Enhanced hydrological extremes in the western United States under global warming through the lens of water vapor wave activity

A novel diagnostic framework based on the wave activity of column integrated water vapor (CWV) is used to probe into the higher moments of the hydrological cycle with bearings on the extremes. Applying the CWV wave activity analysis to the historical and RCP8.5 scenario simulations by the CMIP5 models reveals a super Clausius–Clapeyron rate of increase in the wet vs. dry disparity of daily net precipitation due to the enhanced stirring length of wave activity at the poleward flank of the storm track, despite a decrease in the hydrological cycling rate (HCR) measured by the reciprocal of wave activity residence time. The local variant of CWV wave activity unravels the unique characteristics of atmospheric rivers (ARs) in terms of their transport function and locally enhanced mixing efficiency. Under RCP8.5, the local moist wave activity increases by ~40% over the northeastern Pacific and western United States by the end of the 21st century, indicating lengthening and more frequent landfalling ARs with a consequence of a ~20% increase in the related hydrological extremes (−)$^+$ in the west coast, despite a robust weakening of the local HCR. These results imply that the unusually wet winter the west coast just experienced in 2016/17 might be a harbinger of more frequent wet extremes in a warmer climate