Change in extreme temperature event frequency over mainland China, 1961−2008

Based on homogeneity-adjusted daily temperature data from national stations, the spatial and temporal change in extreme temperature events in mainland China have been analyzed for the period 1961-2008. The analysis shows that the numbers of frost days and ice days were significantly reduced, with the most significant reduction generally in northern China for ice days but more extensively across the country for frost days. Summer days and tropical nights significantly increased along the middle and lower reaches of the Yangtze River and in southern Southwest China. The maximum values of T max (TXx) and T min (TNx) and the minimum values of T max (TXn) and T min (TNn) generally rose, and TXx and TNx significantly increased in northern China, while TXn and TNn significantly increased across the whole country. A significant reduction at a rate of -8.23 d decade -1 (-3.26 d decade -1 ) occurred for cool nights (days), and a significant increase at a rate of 8.16 d decade -1 (5.22 d decade -1 ) occurred for warm nights (days). The reduction of cool nights and cool days occurred mainly in winter, but the increase of warm days and warm nights occurred mostly in autumn and summer. Extreme cold indices were reduced, mainly after the mid-1980s, while extreme warm indices increased remarkably after the mid-1990s. The analysis also shows that, for North China, the urbanization effect on the series of extreme temperature indices was statistically significant for the negative trends of frost days, diurnal temperature range, cool nights and cool days, and for the positive trends of summer days, tropical nights, TNx, TNn, and warm nights.