超大城市热岛效应的季节变化特征及其年际差异

Study on seasonal variations of the urban heat island and its interannual changes in a typical Chinese megacity

本文以超大城市上海为例,分析了近50年四季城郊温差的总体变化趋势,同时利用城市化进程中4个年份(1987、1990、1997和2004年)9个气象站的气温数据,重点研究了上海地区热岛效应的季节变化特征及年际差异.结果表明,近50年来上海城郊温差逐年显著增长,年平均热岛天数频率为86.0%,年平均热岛强度为1.17℃,秋季热岛频率和强度高于其他季节,累积热岛强度也最大.不同时刻热岛的特征表明,夜间热岛(2∶00,20∶00时刻)累积强度在四季都较大,在春、夏季14∶00时刻热岛累积强度较大,而在秋、冬季8∶00时刻热岛累积强度较大.进一步分析表明,热岛效应的四季差异主要在于较强热岛和强热岛出现频率的差异;秋季大气最稳定的F类型比例较高可能是热岛效应更加显著的原因之一.四个年份对比分析表明,1997年之前的三个年份,热岛效应的四季差异比较显著.之后,随着年代的推移,四季累积热岛强度逐渐趋于均化,并且夏季低强度热岛有向中强热岛和强热岛转化的趋势,一定程度上反映了夏季人为热的贡献.

The differences between the urban and rural temperatures in the past 50 years were analyzed based on the seasonal averaged data from 1960 to 2006 at two meteorological stations in Shanghai megacity.Moreover,the characteristics of the urban heat island（UHI） in Shanghai for the last two decades were studied based on air temperatures measured four times per day at nine stations in 1987,1990,1997 and 2004 in urbanization process.The corresponding seasonal variations of UHI in Shanghai were discussed.The results showed that the temperature differences between urban area and suburb were increasing in fluctuations,UHI occurred in 86.0% days of a year with an average magnitude of 1.17 ℃,and the frequency and magnitude of UHI in autumn were higher than those in other seasons,with the highest accumulated UHI.The accumulated intensities of night-time UHI（2 ∶ 00,20 ∶ 00） were significant in all four seasons,but that at 14 ∶ 00 were more significant in spring and summer,and that at 8 ∶ 00 is more evident in autumn and winter.It can be inferred that the seasonal variations could mainly be attributed to the frequency difference between mid-intensity UHI and high-intensity UHI.Besides,the F-level stability condition occurred more frequently in autumn,which could account for the enhancement of autumn UHIs.Also the differences among 4 years were discussed.The accumulated intensity of UHI was the strongest in autumn,while weakest in summer before 1997.However,the accumulated intensities of UHI of four seasons tended to be equalized during 1997—2004.In summer,low-intensity UHI tended to change into mid-magnitude and high-magnitude UHI,which could be caused by anthropogenic heating in some degree.