Response of subtropical stationary waves and hydrological extremes to climate warming in boreal summer

Subtropical stationary waves act as an important bridge connecting regional hydrological extremes with global warming. Observations show that the boreal summer stationary-wave amplitude (SWA) has a significantly positive trend during 1979-2013. Here, we investigate the past and future responses of SWA to increasing climate forcing using 31 CMIP5 GCMs. Twenty-three out of 31 models display a consistent increase in climatological-mean SWA in response to warming. The probability distribution of the normalized SWA trend obtained through bootstrapping shows neither positive nor negative tendencies of SWA trend in pre-industrial control simulations. 22 of 31 models exhibit a positive SWA trend in historical simulations. In RCP8.5 simulations, the SWA trend in 26 of 31 models becomes positive. This finding supports the hypothesis that the positive SWA trend is partially driven by increasing radiative forcing. The regression of hydrological-extreme frequency on SWA suggests that intensified SWA is related to increased heavy-rainfall day frequency over south Asia, the Indochinese Peninsula, east Asia (SA-EA), and to increased dry-spell-day frequency over the central United States, southern United States and Mexico (SUS-MEX). Analysis on changes in spatial pattern of climatological stationary waves from historical to RCP8.5 show the stationary waves is likely to amplify as climate warms. These results provide evidence to explain the intensification of relationship between SWA and hydrological extremes over the regions mentioned above.

Duke Scholars

Author Wenhong Li Earth and Climate Sciences