Spatial and temporal features of summer extreme temperature over China during 1960–2013

Based on daily air temperature data from 772 stations in China, the present study uses absolute index and percentile index to investigate the spatial and temporal features of summer extreme temperature over China during the period 1960–2013. The analysis indicates that Xinjiang and southeastern China are two major domains where extreme heat events frequently occur and that the number of heat day (NHD) and the frequency of heat wave (FHW) both show an increasing trend throughout the country except for Shandong and Henan provinces where a decreasing trend is identified. Although the two leading empirical orthogonal function (EOF) modes of the NHD and the FHW based on the absolute index and percentile index have differences, the time series of the first principal components (PC1) are consistent; PC1 depicts opposite trends from 1960 to late 1990s and during the late 1990s to 2013. According to the climatology and EOF modes, four sub-regions are chosen: Chuanyu, Huanghuai, Southeast, and Xinjiang area. The inter-decadal variation over the four sub-regions differs, but the NHD and the FHW significantly increase after the mid-1990s. Based on Mann-Kendall method, it is found that the NHD and the FHW over Chuanyu exhibited abrupt shifts in 1978 and 2000; sudden shifts occurred in 1973 and 2000 over Huanghuai; an abrupt shift occurred over the Southeast area in 2003.