The Study on Urban Climate of Lanzhou

Based on the meteorological data sequence of Lanzhou city and circumjacent regions, and experimental data in urban area, data of climate factors were analyzed. The results are as follows: Temperature variation is divided into three stages in near 70 years; the early 1950´s and the early 1980´s are the jump points of Lanzhou urban climate during this period. The urban climate effect was analyzed by the difference of each climate factor between Lanzhou city and suburb. According to statistical data, three types of temperature differences show ascending trend from 1960 to 2000. These indicate that urban heat island effect becomes strong gradually. Annual precipitation difference decrease gradually from 1980, there is no rain island effect. Relative humidity in urban area declines gradually, and appears urban dry island effect from 1978. The overlap-add and weakening effects of mountain - valley breeze and heat island circumfluence affect wind speed in Lanzhou. It also displays that the thermodynamic property of urban underlying surface and the urban anthropologic heat have played an important role in urban climate effect.