Interdecadal Variation of the Temperature and the Impact of Urban Growth on the Temperature in Xi'an Region

The impact of urban growth on the temperature jump and the heat island in Xian region, China, has been investigated using temperature data measured at 14 observation stations from 1966 to 2005. The urban impact was stood for by the difference of average temperature between urban and suburban areas. The conclusions can be drawn as follows: 1) In summer and winter, the temperature temporal variation characteristics over suburbs,plain area,hill,are conformance with the regional average temperature,and represents the large scale climate characteristics,but small scale cimate variation characteristics are represented in urban region which is different with the areas mentioned above. But, there are different phases in the longterm change of the urban and regional average temperature, which has smallscale climate feature. 2) Xian region had a temperature increasing jump mainly with natural increase in the winter of 1977, somewhat earlier than the whole China, seven years earlier than Northwest China.The first summer temperature increasing jump appeared in 1988, five years earlier than Northwest China. 3) The effect of urban heat island was stronger in winter (0.65 ℃) than in summer (0.46 ℃). 4) In winter the average temperature increased 1.3 ℃ after the temperature jump in 1989, and the urban impact accounts for 0.35 ℃; In summer, the average temperature increased 0.4 ℃ after the temperature jump in 1987, and the urban impact accounts for 0.39 ℃. It indicates that the urban impact plays an important role in the temperature increase in summer. 5)The urbanization index, such as building proportion，the population of urban area and the quantity of the buses, and the variation of temperature are closely correlated. It can be concluded that the urbanization is the main reason for the temperature increase during the winters from 1989 to 1995, and the summers from 1987 to 1995.