Amplification of non-stationary drought to heatwave duration and intensity in eastern China: Spatiotemporal pattern and causes

Amplifying the frequency and loss of weather and hydrological extremes under climate warming have aroused increasing human concerns in recent decades and it is particularly the case for compound drought-heatwave (CDH) events. The drought index based on the hypothesis of non-stationarity is of great significance for the study of CDH events. Here we presented spatiotemporal patterns of CDH, general heatwaves (GHW, he heatwave that does not occur in dry months) and relevant circulation backgrounds in eastern China. We found that heatwaves are starting earlier and ending later and later. While, the termination date of heatwaves in southern China is late than those in northern China. Significant increases since the 1980 s were detected in the frequency, duration, and intensity of heatwaves and the frequency of CDH events in eastern China. Besides, heatwaves were observed mainly in the middle and lower Yangtze River basin and in the Sichuan Basin as well. Most areas of eastern China were dominated by higher occurrence probability of CDHs in July and the probability was as high as 0.49. The duration and intensity of the CDHs were 0.28 days longer and 11.14℃ higher than GHWs. Further examinations show that the western Pacific subtropical high (WPSH) has a significant influence on the occurrence of heatwaves. The average position of the WPSH is shifted westward and its intensity is relatively stronger, thus favoring the occurrence of heatwave events. The occurrence of compound events in eastern China cannot be separated from the influence of large-scale circulation and atmospheric changes.