Change of Urban Heat Island Intensity and Its Effect on Surface Mean Air Temperature Records in Southwest China

The surface air temperature records are obviously affected by the urbanization in China.The changes of the surface air temperature in Southwest China lag behind the countrywide changes, and air temperature records at some stations even show a dropping trend.It is important to understand the detailed features of surface air temperature change trends and the effect on them of urban development for different stations in that region.Using a data set of monthly mean temperature from 322 stations and corresponding population data, the surface air temperature change trends and the effect of urbanization development on mean surface air temperature records in towns and cities in Southwest China during 1961—2004 are analyzed.Quality control and inhomogeneity adjustment are made for air temperature data.On the basis of calculating air temperature change trends of towns and cities at national reference/baseline stations and rural stations, the extent and relative contribution proportion of urbanization effect are obtained by comparing the differences between the change trends of various stations and rural stations.Results show that there are warming trends of surface air temperature for each of the station groups.The warming rates in towns and cities, and national stations are greater than those in rural areas.In annual mean surface air temperature records in towns and cities, and national stations, urban warming rates are estimated as 0.086 ℃/10a and 0.052 ℃/10a respectively, and their contributions to overall annual mean temperature change are 57.6% and 45.3% respectively.Compared with the other regions in China, the warming rates of temperature and the urban warming rates in Southwest China are relatively low.Although the change of the average heat island intensity in this region is smaller than those in quite a number of regions in China, the contributions of urban warming to the overall mean temperature change trends are generally larger as a result of this feature.In addition, there are obvious season changes in urban warming rates, with the urban warming rates in autumn, spring or winter being the largest and second respectively, and that in summer the smallest. However, the largest contributions (100%) of urban warming to mean temperature in seasons are in spring, second to which are the contributions in summer of 73% and above.Those in autumn and winter are relatively smaller.