Variation of Frost Days and Its Relationship to Regional Warming in Northern China

Based on daily mean temperature data from 62 stations of northern China since 1951, the trend of frost days and temperature has been analyzed, and the variation trend of the starting date in autumn and the ending date in spring have been shown. The results indicate an obvious reduction trend of frost days, an increase trend of frost-day temperature in northern China from 1951 to 2000, and the increasingly longer growth season due to early start date of spring and late ending date of autumn. We can also find a good relationship between frost-day temperature and mean temperature in the period, this may foreshow the variation of mean temperature is produced by frost-day temperature.