The evolution of the frequency of dry/wet spells is a hot topic in global climate change research. The synergistic effects of dry/wet spells make their consequences far more significant than a single disaster, having considerable impacts on hydrology, ecology, and economies, especially in the context of global warming. In this study, the standardized precipitation evapotranspiration index (SPEI)-based identification of dry/wet spells was used to explore the evolution of the frequency of dry/wet abrupt alternation (DWAA) events in the past four decades in China, makes up for the lack of research on the evolution of such compound disasters. China has been affected by dry/wet spells in many areas for a long time. Studies found that high-frequency DWAA areas are concentrated in densely populated areas, China's essential food bases and core areas for economic development. Dry-to-wet (D-W) events and wet-to-dry (W-D) events basically increased or decreased at the same pace in this period. We innovatively find DWAA events (D-W events and W-D events) are projected to occur increasingly in a wider region of China. The frequency of D-W events across China has increased from 2.35 in the 1980s to 3.56 in the last decade, a 50% increase. On the other hand, W-D events increased from 2.6 to 3.23, increasing 24%. The three regions with the most remarkable changes in the past four decades are Inner Mongolia, northwest China, and north China, where D-W events increased by 121, 61, and 58%, respectively, and W-D events increased by 71, 57, and 61%, respectively. Hereby, it is vital to implement effective prevention against DWAA events in the area which has been neglected in the past decades because of lower frequency. These results may help policymakers develop suitable disaster mitigation plans for reducing the potential risks of extreme compound natural events.

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Tropical cyclone disasters frequently occur in the southeastern coastal areas of China, and the concentration of population and economy has further increased the risk of tropical cyclone disasters in this region. The effects of tropical cyclones on populations involve a complex interaction between hazard intensity, environmental factors, exposure level, and fortification capacity. Therefore, quantifying the relationship among these factors is imperative for early warnings, risk assessments, and mitigation strategies for tropical cyclone disasters. In this study, a comprehensive tropical cyclone quantitative risk assessment approach considering the joint relation between strong wind and extreme precipitation and environmental, exposure and fortification factors was developed using the generalized additive model (GAM) and copula function for the case of Hainan province, China. The 10 min maximum wind speed (MW), maximum daily rainfall (MR), elevation (ELE), total population (POP), and time (t) were ultimately selected by the GAM as explanatory variables for the affected population rate (APR). A 50% increase in the MW produced a 48.779%–82.657% increase in the APR, a 50% increase in the MR produced a 19.534%–25.631% increase in the APR, and a 50% increase in the POP produced a 0.796%–15.193% decrease in the APR. The APR obviously increased with the return period increase in Hainan province. The APR of cites (counties) ranged from 0.443 to 0.632 for a once‐in‐10‐year return period and ranged from 0.518 to 0.829 for a once‐in‐50‐year return period.

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The impact of tropical cyclones is expected to worsen with continued global warming and socioeconomic development. Quantifying population exposure to strong winds and heavy rainfall induced by tropical cyclones is a core element of tropical cyclone population risk assessment. Based on the demographic dataset of Shared Socioeconomic Pathways and future tropical cyclone data, we first calculate and analyze the changes in impact frequency and population exposure to four tropical cyclone scenarios in the Northwest Pacific over the period 2015–2050. Then, we quantitatively assess the contribution rates of climate change, population change, and their joint change to population exposure change. The results show that East China, South China, and Southeast China are the areas with high exposure change. Additionally, most of the high exposure changes (absolute changes over 400,000 people) are significant, and primarily influenced by the changes in local population growth. Overall, exposure change in the Northwest Pacific is mainly influenced by climate change, followed by population change and joint change.