On the use of synthetic tropical cyclones and hypothetical events for storm surge assessment under climate change

This study presents a new approach to assess storm surge risk from tropical cyclones under climate change by direct calculation of the local flood levels using a limited number of events with an associated probability. The approach is based on the near-worst-case flood scenario, associated with a known tropical cyclone wind intensity probability (return period). We applied the method for the locality of Manzanillo, Colima, Mexico, using synthetic tropical cyclones derived from six different general circulation models for the present and future climates under the Representative Concentration Pathway 8.5. The synthetic events allowed the characterization of the wind intensity for the present and future climates for a given return period, as well as to determine the key tropical cyclones parameters related to storm surge. For Hurricane Patricia (2015), the strongest tropical cyclone to impact the region, we determined that its 95 m/s winds have a return period above 4000 years for the present climate and 198 years in a future climate scenario. Using Hurricane Patricia’s peak wind intensity, we created hypothetical events representing all possible approaches of tropical cyclones (211 events) to Manzanillo. We forced a hydrodynamic model with the hypothetical events over a mesh created with LiDAR-derived topography and then calculated the storm surge to create the near-worst-case flood scenario based on the maximum envelopes of water (MEOWs) and the maximum of MEOWs. Using those results, we created flood risk maps at city block level based on the combination of flood hazard and socioeconomic vulnerability maps. The presented method provides a tool for tropical cyclones storm surge hazard and risk assessment by generating near-worst-case flood maps under projected climates using a limited set of hypothetical events.