Double Dynamical Downscaling with WRF for the Western US

Melissa Bukovsky and Changhai LiuNCAR/IMAGe, NCAR/RAL

June 28, 2012

North American Regional Climate Change Assessment Program

• 6 RCMs downscaling 4 AOGCMs (with 12 combinations planned)– Current: 1971-2000 (1999)– Future: 2041-2070 (2069)

• RCMs are also being used to dynamically downscale the NCEP/DOE Reanalysis 2– 1980-2004

• 50-km horizontal resolution over most of North America

• Plus, 2 global 50-km timeslices (GFDL and CAM).

www.narccap.ucar.edu

Doubling Down• Further downscaling of 3 NARCCAP 50-km simulations to 10km

over the West for 10 year periods (+1 year of model spin-up).– 1982-1991– 2046-2055

• Why? To find out if higher-resolution climate information makes a difference in the decision-making of stakeholders.

Naming convention = RCM+driver

• Downscaled WRFG-ncep = WRFH-wncep• Downscaled WRFG-ccsm = WRFH-wccsm

Status• WRFH-wncep = complete• WRFH-wccsm current: just finished• WRFH-wccsm future: 4 years left

Verification Datasets

• UDEL: ½ degree lat/lon resolution (~50 km), monthly average precipitation and temperature

• PRISM: 4 km resolution (regridded to 10 km), monthly average precipitation and temperature

10-km WRF Configuration

• Timestep = 24 - 36s• Radiation = CAM• PBL = YSU• Microphysics = Thompson• Convection = GD• Surface = Noah• + parameter tuning

– LVCOEF = 1– Albedo changes in VEGPARM.TBL– (Also, roughness length over snow modified in SNOWZ0 for

North American domain simulations.)

WRFH-wncep vs. WRFG-ncep

DJF 1982-1991

JJA 1982-1991

DJF 1982-1991

JJA 1982-1991

WRFH-wccsm vs. WRFG-ccsm

DJF 1982-1991

DJF 1982-1991

Discussion

• More analysis to come in the future.• As a modeling study: an interesting way to look

at the propagation of error/bias through different nested simulations.

• As a whole: a necessary step to see if higher-resolution simulations make a difference in impacts related decision making.