5)的影响下,不同季节不同地区降水和温度的反馈不同;物候对由PM_(2.5)引起的降水和温度变化的响应同样具有空间异质性。PM_(2.5)导致中东部平原和北部燕山地区降水对POS的提前作用被低估,张家口北部丘陵地区POS的提前作用被高估,东部、南部平原和坝上地区温度对POS的提前作用被高估;整体来看,PM_(2.5)对NDVI_(max)的间接作用表现为降低NDVI_(max)(P<0.1)。长期来看,京津冀大部分地区,PM_(2.5)的直接作用表现为PM_(2.5)使POS提前、NDVI_(max)增大(P<0.1)。研究结果主要揭示了京津冀地区植被生长峰值对气候变化及大气污染物的响应,对深入理解不同地区植被生长对气候变化和大气污染变化的响应和反馈具有重要意义。

Vegetation phenology is a sensitive indicator of climate change,and the effects of different meteorological factors and changes in atmospheric pollutants on peak vegetation growth have not been fully explored.In this study,we used satellite observed normalized difference vegetation index(NDVI)data from 2001 to 2015 to investigate the temporal changes of peak of growing season(POS)and_(max)imum vegetation growth(NDVI_(max))in the Beijing-Tianjin-Hebei region by the Theil-Sen slope estimator.We also analyzed the effects of preseason temperature and precipitation on POS and NDVI_(max)considering the effects of the fine particulate matter(PM_(2.5))to investigate the indirect effect of PM_(2.5)on POS and NDVI_(max)in the region,and the direct effects of PM_(2.5)on POS and NDVI_(max)by partial correlation analyses.The results showed that earlier POS and higher NDVI_(max)occurred in the Yanshan Mountains and Taihang Mountains,POS in the eastern and southern plains were relatively late,and the NDVI_(max)in Zhangjiakou City,the Yanshan Mountains,and the Taihang Mountains showed a significant increasing trend.Preseason precipitation had a greater impact on POS and NDVI_(max)(the area where significant correlation was found accounted for 12.9%and 15.2%of the study area),which was similar to the effect of temperature(8.7%and 5.9%,respectively).Under the impact of PM_(2.5),the feedbacks of precipitation and temperature were different in different regions and seasons,and the responses of phenology to the changes of precipitation and temperature caused by PM_(2.5)also showed spatial heterogeneity.PM_(2.5)led to the underestimation of the advancing effect of precipitation on POS in the central and eastern plains and northern Yanshan Mountains,overestimation of the advancing effect of precipitation on POS in the northern Zhangjiakou area,and overestimation of the advancing effect of temperature on POS in the eastern and southern plains and the Bashang areas.Overall,the indirect effect of PM_(2.5)on NDVI_(max)was reducing NDVI_(max)(P<0.1).In the long run,PM_(2.5)would directly advance POS and increase NDVI_(max)in most areas of the Beijing-Tianjin-Hebei region(P<0.1).Our study revealed the response of peak vegetation growth to climate factors and atmospheric pollutants in the Beijing-Tianjin-Hebei region,which are of great significance for an in-depth understanding of the response and feedback of vegetation growth to changes in the climate and air pollution.