EVALUATING A VARIABLE-RESOLUTION APPROACH FOR SIMULATING WATER ISOTOPES IN THE CONTINENTAL UNITED STATES USING VR-ICESM

The reliability of global climate simulations, particularly in regions with complex terrain, is greatly limited by the model resolution, yet increasing the resolution of climate simulations comes with a high computational cost. Variable-resolution climate models offer a computationally cost-effective approach to resolving fine-scale regional topography compared to analogous uniform high-resolution simulations and have shown crucial enhancements in regional precipitation and temperature compared to analogous uniform low-resolution simulations. Nevertheless, a variable-resolution climate model with the ability to simulate water isotopes has not been evaluated. In this study, we evaluate a novel configuration of the variable-resolution Community Earth System Model that includes stable isotope ratios of water (VR-iCESM) and global ~1° horizontal resolution with regional refinement to 0.125° over the continental United States. VR-iCESM results are compared with observations and an analogous CESM simulation at quasi-uniform 1° resolution to investigate whether VR-iCESM adequately captures observed patterns of precipitation isotopes and if increased horizontal resolution over the continental United States improves data-model agreement over a historical period (1980-2005). Previous studies have shown that VR-CESM is effective at capturing the observed spatial patterns of temperature, precipitation, and snowpack in the Rocky Mountain region. Our preliminary results suggest that VR-iCESM also reasonably captures observed patterns in precipitation isotopes. In addition, increasing horizontal resolution from 1° to 0.125° provides an improvement in simulated patterns of precipitation isotopes in the Rocky Mountain region. This assessment demonstrates that VR-iCESM is capable of capturing fine-scale isotopic processes over mountainous regions, provides a cost-effective alternative to uniform high-resolution climate simulations with water isotope tracers, and shows promise for application to paleoclimate studies.