An Intercomparison of GCM and RCM Dynamical Downscaling for Characterizing the Hydroclimatology of California and Nevada

Abstract

Dynamical downscaling is a widely used technique to properly capture regional surface heterogeneities that shape the local hydroclimatology. However, in the context of dynamical downscaling, the impacts on simulation fidelity have not been comprehensively evaluated across many user-specified factors, including the refinements of model horizontal resolution, large-scale forcing datasets, and dynamical cores. Two global-to-regional downscaling methods are used to assess these: specifically, the variable-resolution Community Earth System Model (VR-CESM) and the Weather Research and Forecasting (WRF) Model with horizontal resolutions of 28, 14, and 7 km. The modeling strategies are assessed by comparing the VR-CESM and WRF simulations with consistent physical parameterizations and grid domains. Two groups of WRF Models are driven by either the NCEP reanalysis dataset (WRF_NCEP) or VR-CESM7 results (WRF_VRCESM) to evaluate the effects of large-scale forcing datasets. The simulated hydroclimatologies are compared with reference datasets for key properties including total precipitation, snow cover, snow water equivalent (SWE), and surface temperature. The large-scale forcing datasets are critical to the WRF simulations of total precipitation but not surface temperature, controlled by the wind field and atmospheric moisture transport at the ocean boundary. No significant benefit is found in the regional average simulated hydroclimatology by increasing horizontal resolution refinement from 28 to 7 km, probably due to the systematic biases from the diagnostic treatment of rainfall and snowfall in the microphysics scheme. The choice of dynamical core has little impact on total precipitation but significantly determines simulated surface temperature, which is affected by the snow-albedo feedback in winter and soil moisture estimations in summer.

The Changing Character of the California Sierra Nevada as a Natural Reservoir

“…Although the NA‐CORDEX ensemble only provides simulation data at 25‐ and 50‐km resolutions, coarser than generally preferred for mountain snowpack products (Ikeda et al, ; Letcher & Minder, ; Pavelsky et al, ; Wrzesien et al, ; Wrzesien et al, ), it is nonetheless a significant improvement over other multimodel ensembles such as the Coupled Model Intercomparison Project phase 5 (CMIP5) GCM ensemble. Further, it is at a sufficiently high resolution to still provide value for snowpack assessment when factoring in the important trade‐offs between model resolution, subgrid‐scale parameterizations, and global forcing data set (Rhoades, Ullrich, Zarzycki, et al, ; Xu et al, ).…”

Evaluating Variable‐Resolution CESM Over China and Western United States for Use in Water‐Energy Nexus and Impacts Modeling

“…Of particular interest to this study, VR‐CESM has demonstrated good performance in modeling the regional hydroclimate over the western United States. (Huang & Ullrich, 2016, 2017; Huang et al., 2016; Rhoades, Ullrich, et al., 2018; Rhoades et al., 2016, 2017; Wang & Ullrich, 2018; Wang et al., 2018b; C. Wu et al., 2017; Xu et al., 2018), the eastern U.S. (Burakowski et al., 2019; Zarzycki, 2018; Zarzycki et al., 2014, 2015, 2016) and, more recently, Greenland (van Kampenhout et al., 2019) and the Tibetan Plateau (Rahimi et al., 2019) when compared with fine‐resolution regional climate models (RCMs), reanalyses, and reference data sets across daily, seasonal, and decadal time scales. In addition to VR‐CESM, a few other variable‐resolution GCMs are available including the Energy Exascale Earth System Model (E3SM) (Tang et al., 2019), Geophysical Fluid Dynamics Laboratory finite‐volume dynamical core on the cubed sphere (FV3) (Harris & Lin, 2013, 2014; Hazelton et al., 2018), and the Model for Prediction Across Scales (MPAS) (Hagos et al., 2013, 2018; Heinzeller et al., 2016).…”

The Shifting Scales of Western U.S. Landfalling Atmospheric Rivers Under Climate Change

“…Yet, global climate models are one of the only ways in which to assess the nonlinear effects of climate change on AR behavior, particularly the interplay between dynamical and thermodynamical responses to climate change and their influences on IVT (Payne et al, 2020). Variable‐resolution global climate modeling techniques are a means to bridge this global‐to‐regional scale mismatch and have been used extensively to investigate various aspects of western U.S. hydroclimate (Gettelman et al, 2018; Goldenson et al, 2018; Huang et al, 2016; Rhoades et al, 2016; Rhoades, Ullrich, & Zarzycki, 2018; Rhoades, Ullrich, et al, 2018; Rhoades et al, 2020; Wu et al, 2017; Wang & Ullrich, 2018; Xu et al, 2018).…”