This is an open access article under the terms of the Creative Commons...

Dai, N., and B. Soden (2021), This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. Convective Aggregation and the Amplification of Tropi, AGU Advances, 1, e2020AV000201, doi:10.1029/2020AV000201.

It is widely believed that precipitation extremes will increase in response to a warming climate, as inferred from both observations and numerical simulations. In the absence of changes in atmospheric circulations, extreme precipitation is expected to increase in already‐moist regions along a thermodynamical Clausius‐Clapeyron scaling. However, within the tropics, the sensitivities inferred from observations of interannual variability are roughly twice as large, implying an unknown contribution from atmospheric dynamics. In this paper, we use satellite observations and climate model simulations to investigate the relationship between convective aggregation and precipitation and the role that convective aggregation plays in amplifying the response of tropical precipitation extremes to interannual surface warming. We find that the occurrence of heavier precipitation coincides with a higher degree of convective aggregation. Extreme precipitation events and convective aggregation tend to increase during warm, El Niño events compared to colder, La Niña events. Although both the frequency and intensity of heavy to extreme precipitation can increase with increased aggregation during El Niño, the changes in frequency are more consistent among the observations and models than changes in intensity. In both the observations and models, increases in large‐scale convective aggregation contribute to roughly one third of the increase in extreme precipitation frequency due to interannual warming by shifting moderate‐to‐heavy precipitation events to more extreme precipitation intensities. The linkages between convective aggregation and precipitation extremes considered here offer insights into their potential response to anthropogenic warming. Plain Language Summary As climate warms, one of the most prominent changes in the global water cycle is more common extreme rainfall events in the tropics. A mechanism that enhances the convection process and its related precipitation could increase the rate of occurrence and strength of these events rising with the temperature. Here, we investigate how a phenomenon known as convective aggregation contributes to more common tropical extreme rainfall events on a year‐to‐year basis. We find that heavier rainfall is closely tied to a more aggregated state of atmospheric water vapor. Both observations and models show that more extreme rainfall events and the aggregation of moisture occur during warm, El Niño events relative to colder, La Niña events. The enhanced aggregation process creates extra moisture in the already‐moist regions leading to more common heavier precipitation events and less common lighter precipitation ones. As a result, the increase in convective aggregation amplifies the increase in extreme rainfall events related to year‐to‐year surface warming by roughly one third. Our findings provide new insight on projections of future rainfall extremes, which have strong implications for disaster risk management.

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