Abstract: Temporal changes in air temperature and urban heat island (UHI) effects during 1956-1998 were compared between a coastal city, Ji’nan, and an inland city, Xi’an, which were similar in latitude, size and development. During 1956-1978, except that the annual mean minimum temperature in Ji’nan increased by 0.37 ℃·10 a^-1. the temperature variables in the two cities did not display any apparent  trend. During 1979-1998, all temperature variables of the two cities showed an increasing trend. Comparing with that in Ji’nan, the increasing rate of annual mean maximum temperature and annual mean temperature in Xi’an was greater, but that of annual mean minimum temperature was smaller. In the two cities, heat island effect occurred during 1956-1978 but without any apparent trend, whereas during 1979-1998, this effect increased with time, especially in Xi’an where the annual mean minimum temperature and annual mean temperature increased by 0.22 ℃·10 a^-1 and 0.32 ℃·10 a^-1, respectively. Both the level and the interannual variation of the heat island effect were much greater in Ji’nan than in Xi’an, but the increasing rate of this effect was greater in Xi’an than in Ji’nan. Obvious differences were observed in the increasing rate of annual mean maximum air temperature, annual mean air temperature, and annual mean minimum temperature as well as the heat island effect in Ji’nan, whereas negligible differences were found in Xi’an. Among the three temperature variables, annual mean minimum temperature displayed the most obvious increasing trend and was most affected by heat island effect, while annual mean maximum temperature was most variable inter-annually. Geographical location not only affected the magnitude of urban warming, but also affected the mode of urban warming and the strength of heat island effect.

Key words: urban warming, heat island effect, annual mean air temperature, land uses, Hood infiltrometer, hydraulic properties, macroporosity.