Impact of Climate Change on Winter Storm Moisture Transport over the Western United States

The Pacific Northwest frequently experiences extreme precipitation from atmospheric river events. Atmospheric rivers (ARs) are long filamentary bands of moisture that originate in the tropics or subtropics and extend into the midlatitudes. ARs can transport large amounts of moisture, causing heavy orographic precipitation. In November 2006, Glacier National Park received enough heavy precipitation from an AR to cause severe flooding, despite its inland location. Climate change is likely to have an impact on winter storms, particularly the moisture transport of ARs. Warmer environments can both carry more moisture and enhance storm intensity, potentially increasing precipitation and its impacts. 

The Weather Research and Forecasting (WRF) model was used to simulate the 2006 AR case study, using 4-km horizontal grid spacing and Climate Forecast System Reanalysis initial and lateral boundary conditions (i.e., the “control run”). Experimental simulations were also generated for the same event using the “pseudo global warming” (PGW) method, which obtains differences in long-term averages from one or more climate models. The differences between the years 2071-2080 and 1990-2005 were obtained from the National Center for Atmospheric Research Community Earth System Model Large Ensemble. These differences between temperature and moisture are used to modify WRF boundary and initial conditions to simulate future scenarios. Differences between the control and PGW runs are used to understand how changing thermodynamic and other dynamic processes influence moisture transport.  The results indicate how increasing temperature and moisture associated with climate change impact moisture flux, precipitation, and other storm-related processes over complex western US terrain.