Spatial and Temporal Features of Spring Extreme Low Temperature Events in China during 1961–2016

Based on daily minimum temperature data from 529 stations in China for the period 1961–2016, in this study, we investigated the spatio-temporal features of spring extreme low temperature (ELT) events. The results of our rotated empirical orthogonal function (REOF) analysis indicates that, with respect to the variability of the spring ELT events frequency, China can be divided into five regions, including Northeast China–eastern North China, the Jiangnan region, eastern Northwest China–western North China, Southwest China, and northern Xinjiang. The results of our Morlet wavelet analysis indicate that the spring ELT events frequencies over the five regions exhibit a 2–4-year quasi-periodicity. This 2–4-year quasi-periodicity is significant over the whole period for the Jiangnan region, eastern Northwest China–western North China, and northern Xinjiang; over the period prior to the early 1980s for Northeast China–eastern North China; and over the period between early 1980s and mid-1990s for Southwest China. With respect to long-term variation, the spring ELT events frequencies over all five regions exhibit decreasing trends, although the years of their abrupt change differ. The results of our Mann–Kendall analysis and moving t-test suggest that the abrupt change in the spring ELT events frequency occurred in 1987/1988 for Northeast China–eastern North China, 1995/1996 for the Jiangnan region, 1990/1991 for eastern Northwest China–western North China, 1987/1988 for Southwest China, and 1997/1998 for northern Xinjiang. Along with the decreasing spring ELT events frequency, the spring ELT events intensities have weakened in the five regions in the past half century. However, in the past 10 years, the spring ELT events frequency and intensity over eastern China have increased, which merits concern.