07 June 2014

The Robust Dynamical Contribution to Precipitation Extremes in Idealized Warming Simulations across Model Resolutions


Precipitation extremes are a topic of intensive study because of their disproportionally large socioeconomic impacts. While the intensification of precipitation extremes under climate warming has been mostly attributed to the increased water vapor-holding capacity, how atmospheric dynamical changes may have an imprint on precipitation extremes remains unclear. To better understand these factors, research led by DOE scientists at Pacific Northwest National Laboratory studied the precipitation extremes in a suite of aqua-planet, Community Atmospheric Model Version 3 simulations with various horizontal resolutions. Using two approaches, PDF-based and percentile-based, the team found both approaches point consistently to a notion that the dynamical shift in circulation contributes substantially to the response of precipitation extremes (in terms of both intensity and frequency). However, the thermodynamic contribution is less than what the Clausius-Clapeyron relation would suggest, and thus appears to contradict earlier studies that attributed the increase of the extra-tropical precipitation extremes mostly to thermodynamic causes. Coarser resolutions underestimate not only the intensity of the precipitation extremes, but also the dynamical contribution to the increase of precipitation extremes. This study offers a fresh perspective for interpreting the change of precipitation extremes under global warming forcing, and provides understanding for the manifold increase in the frequency of the most extreme categories of the precipitation events at the poleward side of the mid-latitude storm track.