Effects of Urbanization in Northern China on Extreme Winter Minimum Temperatures

This paper examined the urbanization impact on extreme winter minimum temperatures from 33 stations in North China during 1957-2010. The population and station metadata, satellite-measured nighttime light intensity and MODIS land cover map are firstly used as three urbanization indices to classify the stations into urban and rural ones, and the classification differs by the different indices among these indices. We then used the Generalized Extreme Value (GEV) distribution to analyze the distribution of extreme minimum temperatures and the long term variations of the three distributional characteristics parameters. Results suggest that among the three extreme minimum temperature distribution parameters, the position parameter is the most representative in terms of its long term change. A new classification method based on the intercommunity (factors analysis method) of the temperature change is developed to detect the urbanization effect on winter extreme minimum temperatures in different cities. During the period of rapid urbanization (after 1980), the magnitude of variations of the three distribution parameters for the urban station group is larger than that for the reference station group, indicating a higher chance of occurrence of warmer weather and a larger fluctuation of temperatures. Among different types of cities, the three parameters of extreme minimum temperature distribution of the urban station group are, without exception, higher than those of the reference station group. The urbanization of different types of cities all show a urban heat island effect, with small-size cities have the most evident effects on extreme minimum temperatures.