上海城市集群化发展显著增强局地高温热浪事件

上海作为中国城市集群化发展的典型代表,经过30余年圈层式、集群化扩张,城市建设用地面积比例高达47.9%,接近50%的生态阈值。城市群快速扩张诱发了一个以徐家汇为中心覆盖周边40 km的区域性热岛,影响高温热浪的时空分布。基于DMSP/OLS遥感夜间灯光数据构建的城市发展指数,客观地反映出1992—2013年上海西郊嘉定、青浦和东郊的浦东集群化发展特征最凸出。利用Chow检验最优分段建模法,研究发现高温热浪期间城市群热岛突变转折与区县城市发展指数超过60%的年份相对应。城市发展指数超过60%后,近郊城市继续扩张将缩小城、郊气象站的温差,诱发更大范围热岛,增强高温热浪。1977—2000年近郊区县城市发展指数低于60%,高温热浪各要素项城郊差值显著上升,而2000年西郊城市发展指数超过60%后,和市中心差值减小,快速城市化明显增强西郊高温热浪强度和持续时间。1978年以来上海西郊与远郊高温日数差值增加了1.6倍,平均气温差值增加了34.4%,平均最高气温差值增加了41.7%。高温热浪期间遥感数据显示,向西郊伸展的城市群地表温度高值区规模扩大了32.8%,是西郊高温热浪增强的驱动因子。

The exacerbated intensity and duration of the heat waves events over Shanghai as caused by urban clusters expansion

Shanghai urban clusters, the most prosperous areas in China, are experiencing the rapidly spatial growth of circle-shape expansion surrounding the urban center and clusters over suburban areas since 1981. As a result, the urban constructed area proportion about 47.9% was very close to the ecological threshold of 50% in 2013. A regional heat island covering 40 km around the Xuhui district has been induced by the rapid urban clustering expansion, and has affected the spatial distribution of heat waves. An urbanization index, represented by the remote sensing data from the Operational Linescan System instruments of the Defense Meteorological Satellite Program (DMSP/OLS), is proposed to depict the urbanization of Shanghai, which shows stronger clustering urbanization over the Jiading, Qingpu and Pudong districts. Using the Chow test method based the optimal piecewise modeling to detect the structural change in urban heat island intensities, it is found that the urban heat island intensities will occur structural change when the DMSP/OLS urbanization index exceeding 60%. Urban expansion will further induce stronger and wider regional urban heat islands effects and enhanced heat waves after the DMSP/OLS urbanization index exceeding 60%. In the period of 1977-2000, the DMSP/OLS urbanization index was lower than 60%, in which the urban heat island intensities increased significantly over all the suburban areas. However, this tendency has changed since 2001 when the DMSP/OLS urbanization index exceeded 60% in 2000 over the western suburban areas. Urban heat island intensities were decreasing gradually over the western suburban areas during 2001-2013. Compared with the difference in the climate background between western suburban areas and the reference stations of Jiangshan and Nanhui during 1959-1978, the urban clusters expansion exacerbated the difference between the western suburban areas and the reference stations about 1.6 times for heat wave days, enhanced 34.4% for mean temperature and 41.7% for mean maximum temperature. On the basis of the surface temperature data from the Moderate-resolution Imaging Spectroradiometer (MODIS), the land surface warming cores have expanded westward about 32.8% and thus strengthened local heat waves. All the above results are conducive to assess the climate effects of the urban planning pattern with one center and four sub-centers over Shanghai in the near future.