Dependence of compound hot and dry extremes on individual ones across China during 1961–2014

Compound hot and dry extremes have drawn extensive attention given the devastating impacts on natural ecosystem and social economy. However, the substantial dependence of compound hot and dry extremes upon individual ones is barely discussed at the daily level. In this study, we present the dependence of compound hot and dry days (CHDDs) and events (CHDEs) upon individual ones using summer (June–July–August) daily temperature and precipitation across China during 1961–2014. Results show more CHDDs and CHDEs over regions from northeast to southwest China, with stronger intensity over the transitional area between Northwest China (NW) and the Tibetan Plateau. Simultaneously, the period with the occurrence of compound extremes generally extends since compound extremes start earlier and end later. On average over China, hot extremes are significantly (p < 0.01) influential on the frequency (r = 0.42–0.83) of compound extremes, which contribute 55–78% to changes in the frequency. Dry extremes are significantly (p < 0.01) influential on the intensity (r = 0.60–0.79) and contribute 63–70% to changes in the intensity. Both hot and dry extremes are influential on the start and end of compound extremes. More importantly, largely influenced by the high probability of dry extremes in North China, the joint probability of compound extremes is higher in NW followed by Inner Mongolia. These findings highlight the new insights into compound extremes defined by relative thresholds at the daily level.