Extreme Tropical Precipitation Clusters Show Strong Increases in Frequency Under Global Warming in CMIP6 Models.

Precipitation clusters are spatially contiguous precipitating regions. Large clusters in the tropics are rare, extreme events that include organized precipitating systems. Changes to the probability distributions of tropical precipitation clusters under global warming are examined using models from the coupled model intercomparison project Phase 6 (CMIP6). Every analyzed model projects significant increases in frequencies of both very large‐sized clusters and clusters with very large area‐integrated precipitation (cluster power). The occurrence probability for the highest historical cluster power values increases by a factor between 4 and 15 among models in the end‐of‐century SSP5‐8.5 scenario. These changes primarily occur over the precipitating tropics: the western Pacific, Indian subcontinent, central and east Pacific convergence zones, and parts of South America. This spatial pattern is largely explained by Clausius‐Clapeyron scaling of current climate cluster power values. Societal impacts of cluster power increases could be acute in coastal regions of the Indian subcontinent and western Pacific islands. Plain Language Summary: Spatially continuous precipitating points are called precipitation clusters. In the tropics, the largest of these clusters represent systems like hurricanes or groups of thunderstorms. Large clusters also release greater rainfall and therefore hold more potential for destruction. In this study, we use state of the art climate models to examine how precipitation clusters with very large size and rain amounts will change under global warming. All the models we analyzed agree that there will be significant increases in the frequency of large and heavily precipitating clusters. The models project between a 4 and 15 times increase in the frequency of clusters bearing the largest rain amounts. These increases are projected to happen predominantly over tropical regions with warm surface waters. We also found a simple hypothesis that explains these changes. This hypothesis is based on the fact that warmer air can hold more moisture. Increases in the frequency of precipitation clusters with large rain amounts could be particularly devastating for the islands of the western Pacific and heavily populated coastal regions of the Indian subcontinent. Key Points: Probability distributions of precipitation clusters (contiguous precipitating regions) are reasonably reproduced in CMIP6 modelsUnder global warming, models project increases in frequencies of both clusters with large size and clusters with large precipitationThese increases primarily occur over tropical regions with a large incidence of heavily precipitating systems in current climate [ABSTRACT FROM AUTHOR]