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

Abstract

Global projections of intense tropical cyclone activity are derived from the Geophysical Fluid Dynamics Laboratory (GFDL) High Resolution Atmospheric Model (HiRAM; 50-km grid) and the GFDL hurricane model using a two-stage downscaling procedure. First, tropical cyclone genesis is simulated globally using HiRAM. Each storm is then downscaled into the GFDL hurricane model, with horizontal grid spacing near the storm of 6 km, including ocean coupling (e.g., “cold wake” generation). Simulations are performed using observed sea surface temperatures (SSTs) (1980–2008) for a “control run” with 20 repeating seasonal cycles and for a late-twenty-first-century projection using an altered SST seasonal cycle obtained from a phase 5 of CMIP (CMIP5)/representative concentration pathway 4.5 (RCP4.5) multimodel ensemble. In general agreement with most previous studies, projections with this framework indicate fewer tropical cyclones globally in a warmer late-twenty-first-century climate, but also an increase in average cyclone intensity, precipitation rates, and the number and occurrence days of very intense category 4 and 5 storms. While these changes are apparent in the globally averaged tropical cyclone statistics, they are not necessarily present in each individual basin. The interbasin variation of changes in most of the tropical cyclone metrics examined is directly correlated to the variation in magnitude of SST increases between the basins. Finally, the framework is shown to be capable of reproducing both the observed global distribution of outer storm size—albeit with a slight high bias—and its interbasin variability. Projected median size is found to remain nearly constant globally, with increases in most basins offset by decreases in the northwest Pacific.

Dynamical downscaling of tropical cyclones from CCSM4 simulations of the Last Glacial Maximum

“…For regional TC climate simulation, domain size and grid spacing play important roles [Vannitsem and Chome, 2005;Kumar et al, 2011;Done et al, 2015]. In particular, high spatial resolution is needed to simulate the full spectrum of observed TC intensities up to Category 5 in the Saffir-Simpson scale, and model grid spacing should be as small as in operational forecasting models ($4 km) [Bender et al, 2010;Done et al, 2015;Knutson et al, 2015]. Only recently, global climate models with a horizontal grid with resolution above $18 km started to be able to simulate major hurricanes (Categories 3-5) with maximum winds greater than 50 m s 21 , but even those that cannot simulate the most intense storms have been useful to study other aspects of the TC climatology such as their frequency, genesis, and intensity changes in weaker systems [Knutson et al, 2008].…”

“…Emanuel [2005] and Webster et al [2005] related increases in intense storms to concurrent increases in sea surface temperatures, but questions regarding the accuracy and completeness of the historical TC record persist [e.g., Landsea et al, 2006;Klotzbach and Landsea, 2015], and reliable global data are limited only to the recent decades of the satellite era. Efforts to understand how storms may respond to projections of climate changes over the next century have largely focused on analysis of model simulations; these include analysis of large-scale environmental factors known to favor genesis and intensification [e.g., Camargo et al, 2007aCamargo et al, , 2007bCamargo et al, , 2014, analysis of explicitly resolved storms simulated directly in global climate models [e.g., Camargo, 2013;Camargo and Wing, 2016], and several downscaling techniques to simulate storms in higher-resolution models better suited to resolving storm structure and intensity [e.g., Emanuel, 2013;Knutson et al, 2015].…”

“…These projections are obtained using high-resolution global climate models [e.g., Murakami et al, 2012;Zhao and Held, 2012], high-resolution idealized experiments [Rappin et al, 2010;Merlis et al, 2016], as well as using dynamical downscaling using regional climate models [Knutson et al, 2008;Bender et al, 2010]. For instance, Knutson et al [2015] considered storms produced by a global model, but then used a higher-resolution model in order to simulate the most intense storms. The increase in the occurrence of the most intense storms under global warming is consistent with increases in potential intensity [e.g., Emanuel, 1987], while the decrease in the number of storms simulated with warming may be sensitive to the survival of weak systems [e.g., Emanuel et al, 2010].…”

Hurricane Sandy’s flood frequency increasing from year 1800 to 2100

“…We estimate the current and future hurricane surge climatology for NYC following ref. 9, using large numbers of synthetic surge events that are generated with a statistical deterministic hurricane model (10) and a high-resolution hydrodynamic model (11 (12) and initial numerical evidence that storm size may change little on average over the 21st century climate (14). By comparing the NCEP estimates and GCM estimates for the same period of 1981-2000, ref.…”

Natural hazards in Australia: storms, wind and hail

“…For the design 84 and assessment of buildings and structures, the region of influence of TCs is deemed to be coastal boundaries may need to be extended further south (Holmes 2008(Holmes , 2011Kossin et al 2014) 88…”