587 Dynamical Downscaling Projections of Late 21st Century Atlantic Hurricane Activity: CMIP3 and CMIP5 Model-based Scenarios

Thursday, 10 January 2013
Exhibit Hall 3 (Austin Convention Center)
Thomas R. Knutson, NOAA/GFDL, Princeton, NJ; and J. J. Sirutis, G. A. Vecchi, S. Garner, M. Zhao, H. S. Kim, M. Bender, I. Held, R. E. Tuleya, and G. Villarini

Handout (4.6 MB)

The robustness of late 21st century dynamical model projections of intense Atlantic hurricane activity is examined. Multi-model ensemble climate change scenarios from CMIP3/A1B and CMIP5/RCP4.5 are compared. Ten individual CMIP3 models are downscaled. Dynamical downscalings are compared from a 18 km grid regional model and a 50 km grid global model. To simulate intense hurricanes, each storm from the regional model is downscaled using the GFDL hurricane model, which has grid spacing as fine as 9 km and ocean coupling. A significant (p=0.05) reduction in the frequency of tropical storms and hurricanes is projected for both CMIP3 (-23%) and CMIP5 (-27%) ensembles, and by five of ten individual CMIP3 models that were downscaled. However, for strong category 4+ hurricanes (winds of at least 65 m s-1), we find a significantly increased frequency for the CMIP3 ensemble (+250%); for the CMIP5 ensemble we find a smaller (nonsignificant) increase (+84%). For the frequency of Category 4-5 hurricanes (winds >= 59 m s-1) the Bender et al. (2008) CMIP3-based study had projected a significant increase (+87%); the CMIP5 ensemble projects a smaller (non-significant) increase (+39%). Three of ten individual CMIP3 models show a significant increase in frequency of both Category 4-5 hurricanes and hurricanes stronger than 65 m s-1. Tropical cyclone-related rainfall rates, averaged within 100 km of the storm, increase significantly by 23% (CMIP3) and 14% (CMIP5). The fractional increase in precipitation approximates that expected from water vapor content scaling considerations for relatively large radii (200-400 km), but is substantially higher at relatively smaller radii (50-150 km).
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