4. Mapping Tropical Cyclone Energy as an Approach to Hazard Assessment

Tropical cyclones (TCs), specifically their higher energy equivalents of hurricanes or typhoons, are the focus of great concern over their destructive impacts on coastal regions; this concern was enhanced as the trio of hurricanes (Harvey, Irma, and Maria) imposed spectacular damage and economic losses to parts of the United States and the Caribbean in 2017. We investigated historical TC events from the Western North Pacific and North Atlantic basins and introduced a new energy-based approach to mapping and spatially assessing TC hazards in both basins. By combining the energy index (EI) simplified from the power dissipation index (PDI) with a weighted density mapping tool, we defined a spatial energy cell which delineated a zone of intense TC energy loss. The energy cell we identified from the TC hazard map represents historical hot spots of TC events with reference to both frequency and intensity. We show that as TCs in Western North Pacific move westward from the source energy cell, energy is dissipated very rapidly over the Philippine land mass forming a dramatic energy discontinuity which we term an energy cliff. The migration of energy cells in the North Atlantic reflects inter-decadal variations of TC activity. Finally, the concept of energy dissipation discussed in this paper could be employed as a basis for the energy-based comparison of the magnitudes of all categories of natural hazards and help illuminate the nature of hazard-impact relationships.