The Response of Tropical Land-Ocean Precipitation Partitioning to SST and CO2 increase in Global Storm Resolving Simulations

In the tropics, the land-ocean precipitation partitioning χ is skewed toward land. We analyze how CO₂- and uniform sea surface temperature increase affect this partitioning. To do so, we use 15 years of global simulations conducted with the ICON model at 10 km horizontal grid spacing and explicitly resolved convection, unlike previous studies that parameterized convection. ICON produces a precipitation partitioning that is more consistent with observations compared to the AMIP6 ensemble. Under 4xCO₂, precipitation partitioning toward land increases, whereas it decreases in +4K. We develop a framework based on energy and moisture budgets to decompose the response of the precipitation partitioning into contributions from the land column-integrated atmospheric heating, circulation efficiency, moisture cycling, and tropical radiative cooling. In ICON and the AMIP6 ensemble, the land's column-integrated atmospheric heating is identified as the primary driver of changes in precipitation partitioning. This is a result of the change in land moisture convergence and land precipitation in response to circulation adjustments driven by land-sea asymmetries in atmospheric heating. The response of the controlling factors are similar in ICON and in the AMIP6 ensemble, apart from two qualitative differences. First, the land's circulation efficiency is more stable in ICON than in AMIP6, which we interpret to be due to a stronger coupling of precipitation to surface heat fluxes in AMIP6. Secondly, the opposing response in χ  upon 4xCO₂ and +4K are virtually equal in magnitude in ICON, whereas in AMIP6 χ decreases more in +4K than it increases in 4xCO₂. These findings suggest that coarse-resolution GCMs may overestimate the predicted decrease in land precipitation under global warming.