Changes in Seasonal Cycle and Extremes in China during the Period 1960-2008

Recent trends in seasonal cycles in China are analyzed, based on a homogenized dataset of daily temperatures at 541 stations during the period 1960-2008. Several indices are defined for describing the key features of a seasonal cycle, including local winter/summer (LW/LS) periods and local spring/autumn phase (LSP/LAP). The Ensemble Empirical Mode Decomposition method is applied to determine the indices for each year. The LW period was found to have shortened by 2-6 d (10 yr)(-1), mainly due to an earlier end to winter conditions, with the LW mean temperature having increased by 0.2 degrees C-0.4 degrees C (10 yr)(-1), over almost all of China. Records of the most severe climate extremes changed less than more typical winter conditions did. The LS period was found to have lengthened by 2-4 d (10 yr)(-1), due to progressively earlier onsets and delayed end dates of the locally defined hot period. The LS mean temperature increased by 0.1 degrees C-0.2 degrees C (10 yr)(-1) in most of China, except for a region in southern China centered on the mid-lower reaches of the Yangtze River. In contrast to the winter cases, the warming trend in summer was more prominent in the most extreme records than in those of more typical summer conditions. The LSP was found to have advanced significantly by about 2 d (10 yr)(-1) in most of China. Changes in the autumn phase were less prominent. Relatively rapid changes happened in the 1980s for most of the regional mean indices dealing with winter and in the 1990s for those dealing with summer.