“If it happened in…” a pseudo-global warming assessment of tropical cyclone tornadoes
The overarching goal of this dissertation is to investigate the impacts of anthropogenic climate change on the production of tornadoes by tropical cyclones (TCs) making landfall in the United States Atlantic Basin. Hurricane Ivan (2004), a prolific tropical cyclone tornado (TCT)-producing storm, is the particular case under consideration. This dissertation also seeks to document changes in risk due to these changes in the tornado production in future climates. The work under this dissertation is associated with three objectives. The first objective is to verify the ability of the Weather Research and Forecasting (WRF) model to simulate Hurricane Ivan, and its TCT production, under its current-climate forcings. The simulated TC track and intensity matched well with observations post landfall, and the simulated TC structure closely replicated the observed structure in terms of its shape and primary rainbands. TC tornado surrogates (TCTSs) were identified and calibrated using thresholds based on percentile values of maximum updraft helicity (UHmax) and simulated radar reflectivity. Although the magnitude of UHmax generally decreased as the simulated TC moved inland, sensitivity testing revealed that a threshold based on the 99.95% percentile value of UHmax achieved optimal TCTS coverage and agreement with observed TCT tracks on WRF domains with 3-km and 1-km grid spacings. Three cells were identified at three different stages of the TC inland evolution and were found to have hook appendages resembling supercells found in non-tropical environments. The cells produced storm tops of 13 km, with rotating cores with depths of 4 to 6 km. Doppler-radar-derived rotation tracks, which have been found to be useful to identify and track mesocyclones in Great Plains supercells, were evaluated for possible applicability to TC spawned tornadoes. The second objective is to determine changes in surrogate TCT generation in future environments under climate change. This is done by comparing the control simulation (CTRL) to simulations conducted using a “pseudo-global” warming (PGW) approach, which allows for an assessment of impacts of climate changes on specific weather and climate events. The PGW simulations involve future climate conditions over the late (2080-2090) 21st century period under RCP 8.5, using the Community Climate System Model version 4 (CCSM4), Model for Interdisciplinary Research on Climate version 5 (MIROC5), and Geophysical Fluid Dynamics Laboratory Climate Model version 3 (CM3). Changes in TC intensity and TCT production for the PGW-modified Ivan are documented and analyzed. Compared to the CTRL, all three PGW simulations show an increase in TC intensity, as well as westward shifting tracks. The most significant changes are found in the accumulated rainfall over the course of Ivan’s progression overland. Regarding TCT production, MIROC produced more TCTSs than the CTRL overall, while the CM3 and CCSM4 models produced fewer TCTSs. An assessment of pre-landfall TCTSs shows that all three PGW TCs were more intense, and produced more TCTSs, than did the CTRL. The final objective seeks to understand how disaster risk might change under different hazard scenarios of a historical TCT-producing event modified by climate change, and simultaneously under projected changes in the exposed population. This study shows that Hurricane Ivan in a future climate results in a greater event-specific disaster risk, due in part to the increase in hazard from TCTSs, occurring in regions with vulnerable populations. The increase in risk for the future population is due to the shift in larger populations into more socially vulnerable areas.
Tropical cyclone tornadoes, TCT, societal impact of hurricanes, pseudo-global warming, PGW, PGW and hurricanes, high resolution modeling of tropical cyclone tornaodoes
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign