长三角地区夏季地表热环境的季节内和日夜变化特征

Intra-seasonal and diurnal variations of summer surface thermal environment in the Yangtze River Delta

基于中分辨率成像光谱仪(MODIS)遥感反演的地表温度数据、土地利用数据以及植被覆盖数据,对长三角城市群及周边地区2013~2017年夏季地表热环境的时空分布特征及其驱动因子进行了研究.结果表明:①夏季地表高温风险区(即高温区和亚高温区)在日间主要分布在皖北农田覆盖地区、长三角城市群的城市建筑覆盖地区以及浙南的少数城市建筑和农田用地;夜间地表高温风险区转换为长江流域沿线的水体覆盖区域和城市群建成密集区.②季节内变化表现为从6月份到8月份地表高温风险区在空间上逐渐从长三角的皖北和苏北区域向长三角城市群片区转移;长三角北部区域地表高温风险区比例逐渐减小,而长三角城市群片区地表高温风险区比例逐渐增加.③地表热环境的空间分布与下垫面覆盖类型的空间分布有很好的对应关系,城建用地区域的高温风险比例要显著高于其他下垫面覆盖类型区域;皖北地区的夏季农作物轮作改变了地表的植被覆盖度,导致该地区的季节内和日夜变化特征不同于其他地区;地表高温风险季节内变化规律则表明植被覆盖度的提高对于减少高温风险区比例具有显著作用.

Based on MODIS-based land surface temperature(LST)data,land use and land cover change(LUCC)data and normalized difference vegetation index(NDVI)data,the temporal and spatial characteristics and the associated driving factors of summer surface thermal environment in the Yangtze River Delta(YRD)megalopolis from 2013 to 2017 were investigated.The results show that:①The summer surface-high-temperature risk zones(i.e.,high LST zone and sub-high LST zone)were mainly distributed in the day time on the farmland covering areas in the north of Anhui,urban architectural covering areas of the YRD and some urban buildings and some farmland in southern Zhejiang,while the surface-high-temperature risk zones transferred to the water-covered areas and urban densely populated areas along the Yangtze River at night.②The intra-seasonal variations show that from June to August,the surface-high-temperature risk zones gradually shifted from the north of Anhui and the north of Jiangsu to the YRD megalopolis.The study area presents two opposite trends of intra-seasonal variations:the surface-high-temperature risk zones in the northern part of the YRD are gradually mitigating,while the surface-high-temperature risk zones in the YRD Delta megalopolis are gradually increasing.③The spatial distribution of the surface thermal environment is highly related to the spatial distribution of the underlying surface coverage type,and the surface-high-temperature risk zones of urban construction land areas are significantly higher than other underlying surface coverage types.Summer crop rotations in the northern part of YRD have changed the vegetation coverage of the surface,resulting in the difference between intra-seasonal and diurnal variations in this area from those in other areas.The seasonal variation of surface-high-temperature risk zones indicates that improvement of vegetation coverage has a significant effect on reducing surface-high-temperature risk zones.