城市化对浙江省夏季极端高温事件的影响

URBANIZATION EFFECTS ON OBSERVED CHANGE IN SUMMER EXTREME HEAT EVENTS OVER ZHEJIANG PROVINCE

基于夏季逐日最高气温和卫星遥感夜间灯光数据,分析了1971—2011年浙江省夏季极端高温事件的变化及其与城市化之间的联系。结果显示,过去41年浙江省绝大多数气象站点的夏季高温日数和高温度日数都呈现出增加的趋势,其中,环杭州湾城市群、温台沿海城市带和金华-义乌三大城市群地区的夏季高温日数和度日数的增加更显著;基于逐日气温95百分位数和35℃阈值两种高温日定义方法的研究结果相当一致,都表明由于城市热岛效应的存在,使得城市站比农村站具有更多的高温天数和更强的高温强度;进入21世纪,浙江省城市站相对于农村站的高温日数增加更显著,这与2000年以后城市化进程的加快密切相关。

The urban heat island （UHI） phenomenon,which is characterized by higher air temperature in densely built areas than that of the surrounding rural area,can be regarded as the most representative and documented manifestation of climate modification.Although the UHI is a well-documented phenomenon,relatively little information in the literature is available about its impact on summer extreme heat events.With global warming forecast to continue into the foreseeable future,extreme heat events are very likely to increase in both frequency and intensity.As UHIs are characterized by increased temperature,they can potentially increase the magnitude and duration of heat waves within cities.Based on daily maximum temperature records from 62 observation stations in Zhejiang Province from the period 1971-2011 and satellite-measured nighttime light imagery from the Defense Meteorological Satellite Program （DMSP） Operational Linescan System （OLS） during 1992-2010,we analyzed the change of summer extreme heat events and its association with the rapid urbanization process.The results could be concluded as follows：（1） Zhejiang Province has experienced rapid urbanization and a dramatic growth in urban areas in the past two decades,especially after 2000.（2） The summer mean maximum temperature and the 95th percentile of summer daily maximum temperature in most stations of Zhejiang Province have increased,with the most significant increase in the highly urbanized areas including the city belt around Hangzhou bay,Taizhou-Wenzhou and Jinghua-Yiwu city belts.（3） The hot days and hot day degrees,defined by both daily 95th percentile and the threshold of 35 °C,show that the UHI effect causes additional hot days and heat stress in urban stations compared to rural stations.The results in this study suggest that the heat island effect should be determined and incorporated in preparing high temperature forecasts.