Interpretation of the Knutson et al. (2020) hurricane projections, the impact on annual maximum wind-speed, and the role of uncertainty

Knutson et al. (BAMS 101:E303–E322, 2020) combined results from many studies to produce distributions of how tropical cyclone frequency and average intensity may change in the future. These distributions can be applied to risk models by using them to simulate multiple realisations of possible changes in future storm climate. Ideally the simulations would be performed to maintain consistency between the changes in frequency and average intensity, but it is not obvious how to do that, or whether it is even possible. Considering North Atlantic cyclones, we test three methods for simulating from Knutson et al. and find two that are consistent and one that is not. Using the best of the methods we find that there are no future scenarios in which weak storms increase in frequency while very intense storms decrease in frequency. We then apply changes in frequency and average intensity to a risk model for annual maximum intensity. After integrating over the uncertainty, we find that on a conditional basis all storms become more intense under climate change, and that the annual probability of the most intense storms increases by 19%. Annual maximum intensity decreases at intermediate levels of intensity as a result of the non-linear propagation of uncertainty. We also show that the changes in risk implied by the Knutson et al. results cannot be well approximated if the propagation of uncertainty is ignored. Future work should involve updating these results with tropical cyclone projections from the latest high-resolution climate models.