Regional Analysis of Precipitation in a Community Atmosphere Model (CAM6) Perturbed Physics Ensemble (PPE)

Climate simulations and projections of regional rainfall are important to society, and climate models are one important tool used for such projections. However, because of uncertainties in small-scale physics processes that differ from one region to another, climate models often perform better in some areas relative to others. In order to understand climate model regional projection skill, we need to better understand their present-day rainfall simulation performance across a variety of regions spanning Earth. To begin understanding regional skill, we analyzed a Perturbed Physics Ensemble (PPE) of the CESM2-CAM6 model, and specifically compare the PPE members' rainfall simulations with each other and against ERA5 reanalysis, for five different types of rainfall regimes (as well as globally). We determine which PPE members most skillfully simulate the diverse regimes. The physics parameter settings associated with each of these members are compared to the CAM6 default values to determine whether some parameters exclusively push in one direction relative to the default settings. Our results could inform decisions regarding future parameter auto-calibration efforts in the CESM-CAM model, thus potentially aiding in climate model tuning efforts and possibly enabling improved skill in the model's hydrologic cycle prediction.