A Multi-Scenario Analysis of the Storm Surge Hazard for Sri Lanka

Sri Lanka is vulnerable to storm surges due to cyclones generated mostly in the southern part of Bay of Bengal, and to a lesser extent, to those in the southeast of Arabian Sea. Accordingly, a statistical analysis of the historical events of tropical cyclones in the Bay of Bengal and in the Arabian Sea was carried out to identify cyclone scenarios with appropriate recurrence intervals representing short-, medium-, and long-term timescales. The time- and space-varying wind field was estimated by using the parametric cyclone model of Holland. Furtherr, a numerical model based on depth-averaged shallow water equations has been employed to simulate storm surges corresponding to each scenario. The model set-up was calibrated and verified by comparing the computed surge heights with those observed corresponding to the severe cyclones of 1964 and 1978 that made landfall in the east coast of Sri Lanka. As there is considerable uncertainty on the probable cyclone tracks including the landfall location, the storm surge simulations for each scenario was carried out for a large set of synthetic tracks that are in statistical agreement with the historical database. The computed maximum surge heights at every grid point corresponding to each of the above hazard scenarios was collated to form composite maps of peak surges over the entire model domain. The spatial distribution of the computed surge heights indicates that the level of the storm surge hazard is the highest for the northern province of Sri Lanka and the lowest for the southern province.