Exploring a Variable‐Resolution Approach for Simulating Regional Climate in the Rocky Mountain Region Using the VR‐CESM

Abstract

The reliability of climate simulations and projections, particularly in the regions with complex terrains, is greatly limited by the model resolution. In this study we evaluate the variable‐resolution Community Earth System Model (VR‐CESM) with a high‐resolution (0.125°) refinement over the Rocky Mountain region. The VR‐CESM results are compared with observations, as well as CESM simulation at a quasi‐uniform 1° resolution (UNIF) and Canadian Regional Climate Model version 5 (CRCM5) simulation at a 0.11° resolution. We find that VR‐CESM is effective at capturing the observed spatial patterns of temperature, precipitation, and snowpack in the Rocky Mountains with the performance comparable to CRCM5, while UNIF is unable to do so. VR‐CESM and CRCM5 simulate better the seasonal variations of precipitation than UNIF, although VR‐CESM still overestimates winter precipitation whereas CRCM5 and UNIF underestimate it. All simulations distribute more winter precipitation along the windward (west) flanks of mountain ridges with the greatest overestimation in VR‐CESM. VR‐CESM simulates much greater snow water equivalent peaks than CRCM5 and UNIF, although the peaks are still 10–40% less than observations. Moreover, the frequency of heavy precipitation events (daily precipitation ≥ 25 mm) in VR‐CESM and CRCM5 is comparable to observations, whereas the same events in UNIF are an order of magnitude less frequent. In addition, VR‐CESM captures the observed occurrence frequency and seasonal variation of rain‐on‐snow days and performs better than UNIF and CRCM5. These results demonstrate the VR‐CESM's capability in regional climate modeling over the mountainous regions and its promising applications for climate change studies.

Impacts of absorbing aerosol deposition on snowpack and hydrologic cycle in the Rocky Mountain region based on variable-resolution CESM (VR-CESM) simulations

“…Compared to United States Geological Survey (USGS) 3 km topography data , the topography data used in VR-CESM resolve the variations in terrain in the Rocky Mountains well (see Fig. 2 of Wu et al, 2017). In Wu et al (2017), we have shown that VR-CESM performs well in the simulation of regional climate patterns, including spatial distributions and the seasonal evolution of temperature, precipitation, and snowpack in the Rocky Mountain region.…”

“…The variable-resolution grid is the same as that used in Wu et al (2017) and is generated by the open-source software package called SQuadGen (Ullrich, 2014). A topographical dataset for this variable-resolution grid is also generated accordingly by the National Center for Atmospheric Research (NCAR) global model topography generation software called NCAR_Topo (v1.0) (Lauritzen et al, 2015) as described in Wu et al (2017). Figure 1b shows the spatial variations in terrain height for the variable-resolution grid used in VR-CESM.…”

“…The model has also been used in the regional climate simulations over the western US, and the results show that the VR-CESM is capable of reproducing the spatial patterns and the seasonal evolution of temperature, precipitation, and snowpack in the Sierra Nevada Rhoades et al, 2016) and Rocky Mountains (Wu et al, 2017). In particular, VR-CESM reasonably simulates the magnitude of snow water equivalent, the timing of snow water equivalent peaks, and the duration of snow cover in the Rocky Mountains, as shown in comparison with Snow Telemetry (SNOTEL) and MODIS (Moderate Resolution Imaging Spectroradiometer) snow cover observations (Wu et al, 2017).…”

“…Both snowfall and snow accumulation depend on temperature and precipitation, and thus the distribution of snowpack depends strongly on topographic variability. Current GCMs with a typical horizontal resolution of 1 to 2 • cannot resolve the snowpack over regions with complex terrains (e.g., Rocky Mountains) due to the coarse resolution Wu et al, 2017), which impedes the reliable quantification of SDE by LAAs in mountainous regions (e.g., Flanner et al, 2007;Yasunari et al, 2015). RCMs can simulate the snowpack more accurately than coarse-resolution GCMs, but they are not able to simulate the global transport of aerosols to the focused region except when aerosol transport along the boundary is prescribed (e.g., Qian et al, 2009).…”

“…Following the evaluation study of Wu et al (2017), here we use VR-CESM to investigate the impacts of LAAs in snow (BC and dust) on the snowpack and hydrologic cy- cles over the Rocky Mountains. By comparing the two VR-CESM simulations with and without LAAs in snow, we examine the impacts on surface radiative transfer, temperature, snowpack, and runoff induced by LAAs in snow.…”