Projected Changes in Heavy Precipitation over North America in CMIP5 Climate Model Simulations

Coupled atmosphere-ocean climate models from the Coupled Model Intercomparison Project Phase V (CMIP5) are used to study projected changes in heavy to extreme daily precipitation over North America between the late 20th century and late 21st century under the RCP8.5 emissions scenario. Preliminary results show that heavy precipitation increases over much of North America between the late 20th and 21st centuries, with generally larger increases at higher latitudes and near the Atlantic and Pacific coasts. During summer, increases in heavy precipitation are confined to very high latitudes, while only small changes in heavy precipitation occur elsewhere. Heavy precipitation decreases in intensity and frequency over some low latitude regions during certain seasons, such as western Mexico and the adjacent Pacific Ocean during winter and spring. The increases in heavy precipitation found here are consistent with previous studies, which found increases in observed heavy and extreme precipitation over the 20th century and well as increases in simulated extreme precipitation in response to greenhouse warming over much of North America. We also investigate local and regional changes in the distribution of daily precipitation events and the intermodel variability of such changes in the CMIP5 simulations. Finally, we investigate the quantitative relationship between projected changes in extreme precipitation and surface warming to see if projected increases in extreme precipitation are governed by atmospheric water vapor constraints. A composite analysis of various physical quantities describing the atmospheric dynamic and thermodynamic structure associated with extreme precipitation events is also used to see if changes in the large scale atmospheric circulation are associated with changes in extreme precipitation at specific locations.