兰州市近50年城市热岛强度变化特征

Characteristics of Urban Heat Island over Lanzhou in Recent 50 Years

利用1956-2005年兰州市日平均气温、日最高气温和日最低气温,分析了近50年兰州市城市热岛效应变化,并利用城区和郊区3种气温的倾向率计算了城市热岛强度倾向率和热岛增温贡献率。结果表明：1956-2005年兰州市3种气温的城郊差均呈逐年上升趋势,平均气温、最高气温和最低气温的倾向率分别为每10年0.371℃、0.169℃和0.654℃,其中,最低气温的城郊差上升最明显。近50年兰州市增温主要发生在后25年（1981-2005年）,前25年除城区最低气温外基本上以降温为主。后25年中,城区年平均气温、最高气温和最低气温倾向率分别为每10年0.789℃、0.997℃和0.625℃,郊区则相应为每10年0.493℃、0.790℃和0.077℃,其中最高气温增温最显著,最低气温增温最少;以年平均、最高和最低气温表示的城市热岛强度的倾向率分别为每10年0.395℃、0.188℃和0.674℃,热岛效应对城区增温的贡献率分别达到87.0%、49.6%和100%。冬季城市和郊区的平均气温和最低气温倾向率最大,但热岛增温贡献率最大的是春、夏季气温,而不是冬季气温;这可能主要与兰州市冬季严重的空气污染有关, 因为其对城市热岛有一定的抑制作用。20世纪80年代以后兰州市热岛效应有增强的趋势，但平均气温和最高气温的热岛增温贡献率除个别季节外有所下降。

The urban heat island effect in Lanzhou is analyzed using the average temperature and daily maximum/minimum temperature data from 1956 to 2005. The tendencies and contribution rates of heat island intensity are calculated using the temperature tendencies of the three temperatures of Lanzhou and the suburbs. Results show that the differences of the three temperatures between Lanzhou and the suburbs all exhibit increasing trends. The tendencies of average temperature, maximum temperature and minimum temperature are0.371 ℃/10a, 0.169℃/10a and 0.654 ℃/10a, respectively, with minimum temperature increasing most obviously. In recent 50 years, the temperatures increased mainly in the later 25 years （1981 to 2005）, and the tendencies of average temperature, maximum temperature and minimum temperature of Lanzhou are 0.789 ℃/10a, 0.997 ℃/10a, and 0.625 ℃/10a, while those of the suburbs are 0.395 ℃/10a, 0.188 ℃/10a, and 0.674 ℃/10a, respectively. The heat island contribution rates of three temperatures are 87. 0%, 49. 6%, and 100%, respectively. In winter, the tendencies of average temperature and minimum temperature are the greatest in both urban and suburb areas, but the heat island contribution rates of the temperatures are not the largest, which may be mainly related with the scvere air pollution in winter in Lanzhou, because it can hold back the urban heat island effect in some extent. In the later 25 years, the urban heat island effect of Lanzhou is becoming stronger, but the contribution rates of average temperature and maximum temperature are declining.