First introduced by the IPCC in 2012, compound weather events refer to combinations of multiple climate drivers and hazards that interact to create amplified societal and environmental risks. Unlike isolated extreme events, these overlapping phenomena involve a complex interplay of factors, leading to impacts that are far greater than the sum of their parts. As global temperatures rise, the frequency and severity of compound events are expected to increase, making them a critical area of study. Research in this field focuses on understanding the mechanisms behind these interactions to improve predictions, assess cascading impacts, and develop strategies for detection, mitigation, and adaptation.

Typologies and Their Cascading Impacts

Temporally compounding events involve successive hazards occurring in the same geographical area. In California, for example, heatwaves followed by droughts significantly elevate wildfire risks. Research shows that wildfires are 62% more likely during such events compared to droughts alone and 26% more likely than during isolated heat events. This heightened risk extends beyond traditional wildfire seasons, with compounded conditions leading to a 75% increase in wildfire frequency during fire seasons and a 71% rise outside of it.

Multivariate compounding events, on the other hand, involve the simultaneous occurrence of multiple hazards within the same region. A key example is the co-occurrence of drought and heat during wheat flowering periods. This combination was shown to drastically reduce agricultural yields, with a 70% chance of below-average production during such events. In comparison, isolated droughts or heat events resulted in only a 50% probability of reduced yields. Median wheat yields during compounded events were 7% below average, while isolated hazards led to modest increases.

Spatially compounding events occur when a single hazard affects multiple, connected regions. The study examined the influence of climate modulators like the El Niño–Southern Oscillation (ENSO) and the Atlantic Multidecadal Oscillation (AMO) on tropical cyclone activity. ENSO was found to intensify cyclones in the Pacific while suppressing them in the Atlantic, whereas AMO had the opposite effect.

Preparing for a Future of Compounding Risks

Looking ahead, climate models project a significant rise in the frequency and intensity of compound weather events. Under a high-emission scenario (SSP5-8.5), the likelihood of temporally compounded events in California is expected to increase by 9% by mid-century. These changes could extend wildfire seasons, exacerbate agricultural stresses, and intensify tropical cyclones, with far-reaching consequences for ecosystems, infrastructure, and communities.

The study underscores the importance of developing integrated approaches to address the challenges posed by compound events. Improved predictive models and interdisciplinary research are essential to understanding the cascading impacts of these phenomena. Furthermore, proactive adaptation strategies—ranging from wildfire management to climate-resilient agriculture—are critical for mitigating risks.