The Indo‐Pacific Rim at Risk: How Rossby Waves Contribute to Extreme Precipitation Clustering

Clustering extreme weather events are concurrent or consecutive occurrences of disastrous weather in multiple regions, resulting in cumulative impacts. Here we discovered a significant increasing trend in clustering extreme precipitation events over the Indo‐Pacific rim over the past four decades. This trend can be largely attributable to the increasing frequency of the Rossby wave response, including the circum‐Pacific and cross‐Pacific patterns due to Rossby wave activity propagation, and the Pacific anticyclone pattern due to Rossby wave breaking. The three patterns show remarkable disparity in seasonality, persistence, and hydrological impacts. They can increase the occurrences of most severe precipitation by up to 5, 8, and 25 times, respectively. The Indian Summer Monsoon heat sources and La Niña are identified as key drivers, and the mid‐latitude jet streams are modulators contributing to the events. Our findings suggest that specific Rossby wave patterns may influence the potential evolution of future clustering extremes. Plain Language Summary Extreme precipitation events that occur concurrently or consecutively in multiple regions over a period, can have a cascading effect on human livelihoods. This is a new type of disastrous weather event in the context of climate change, which we call clustering extreme precipitation events. However, there is a lack of understanding about their frequency and underlying mechanisms. To address this, we propose an identification method for clustering extreme precipitation events over the Indo‐Pacific Rim. Here, our findings reveal that three distinct Rossby wave patterns are responsible for these events. Accompanied by more frequent occurrence of the identified Rossby wave patterns, the frequency of clustering extreme precipitation events has increased (0.5 event/decade) in the past 42 years. The Rossby wave patterns set up favorable atmospheric conditions and significantly increase the occurrences of the most severe precipitation in the Northern Hemisphere. The Indian Summer Monsoon heat sources serve as a first‐order driving mechanism for exciting the Rossby waves, while La Niña serves as external forcing. Additionally, the variations of mid‐latitude jet streams modulate the development of the Rossby wave patterns. The results provide a predictability source for the sub‐seasonal to seasonal community. Key Points Over the past 42 years, there has been an increase in the frequency of clustering extreme precipitat