The North American CORDEX-CMIP6 WRF evaluation run: comparing historical simulations from 25 km to convection-permitting scales

Abstract

Earth system models (ESMs) provide essential insight into large-scale climate variability and change but often lack the spatial resolution required to represent fine-scale processes critical for regional impacts and adaptation planning. To help address this gap, we present an updated high-resolution regional climate simulation for North America (NA) as part of the Coordinated Regional Downscaling Experiment (CORDEX). We evaluate a new reanalysis forced NA-CORDEX simulation at 12 km resolution against observational datasets, an earlier NA-CORDEX CMIP5 simulation (25 km), and the convection-permitting CONUS-404 simulation (4 km). Through these comparisons, we assess how horizontal resolution and regional model configuration influence historical differences from reanalysis and the representation of extremes, with a particular focus on precipitation processes given that convection is parameterized at 12 km. Relative to previous NA-CORDEX-CMIP5 simulations, the new CMIP6-based evaluation run reduces mean differences in temperature and precipitation compared to reanalysis and other observationally based datasets, improves the magnitude and timing of the diurnal precipitation cycle across North America, and substantially improves the representation of tropical cyclone structure and intensity. Notably, extreme precipitation rates are well captured at 12 km when compared to the convection-permitting simulations. While long-term convection-permitting climate simulations remain a key objective for regional modeling, the current generation of CORDEX simulations provides a practical balance between computational efficiency and physical realism for continental-scale climate assessment.