Abstract:

Investigating the spatiotemporal variations of vegetation and land surface temperature (LST) is of great importance for urban agglomerations in the context of rapid urbanization. It is urgent to understand the ecological environment changes and facilitate the sustainable development of urban agglomerations. In this study, Moderate Resolution Imaging Spectroradiometer (MODIS) enhanced vegetation index (EVI) and LST data, including the sixteen-day MOD13A2 and eight-day MOD11A2 products, were used to systematically analyze the spatial and temporal variation trends of the EVI and LST in 11 cities within the Guangdong-Hong Kong-Macao Greater Bay Area (GBA) of China during 2001-2020. The results showed that the average EVI value in the GBA increased significantly from 2001 to 2020, with a stronger increase in summer and winter. The winter EVI value increased at a rate of 0.004 a^-1 (P<0.01), which was consistent with the annual EVI growth rate; the summer EVI value’s growth rate was greater than 0.005 a^-1 (P<0.01). The annual, summer, and winter EVI values of the 11 cities also showed significant increasing trends, the smallest increasing rate of which was 0.001 a^-1. Hong Kong and Zhuhai cities had greater EVI growth rates in the winter times compared with those in the summer times. The GBA exhibited the highest average LST (greater than 30 ℃) during the summer daytime between 2001 and 2020. Seven cities had the average summer daytime LST greater than 30 ℃. In summer, the difference ratio between the daytime and nighttime LST values in all the cities was greater than 20%. However, in winter, the temperature difference ratio between the daytime and nighttime was greater; all cities had a difference ratio over 40%. There was no significant annual increasing trend and seasonal increasing trend in the summer times in terms of the daytime and nighttime LST across the entire GBA as well as the individual cities. The daytime and nighttime LST values in the winter times during 2001 and 2010 had a similar trend. However, from 2011 to 2020, the daytime and nighttime LST of 11 cities during the winters exhibited a significant increasing trend. Guangzhou was observed with the greatest nighttime LST increasing rate at 0.376 ℃∙a^-1, while Hong Kong was found to have the lowest nighttime LST increase rate at 0.205 ℃∙a^-1. The correlation analyses indicated that the 20-year averaged daytime and nighttime LST was negatively correlated with the annual EVI values and seasonal EVI values for the summer and winter times with statistical significance. The correlation coefficient between the EVI value and the nighttime LST was greater than that between the EVI value and the daytime LST for all the cities. The outcome of this research can provide theoretical and practical support for the ecological protection and the development of urban agglomerations.

Key words: Guangdong-Hong Kong-Macao Greater Bay Area, Moderate Resolution Imaging Spectroradiometer, land surface temperature, enhanced vegetation index, temporal trend analysis, rapid urbanization

摘要：

研究快速城市化背景下的城市群植被和地表温度的时空变化特征对研究城市群的生态环境变化、促进城市群可持续发展等方面具有重要意义。利用2001—2020年MODIS提供的MOD11A2地表温度产品和MOD13A2增强植被指数（EVI）产品,系统分析近20年粤港澳大湾区城市群快速城市化过程中11个城市的植被和地表温度在不同时间尺度上的时空变化趋势。结果表明,2001—2020年粤港澳大湾区整体EVI呈显著增加趋势,冬季EVI显示了与全年EVI一致的增长速率,均为0.004 a^-1（P<0.01）;夏季EVI增长趋势最明显,其增长速率达到了0.005 a^-1（P<0.01）。所有城市年、夏季和冬季的EVI也呈现显著的增长趋势,最小的EVI增长速率为0.001 a^-1;香港和珠海的冬季EVI增长速率大于夏季EVI增长速率。2001—2020年粤港澳大湾区夏季白天平均地表温度最高,超过30 ℃;7个城市的夏季白天平均地表温度均超过30 ℃。夏季大湾区所有城市的白天与夜间地表温度的差比均大于20%,且各城市冬季白天与夜间的温度差异更大,地表温度差比均大于40%。大湾区及各城市全年、夏季以及2001—2010年冬季白天和夜间地表温度整体上无显著增温趋势（P<0.05）。2011—2020年11个城市冬季白天和夜间地表温度均呈现出极显著的升高趋势;升温最大的是广州夜间地表温度,幅度达到了0.376 ℃∙a^-1;最低的是香港白天地表温度,为0.205 ℃∙a^-1。相关性分析表明,所有城市20年平均白天和夜间地表温度与EVI在全年、夏季和冬季呈显著负相关;EVI与夜间地表温度的相关性高于EVI与白天地表温度的相关性。研究结果可为城市群生态保护与建设提供参考。

关键词: 粤港澳大湾区, MODIS, 地表温度, 增强型植被指数, 趋势分析, 快速城市化