An Index for Cyclone Damage Potential

Traditionally, cyclone intensity has been emphasized in communicating damage potential to vulnerable communities. The US Saffir-Simpson code breaks hurricane intensity into five categories and has proven to be an effective and popular approach, with similar categorizations adopted in other cyclone warning regions.

However, cyclone intensity alone does not fully explain the damage potential of a tropical cyclone. A number of studies have demonstrated the importance of size and duration of strong winds (e.g. Czajkowski and Done 2014 and Jain 2010). Many specific cases also have can readily be found where the contribution from size and duration has been considerably greater than intensity in causing observed damage (e.g. Sandy).

Here we present an approach to assessing damage potential that includes all three components, the index for Cyclone Damage Potential, or CDP:

CDP=4 [(v_m/65)^3+5(R_h/50)]/v_t

vm is the maximum wind speed, Rh the radius of hurricane-force winds, and vt is the translation speed. Nautical units are used, the CDP is normalized to extend from 0-10, and for vt<5 kt set vt=5.

The CDP provides a first-order assessment of damage potential arising from winds, sea state and storm surge, but not rainfall. It does not refer to actual damage but is intended to provide easily communicated indications of the relative damage potential for individual storms or for collections of storms over defined regions or seasons. Actual damage assessment and prediction requires an assessment of vulnerability.

The presentation will describe the rationale behind the parameter selection and provide example uses comparing historical tropical cyclones, for basin and inter-basin comparison, and as an indicator of the impact of climate variability and change.