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Wednesday, December 23, 2009

M. Sugiyama et al., PNAS 2009, Precipitation extreme changes exceeding moisture content increases in MIROC and IPCC climate models

Proceedings of the National Academy of Sciences,

Precipitation extreme changes exceeding moisture content increases in MIROC and IPCC climate models

Masahiro Sugiyami* (Integrated Research System for Sustainability Science and Transdisciplinary Initiative for Global Sustainability, University of Tokyo, Bunkyo-ku, Tokyo 113-8654, Japan),  Hideo Shiogama (National Institute for Environmental Studies, Tsukuba, Ibaraki 305-8506, Japan) and Seita Emori (National Institute for Environmental Studies, Tsukuba, Ibaraki 305-8506; and Center for Climate System Research, University of Tokyo, Kashiwa-shi, Chiba 277-8568, Japan )

Edited by Kerry A. Emanuel, Massachusetts Institute of Technology, Cambridge, MA, and approved November 24, 2009 (received for review March 23, 2009)


Precipitation extreme changes are often assumed to scale with, or are constrained by, the change in atmospheric moisture content. Studies have generally confirmed the scaling based on moisture content for the midlatitudes but identified deviations for the tropics. In fact half of the twelve selected Intergovernmental Panel on Climate Change (IPCC) models exhibit increases faster than the climatological-mean precipitable water change for high percentiles of tropical daily precipitation, albeit with significant intermodel scatter. Decomposition of the precipitation extreme changes reveals that the variations among models can be attributed primarily to the differences in the upward velocity. Both the amplitude and vertical profile of vertical motion are found to affect precipitation extremes. A recently proposed scaling that incorporates these dynamical effects can capture the basic features of precipitation changes in both the tropics and midlatitudes. In particular, the increases in tropical precipitation extremes significantly exceed the precipitable water change in Model for Interdisciplinary Research on Climate (MIROC), a coupled general circulation model with the highest resolution among IPCC climate models whose precipitation characteristics have been shown to reasonably match those of observations. The expected intensification of tropical disturbances points to the possibility of precipitation extreme increases beyond the moisture content increase as is found in MIROC and some of IPCC models.

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