Exploring a Variable-Resolution Approach for Simulating Regional Climate Over the Tibetan Plateau Using VR-CESM

This study implements a variable resolution version of Community Earth Systems Model (VR-CESM; regionally refined at 1/8 degrees resolution) to assess the improvement in simulating the seasonal climate across the Tibetan Plateau (TP) at higher horizontal resolutions compared to its uniform (UN) 1 degrees counterpart (UN-CESM). The Weather Research and Forecasting (WRF) model, run at 12-km horizontal grid spacing, is compared to both CESM simulations. VR-CESM and WRF are more comparable to satellite and surface-based observations than UN-CESM in simulating summertime (June to August) temperature across the TP and TP foothills, respectively. WRF and VR-CESM also more accurately simulate precipitation than UN-CESM across the region due to more accurate terrain treatment. The number of days in which effective (> 2.5 mm/day) and heavy (> 25 mm/day) precipitation events are generally better captured in VR-CESM compared to UN-CESM and WRF. Finally, snow cover fraction in VR-CESM is better simulated for all months compared to UN-CESM, with the largest improvements simulated from June to August, while WRF performs even better than VR-CESM in simulating snow cover fraction. The improvements in simulated temperature, precipitation, and snow cover are due to WRF and VR-CESM's ability to resolve more complex topographic features rather than time step differences between the UN-CESM and VR-CESM experiments. While it is fairly intuitive that improved topography accuracy should bring forth more accurate simulated meteorology, this evaluation suggests that VR-CESM is competitive or may even be preferred over regional climate models (such as WRF) when examining internal and external climate variability, as it bypasses several drawbacks associated with regional climate models.