Synthesis of Inland Impacts of Atlantic Tropical Cyclones

Tropical cyclones (TCs) are an important and widely recognized phenomenon known for being costly and deadly. Much research has focused on how climate change may affect TCs, specifically on changes in TC intensity and frequency over the ocean, with significantly less research into post-landfall TC changes. The increase in sea surface and air temperature will affect not only TCs over the ocean but also over land, with some research suggesting prolonged inland TC intensity after landfall (e.g., Li and Chakraborty 2020). Studies have shown that as a result of climate change, there may be an increase in the intensity of TCs, a possible slowdown of TC translation speed, increased rainfall, and changes in the structure (Hill and Lackmann 2009, Kossin 2018, Knutson, et al. 2020). Some of these changes can affect the inland extension of extreme weather conditions, such as damaging wind, heavy rainfall, and bivariate hazards. Using a diverse set of storms, all run as an ensemble, we evaluated how inland wind decay and spatial impacts may change in a warmer climate.

Building on previous research and using the Weather Research and Forecasting (WRF) model, we simulated North Atlantic Hurricanes Fran (1996), Floyd (1999), Frances (2004), Ivan (2004), Matthew (2016), and Florence (2018), in a present and future climate. These storms, all of which affected the southeastern U.S., each were associated with unique impacts, including heavy rain, flooding, high winds, and landslides. For each storm, we ran an ensemble of simulations, varying microphysics, and planetary boundary layer schemes. With the use of a pseudo-global warming approach, we applied the RCP8.5 scenario from CMIP5 or SSP5-8.5 from CMIP6 to warm SST, soil, skin, and atmospheric temperatures to end-of-century levels while allowing relative humidity to remain constant. Doing this implies an increase in the water vapor content to maintain the same relative humidity. These experiments provided a more equal comparison between present-day and future simulations of this storm. We found that future Atlantic TCs have a greater extent of tropical storm-force winds and bivariate (rain and wind) impacts, despite the 10-m maximum wind speed decaying faster. A smaller radius of maximum in future simulations also corresponded to increased decay rates but structurally, PV and tangential velocity, the storms were more intense.

References:

Hill, Kevin A., and Gary M. Lackmann. "Influence of environmental humidity on tropical cyclone size." Monthly Weather Review 137.10 (2009): 3294-3315.

Knutson, T., et al., 2020: Tropical cyclones and climate change assessment: Part II: Projected response to anthropogenic warming. Bull. Amer. Met. Soc. 101: 303-322.

Kossin, J. P., 2018: A global slowdown of tropical-cyclone translation speed. Nature 558.7708: 104-107.

Li, L., and P. Chakraborty, 2020: Slower decay of landfalling hurricanes in a warming world. Nature 587.7833, 230-234.