An abrupt increase in the summer high temperature extreme days across China in the mid-1990s

Based on the daily maximum surface air temperature records from an updated homogenized temperature dataset for 549 Chinese stations during 1960--2008, we reveal that there is an abrupt increase in the number of days with high temperature extremes (HTEs, an HTE day is defined when the maximum temperature exceeds the 95th percentile of the daily maximum temperature distributions) across China in the mid-1990s. Before this regime shift, the average number of HTE days is about 2.9 d yr-1 during the period from the 1970s to the early 1990s, while it rocketed to about 7.2 d yr-1 after the mid-1990s. We show that the significant HTE day increase occurs uniformly across the whole of China after the regime shift. The observational evidence raises the possibility that this change in HTE days is associated with global-scale warming as well as circulation adjustment. Possible causes for the abrupt change in the HTE days are discussed, and the circulation adjustment is suggested to play a crucial role in the increase in HTE days in this region.