Changes in the Observed Trends in Extreme Temperatures over China around 1990

Based on the daily temperature data from weather stations in China, linear trends of the seasonal mean and extreme temperatures in summer and winter are analyzed and compared for the periods of 1960-89 and 1990-2009. The results show prominent changes in those trends since the early 1990s, in particular in winter a signal of climate shift as previously identified. The changes, however, are found to be strongly region dependent. In summer, both seasonal mean and extreme temperatures show a considerable cooling trend in central China and a warming trend in north and south China before 1990. After 1990 all temperature indices show significant warming trends throughout China with the largest trend up to 4.47 degrees C (10 yr)(-1) in north China. In winter in north China, with the most prominent warming trend during 1960-89, there is a significant cooling trend in both the seasonal mean temperature and the cold temperature indices after 1990. The warming trends over the Tibetan Plateau are substantially enhanced since 1990. All indices for the diurnal temperature range (DTR) show consistent decreasing trends in both summer and winter throughout China before 1990 while they turn to increasing trends in northeast China in summer and over the Tibetan Plateau in winter after 1990. The annual temperature range displays a decreasing trend throughout China before 1990 while it is dominated by an increasing trend after 1990 except over the Tibetan Plateau and in a narrow band along the Yangtze River. Possible mechanisms for the observed trend changes are discussed.