The Effect of Urbanization on Maximum, Minimum Temperatures and Daily Temperature Range in North China
城市化对华北地区最高, 最低气温和日较差变化趋势的影响

A data set of 255 stations including all of ordinary and national basic/reference climatological stations of North China is used to investigate the influence of enhanced urban heat island effect on the observed surface air temperature records over North China. The stations are classified into five categories according to the population of residential areas near the stations and the meta-data of specific locations of the stations. They are rural, town, middle-size city, big city and metropolis. National stations including national reference and basic stations are as an independent category. The analysis shows that all of the categories undergo a warming in terms of annual mean temperature and annual mean minimum temperature, with the national stations and urban stations experiencing more than average increase in temperature. Little change can be found in annual mean maximum temperature. Urban stations generally witness a significant drop in annual mean diurnal temperature range. Urbanization effect is obviously reflected in annual and seasonal mean surface air temperature trends as obtained from the national stations and urban stations. The urban warming is more significant for annual mean temperature and annual mean minimum temperature for the urban and national stations, with the national stations undergoing an annual urban warming of 0.11℃·(10a)~(-1) and 0.20℃·(10a)~(-1), respectively. The contribution of the annual urban warming to the overall warming as observed from the national stations reaches 39.3% and 52.6%, respectively for annual mean temperature and annual mean minimum temperature. Wintertime registers the largest urban warming for seasonal mean temperature and minimum temperature, and the smallest urban warming is seen in summertime. Annual and seasonal mean daily temperature range of all categories of urban stations and national stations significantly decrease during the time period of 1961-2000, and the decrease is completely attributable to the urbanization effect. The drop of seasonal mean daily temperature range of the national stations for autumn and wintertime during the same period is also entirely caused by the urbanization effect.