城市化背景下植被物候动态变化及驱动因素

Dynamic changes and driving factors of land surface phenology under the background of urbanization

快速城市化会对植被物候带来显著影响,但当前影响城市植被物候时空变化的因素仍不清楚。本研究以京津冀城市群为研究区,采用5种拟合方法构建归一化植被指数曲线,通过阈值法获取京津冀城市群2001—2019年的城市植被物候特征,比较城市建成区与山区的春季和秋季物候,在此基础上分析降水、气温以及城市地表温度对植被物候的影响。结果表明:2001—2019年,京津冀城市群城市建成区植被生长季开始日期(SOS)平均比山区早16.88 d,城市建成区植被生长季结束日期(EOS)比山区晚12.22 d。研究期间,京津冀城市建成区植被SOS逐步延迟,而山区SOS逐步提前,并且城市建成区物候的变化率比山区快,因此,二者SOS的差值随时间变化而显著减小(-0.58 d·a^(-1));秋季物候方面,城市建成区和山区EOS都表现为延迟趋势,但二者差值随时间变化并不显著(-0.10 d·a^(-1))。城市建成区地表温度对SOS的贡献与气温较为接近;而山区地表温度对SOS的贡献仅为气温的1/2,说明城市内部的热岛效应和气温共同影响城市植被物候的变化,并且二者贡献几乎相等。本研究结果有助于理解城市化对植被物候动态变化的作用,可为进一步评估城市植被碳汇潜力提供参考。

Rapid urbanization would have significant impacts on vegetation phenology.However,the factors influencing the spatiotemporal changes in urban vegetation phenology are still unclear.We used five fitting methods to construct normalized difference vegetation index(NDVI)curves in the Beijing-Tianjin-Hebei urban agglomeration,and obtained the phenology characteristics of urban vegetation in this area from 2001 to 2019 by the threshold method.We compared the spring and autumn phenology in urban built-up areas and hilly areas,and analyzed the effects of precipitation,air temperature,and land surface temperature(LST)on vegetation phenology.The results showed that from 2001 to 2019,the start of the growing season(SOS)in urban built-up areas in the Beijing-Tianjin-Hebei agglomeration was on average 16.88 days earlier than that in hilly areas,and that the end of the growing season(EOS)in urban built-up areas was 12.22 days later than that in hilly areas.During the study period,the SOS of vegetation in urban built-up areas of the Beijing-Tianjin-Hebei region had been gradually delayed,while that in hilly areas was gradually advanced,and the rate of change of phenology in the urban built-up areas was faster than that in the hilly areas.The difference between the SOS of the two areas decreased significantly over time(-0.58 d·a^(-1)).As for the EOS,the urban built-up areas and hilly areas both showed a trend of delayed,but the differences between them was not significant with time(-0.10 d·a^(-1)).The contribution of LST in the urban built-up areas to SOS was close to that of air temperature,while the contribution of LST in hilly areas to SOS was only 1/2 of that of air temperature,indicating that the heat island effect and air temperature within the city jointly influenced urban vegetation phenology,and their contributions were almost equal.The results could help understand the role of urbanization in the variations of vegetation phenology and provide a reference for further assessment of carbon sink potential of urban vegetation.