Tropical Cyclone Hazard Scale
Adequately reflecting the potential impact of tropical cyclones using the new Tropical Cyclone Hazard Scale.
Abstract: For decades, meteorologists and governments have been warning communities in coastal areas for an imminent tropical cyclone (TC) using the Saffir-Simpson Hurricane Wind Scale (SSHWS). The SSHWS categorizes a TC based on its maximum wind speeds, and has been used in defining evacuation strategies and humanitarian response. The SSHWS, however, only considers the TC’s wind hazard, whereas a TC can also cause major damage and harm through storm surges and extreme rainfall, inducing flooding. As a consequence, the SSHWS fails to mirror the TC’s total hazard potential. This becomes evident when looking at past events such as Hurricane Harvey (2017), which was classified as a Tropical Storm while it caused widespread flooding in the Houston (TX) area, with precipitation totals exceeding 1.5 m. Because of this, adequate risk communication can be challenging, as the public can (mistakenly) perceive a low-category TC as a low-risk TC. To overcome this weakness of the SSHWS, we propose the new Tropical Cyclone Hazard Scale (TCHS) that includes all three major TC hazards in its classification. The new scale preserves the categorization as used in the SSHWS, to maintain familiarity amongst the general public. In addition, we extend the TCHS with a Category 6, to support communication about the most extreme TCs. Applying the TCHS to an event set of high-impact historical landfalling TCs results in 26 TCs being classified as a Category 5 or 6, whereas only five of these were classified as a Category 5 on the SSHWS.