Global Projections of Intense Tropical Cyclone Activity for the Late 21st Century from Dynamical Downscaling of CMIP5/RCP4.5 Scenarios

Global projections of intense tropical cyclone activity are derived from the GFDL HiRAM (50 km grid) atmospheric model and the GFDL hurricane model using a two-stage downscaling procedure. First, tropical cyclone genesis is simulated globally using the 50 km grid atmospheric model. Then each of these storms is downscaled into the GFDL hurricane model, which has horizontal grid-spacing near the storm of 6 km, and includes interactive ocean coupling (i.e., ‘cold wake' generation). Simulations are done for observed SSTs (1980-2008); for a “control run” with repeating seasonal cycle; and for a late 21st century projection using an altered seasonal cycle of SSTs according to a CMIP5/RCP4.5 multi-model ensemble. In general agreement with most previous studies, the climate change projections with this framework indicate fewer tropical cyclones globally in a warmer late-21st-century climate, but also indicate an increase in their average intensity, precipitation rates, and in the number and occurrence-days of very intense category 4-5 storms. While these changes are apparent in the globally averaged tropical cyclone statistics, they are not necessarily present in each individual basin.