Tropical Cyclone Storm Surge

Overview

Tropical cyclone storm surge is a change in the water level compared to the standard water level, induced by tropical cyclones/hurricanes/typhoons. Tropical cyclone storm surge can be one of the most damaging aspects of tropical cyclones, especially in regions where buildings are designed to withstand tropical cyclone wind speeds. Additionally, storm surges can cause significant loss of life. Storm surge itself is separate from the additional, compounding effects of storm tide (storm surge + tide) and the impact of waves. Two main effects contribute to storm surge. The first, is the development of a fetch - an area where winds are relatively constant in both direction and speed, which pushes water in one direction. The fetch causes a rise in sea level due to forcing water toward the shore. The second effect is that of pressure - tropical cyclones are deep low-pressure systems. ‘Barometric uplift’, or the inverse barometer effect approximately causes a 0.01 m rise in sea level for every 1 hPa drop in pressure. The Tropical Cyclone Storm Surge (TCSS) developed for the Climate Risk Engines aims to capture both of these effects by utilising the results of the tropical cyclone wind model. As TCSS is a rise in local sea heights, the future change in sea level will also affect future TCSS heights. This is in addition to changes in TCSS due to increasing tropical cyclone intensity alone

Local Context Data Use

Data is used by the model to calculate wind-driven surge including bathymetry data. Tectonic adjustments are calculated and used to modify sea level rise projections.

Baseline Hazard Data

There are multiple hazard datasets used in this model including wind-driven surge, fetch length, drag coefficient, pressure-driven surge, wind speed-pressure relationship, inverse barometer effect, liner regression factors & sea level rise and tectonic adjustments. These datasets include: • Wind-driven Surge • Fetch Length • Drag Coefficient • Pressure-driven Surge • Wind speed-pressure (WPR) Relationship • Inverse Barometer Effect • Sea Level Rise and Tectonic Adjustments (SLR)

Climate Change Projections

As the model uses the tropical cyclone wind model, sea surface temperature data is one of the climate projections used by TCSS. Gridded projections of sea surface temperatures, based on GCMs from CMIP6 are used to project the change in tropical cyclone wind speed distributions, which are then used to calculate the change in storm surge height. The storm surge height is then modified by projections of sea level rise and land rise.