Anthropogenic Influences on the Intensity and Rainfall of Major Tropical Cyclone Events

There is no consensus on whether anthropogenic climate change has yet impacted tropical cyclones (TCs), in part because natural variability is large and consistent TC observations cover less than a century. Furthermore, projections of future TC activity are uncertain, as they often rely on climate models that parameterize convection and have difficulty representing intense TCs. Here we advance our understanding of anthropogenic influences on TCs by 1) quantifying the uncertainty in the response of TCs to anthropogenic forcings due to convective parameterization and 2) investigating how recent destructive TCs would change if similar events occurred in worlds with reduced or increased greenhouse gas concentrations. We performed a 10-member ensemble of regional climate model hindcasts of Hurricane Katrina (2005) at 3 km, 9 km, and 27 km resolution. In addition, simulations representing Katrina in a world without human influences and under a high greenhouse gas emissions scenario were conducted by adjusting the prescribed sea-surface temperature, lateral boundary conditions, and greenhouse gas concentrations. We found that although climate change to date did not significantly influence Katrina’s simulated intensity, it did enhance rainfall. Experiments with and without parameterized convection suggest that convective parameterization introduces minimal uncertainty into the sign of projected TC intensity changes. We then examined how 13 highly impactful TC events in the Atlantic, Eastern and Western North Pacific, South Pacific, and Southwestern Indian Oceans would change under various greenhouse gas emissions scenarios using convection-resolving simulations. The results provide strong support for robust future strengthening of intense tropical cyclones globally. We plan to add Hurricanes Harvey, Irma, and Maria to the investigation.