5 Sensitivities of Extreme Precipitation to Global Warming Are Lower over Mountains than over Oceans and Plains

Monday, 27 June 2016
Green Mountain Ballroom (Hilton Burlington )
Xiaoming Shi, University of California, Berkeley, CA; and D. R. Durran

Climate-model simulations predict an intensification of extreme precipitation in almost all areas of the world under global warming. Local variations in the magnitude of this intensification are evident in these simulations, but most previous efforts to understand the factors responsible for the changes in extreme precipitation focused on zonal averages and neglected zonal variations, leading to uncertainties in the understanding and estimation of regional responses. Here the spatial heterogeneity of the warming-induced response of extreme precipitation is studied in climate-model simulations with idealized orography and land-sea distributions. It is shown that the sensitivity of extreme precipitation to warming (its fractional rate of increase in intensity with global-mean surface temperature) is about 3% per K lower over the mountains than over the oceans and the plains.

Dividing the fundamental factors regulating the changes in precipitation intensity between thermodynamic and dynamic effects, this difference in sensitivity may be linked to differences in the dynamics governing the response of the vertical velocity field. In these extreme events, mountain-wave dynamics control the moist ascent over the terrain, while mid-latitude cyclone dynamics govern moist ascent over the oceans and plains. The response over mountains is mainly controlled by changes in upper-level dry static stability and horizontal winds. The response over the plains and oceans is linked to the decreases in the ratio of the moist static stability in the saturated core of intense extra-tropical cyclones to the dry stability in surrounding regions, which both intensifies the ascent and reduces the horizontal extent of the region of the rising air.

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