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

Jian Lu,Gang Chen,P Staten,Yang Gao,L R Leung,Daokai Xue

doi:10.1038/s41612-018-0017-9

Abstract

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 widetilde {(P - E)}^ + 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.

Highlights

The winter of 2016/2017 marked one of the wettest winters for the western United States, with Nevada and California witnessing their wettest and second wettest winter ever on record, respectively
The zonal mean column integrated water vapor (CWV) wave activity can be manifested in the regional hydrological features like atmospheric rivers (ARs), the moisture transport function of which and the associated large hydrological cycling rate (HCR) upon making landfall are revealed by the local CWV wave activity analysis
An important distinction here is that the background CWV gradient is enhanced under warming for the latitudinal range examined, while the opposite is true for the surface temperature gradient associated with polar amplification

Summary

Introduction

The winter of 2016/2017 marked one of the wettest winters for the western United States, with Nevada and California witnessing their wettest and second wettest winter ever on record, respectively. The western US experiences large interannual and interdecadal variability associated with climate modes such as El Niño-Southern Oscillation and Pacific Decadal Oscillation, the record-setting hydrological events could have an anthropogenic contribution as the atmospheric moisture holding capacity increases in a warmer climate, amplifying both the wet and dry extremes.[1] Many studies[2,3,4,5,6] have documented that future warming would lead to enhanced moisture transport by the atmospheric rivers (ARs), synoptic scale features responsible for concentrated supply of moisture from the tropics to the western US,[7,8] causing more frequent and more intense precipitation extremes. There is a critical need for a more rigorous diagnostic framework for the hydrological extremes, preferably with dynamical underpinnings

Methods

Results

Conclusion