Changes in compound temperature and precipitation extremes from combined effects of multiple circulation factors over China

Compound climate extremes, such as the occurrence of extreme temperature and precipitation events, exert a significant impact on the society and ecosystems. However, the analyses of compound climate extremes are rather lacking relative to climate extremes defined for a single climatic factor. This study investigates the spatiotemporal variations of the frequency in compound extremes including wet/warm (WW), wet/cold (WC), dry/warm (DW) and dry/cold (DC) for 1961-2020 in China. In particular, using the bivariate and multiple wavelet coherence analysis, a novel method for detecting the relationship between two variables, the individual and combined effects of atmospheric circulation factor(s) on compound extremes are investigated for different timescales. The results show that there is a remarkable upward trend in the frequency of compound WW and DW extremes for both warm (0.10 and 0.08 events/decade) and cold seasons (0.08 and 0.05 events/decade) in China, especially in the Tibetan Plateau and Northwest China, while a downward trend in compound WC (-0.03 and -0.02 events/decade in warm and cold season, respectively) and DC (-0.01 and -0.01 events/decade in warm and cold season, respectively) extremes for the period 1961-2020. AMO (Atlantic Multidecadal Oscillation) has the most significant positive/negative correlation with the frequency of warm/cold related combinations over most regions during the warm season. Multiple circulation factors can combine to simultaneously influence compound temperature and precipitation extremes, but their effects vary with time scales. Results of this study will provide a better understanding of the mechanism of the compound extremes and thus propose adaptive strategies.