The physical basis for increases in precipitation extremes in simulations of 21st-century climate change
Global warming is expected to lead to a large increase in atmospheric water vapor content and to changes in the hydrological cycle, which include an intensification of precipitation extremes. The intensity of precipitation extremes is widely held to increase proportionately to the increase in atmospheric water vapor content. Here, we show that this is not the case in 21st-century climate change scenarios simulated with climate models. In the tropics, precipitation extremes are not simulated reliably and do not change consistently among climate models; in the extratropics, they consistently increase more slowly than atmospheric water vapor content. We give a physical basis for how precipitation extremes change with climate and show that their changes depend on changes in the moist-adiabatic temperature lapse rate, in the upward velocity, and in the temperature when precipitation extremes occur. For the tropics, the theory suggests that improving the simulation of upward velocities in climate models is essential for improving predictions of precipitation extremes; for the extratropics, agreement with theory and the consistency among climate models increase confidence in the robustness of predictions of precipitation extremes under climate change.
Copyright ©2009 by the National Academy of Sciences. Communicated by Kerry A. Emanuel, Massachusetts Institute of Technology, Cambridge, MA, July 14, 2009 (received for review March 24, 2009). Published online before print August 19, 2009, doi: 10.1073/pnas.0907610106 We thank the modeling groups, the Program for Climate Model Diagnosis and Intercomparison and the World Climate Research Programme's Working Group on Coupled Modelling for their roles in making available the World Climate Research Program Coupled Model Intercomparison Project phase 3 multimodel dataset. Support of this dataset was provided by the Office of Science, U.S. Department of Energy. This work was supported by David and Lucile Packard Fellowship and by the National Science Foundation Grant ATM-0450059. The Global Precipitation Climatology Project 1-degree daily precipitation dataset was downloaded from http://www1.ncdc.noaa.gov. National Centers for Environmental Prediction-Department of Energy Reanalysis 2 data were provided by the National Oceanic and Atmospheric Administration/Office of Oceanic and Atmospheric Research/Earth System Research Laboratory Physical Sciences Division at www.cdc.noaa.gov. Author contributions: P.A.O. and T.S. designed research; P.A.O. and T.S. performed research; P.A.O. analyzed data; and P.A.O. and T.S. wrote the paper. The authors declare no conflict of interest. This article contains supporting information online at www.pnas.org/cgi/content/full/0907610106/DCSupplemental.
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Supplemental Material - 0907610106SI.pdf