More frequent, long-lasting, extreme and postponed compound drought and hot events in eastern China

As a result of global warming, compound extreme events become more frequent across the world. Compound drought and hot events (CDHEs) are receiving increasing attention because their social and environmental impacts are greater than those of individual extreme events. This study uses the standardized precipitation index (SPI) and maximum temperature, to define CDHEs based on the two-dimensional definition on the daily scale, in eastern China during the warm season (May - October) from 1961 to 2018, identify hot spot areas of CDHEs, and explore the multiple characteristics and variations of CDHEs. The main results are as follows: North China (NC) and Southwest China (SWC) were selected as hot spot areas due to their high-frequency of compound days and the increasing trend in the number of days and land area ratio affected by compound days. CDHEs have become more frequent, long-lasting and extreme in eastern China, especially in NC. Although the change in SWC is not as great as that in NC, the proportion of extreme events in all the severities and the proportion of long duration events in all the durations are larger in SWC than in the other regions. The probability distribution of occurrence date was unimodal in the entire eastern China and it was similar in NC. Whereas, the probability distribution was bimodal in SWC. The occurrence dates of CDHEs with different severities and durations postponed in 1991–2018 compared to 1961–1990, and this feature was the most pronounced in SWC. This study contributes to raising awareness of CDHEs and informs the mitigation of their adverse effects.