Downscaling hydroclimatic changes over the Western U.S. Based on CAM subgrid scheme and WRF regional climate simulations

Journal Article · Tue Apr 28 00:00:00 EDT 2009 · International Journal of Climatology

DOI:https://doi.org/10.1002/joc.1928· OSTI ID:1719126

Qian, Yun  ^[1]; Ghan, Steven J.  ^[1]; Leung, Lai-Yung  ^[1]

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1. BATTELLE (PACIFIC NW LAB)

Global and regional climate simulations have been performed to compare two dynamical downscaling methods, a regional climate model (WRF) and a subgrid parameterization, both driven by a global climate model, for simulating orographic effects and projecting the hydrologic impacts of climate change in the western U.S. Two 10-year simulations were completed for the present (1993-2003) and future (2039-2049) with CAM3 applied a subgrid orographic precipitation scheme and with WRF regional climate model at 15 km spatial resolution Increasing spatial resolution has a large impact on snowpack simulation. Both CAM subgrid scheme and the WRF simulation significantly improved the simulation of snowpck associated with orographic effects. The spatial distributions of the precipitation and snowpack are generally consistent between the CAM Subgrid scheme and WRF simulations, as CAM3 provided the large-scale circulation for both simulations. However, rain-shadow and snowpack-shadow effects are only resolved at the explicit grid resolution. Both downscaling procedures preserved the CAM large-scale features, showing an increase in precipitation in southern states in WUS and a significant decrease in the Pacific Northwest. The WRF simulation indicates larger changes of precipitation and snowpack along the coastal mountains than CAM3. As the WRF model explicitly simulates the interactions of regional atmospheric circulation and the underlying topography, changes in the future climate may lead to larger changes in orographic precipitation than that caused by changes in atmospheric moisture and temperature alone. The surface air temperature increase 0.5-2.0 oC over most of areas with maximum warming in Rockies and northern areas of model domain. Snowpack reduces 20-60% with maximum reductions along the Cascades and the Rockies. Runoff changes show a diverse spatial pattern in different seasons driven by the combined impacts from the changes of precipitation, more precipitation in the form of rain rather than in snow, and less snowpack accumulation in warmer winter.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1719126
• Report Number(s): PNWD-SA-8304
• Journal Information: International Journal of Climatology, Vol. 30, Issue 5
• Country of Publication: United States
• Language: English