In this paper, we examine the changing characters of extreme tropical precipitation based on simulations with of the Department of Energy (DOE), Exascale Energy Earth System Model (E3SM). AMIP-type experiments were carried out respectively for control (present-day SST and CO₂), P4K (+4K uniform SSTA, with present-day CO₂), and 4XCO2 (quadruple CO2 atmospheric forcing, and matching SSTA, based on CMIP6 ensemble coupled model projections). Top 5% (PCT05) and 1% (PCT01) rain intensity in the control are used as a metric to define extreme precipitation.

Results show significant increase in both convective precipitation (CVP) and stratiform precipitation (STP) as a function of rainfall intensity, with the STP increasing much more than CVP for extreme precipitation. Under P4K, and 4xCO2 respectively, the tropical warm pool (SST> 29^oC) expands substantially, covering nearly the entire tropics. Increase in extreme precipitation generally follows the paradigm of “wet-getting-wetter” and “warmer-getting-wetter”. PCT05 and PCT01 heavy rainfall are associated with strong radiation-cloud-convection-circulation interaction (R3CI), with increased contribution from STP. Four extreme precipitation regimes are identified:

• Open ocean: Increase in relative humidity (RH) near surface and lower-troposphere lead to increase in rainfall efficiency, i.e., more PCT05, PCT01 rainfall from warmer clouds (lower cloud top) over the ITCZ/SPCZ core, and expanded region with warmer SST (exceeding 29^o C) under P4K and 4xCO2.
• Continental land: Strong surface warming, reduction in surface RH, but with strong upper-level heating by LS precipitation, over the equatorial Africa, and the Amazon
• Maritime continent: Mixed behavior from ocean and continental land, including emerging signals of fixed anvil temperature (FAT) associated with extreme precipitation
• Asian monsoon region: By far, this region shows the strongest signal of increased contribution by STP and FAT, stronger in 4xCO2 then P4K, indicating importance of atmospheric heating by CO2 in amplifying effects of land-sea surface heating contrast.