15 February 2016

Scientists Project Large Increase in Extreme Precipitation over Western North America Due to Global Warming


Precipitation from atmospheric rivers (ARs) supply water and can also cause flooding. Understanding how ARs respond to climate change will be important to climate adaptation planning by communities needing to prepare for extreme weather. Department of Energy scientists at Pacific Northwest National Laboratory (PNNL) analyzed 180-year-long simulations from the Community Earth System Model (CESM) Large Ensemble project to see how ARs respond to climate change. After accounting for the effects of model bias, the model projects an ensemble mean increase of 35% in the number of landfalling AR days between the last twenty years of the 20th and 21st centuries under RCP8.5 scenario. In the same time period, the model projects a 28% increase in extreme precipitation days. This projected increase is less than the increase in AR days because despite an increase in water vapor in a warmer climate, the moisture transport needed to produce extreme precipitation also increases due to increased atmospheric stability with warming.The increases in AR days and extreme precipitation days are much larger than the uncertainties associated with model bias (1%) and natural variability (7%). These robust changes have important implications for climate resiliency. Future assessment of sub-regional changes of AR and extreme precipitation can adopt a similar approach to bias-correct the model-projected changes.

Samson M. Hagos

This research is based on work supported by the U.S. Department of Energy Office of Science Biological and Environmental Research as part of the Regional and Global Climate Modeling Program. The CESM project is supported by the National Science Foundation and the Office of Science (BER) of the U.S. Department of Energy. Computing resources for the model simulations are provided by the National Energy Research Scientific Computing Center (NERSC). Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy under contract DE-AC05-76RLO1830.