Alternative point-wise metrics for tropical cyclone risks

To minimize the risks from tropical cyclones (TCs), the quantification and regular monitoring of TC activities are strongly needed. While the accumulated cyclone energy (ACE) (Bell et al., 2000, Climate assessment for 1999. Bulletin of the American Meteorological Society, 81, S1–S50) has been widely used for examining the level of basin-wide TC activities, the conventional ACE does not discriminate the regional characteristics of TC risks. By introducing a point-wise version of ACE, this paper proposes a geographical approach to the risk map for TCs. Here, the alternative metric is named the localized ACE (LACE), which interprets the TC risk directly felt by the local residents. Annual LACE at a geographical point measures TC activity by merging the quantities of frequency, intensity and duration factors, which contribute to the local TC activity in a year. In conjunction with LACE, a concept of LACE partial contribution (LACEP) is also proposed. The LACEP enables quantitative comparison of the contribution by each factor to the LACE, and thereby identifies the characteristics of the regional TC risks. To demonstrate the efficacy of the indices, that is, LACE and LACEP, this paper provides the response of the local TC activities to El Niño–Southern Oscillation in the western North Pacific and confirms the value of these indices.