Aquaplanet Hydrologic Cycle Sensitivities to Model Configration in Present and Future Climates

Aquaplanet configurations are a fundamental component within a climate model hierarchy. They reduce complexities of the Earth system while maintaining a reasonable resemblance to Earth’s climate and thus can reveal intrinsic properties of global circulation and precipitation. In this project, we leverage the Community Atmosphere Model (CAM) aquaplanet framework to explore sensitivities of the hydrologic cycle to model configuration in both present-day and global warming climate settings. We seek to better understand the response of the hydroclimate and precipitation statistics to choice of model physics (CAM4, CAM5, and CAM6), horizontal grid resolution within a limited range (2° and 1°), and ocean type (fixed-SST or slab ocean) in the present-day climate. These baseline model configuration sensitivities provide useful context in a subsequent examination of hydroclimate responses from a series of global warming simulations adapted from the Coupled Model Intercomparison Project Phase 6 (CMIP6) Diagnostic, Evaluation, and Characterization of Klima (DECK) protocol. Results based on present-day simulations indicate large sensitivities of tropical precipitation distribution to choice of grid resolution, with the nature of the response being physics-dependent. Such results may have important implications for the interpretation of precipitation distributions and extremes in projections of future climate.