AbstractA storm surge–induced flood simulation methodology, called the GIS-based subdivision-redistribution (GISSR) methodology, is proposed for coastal urban environments. The methodology combines GIS with Manning’s equation to calculate the volume of water flowing into the geographical area under consideration and then redistributes it appropriately over that area. It uses as input the time histories of the storm surge height and of tides along the coastline. It is capable of incorporating a variety of protective measures along the coastline, such as seawalls. For flood simulations in the future, it is straightforward to account for a prescribed value of sea level rise. The GISSR methodology is extremely efficient, from a computational point of view, compared to existing flood simulation tools, such as GeoClaw or ADCIRC, which take several orders of magnitude more computing time because of the underlying complexity of their physical models. The methodology is found to be highly accurate by comparing its results to the actual extent of flooding observed during Hurricane Sandy in New York City (NYC). Several examples demonstrating its capabilities are provided involving different protective measures in NYC’s Lower Manhattan. The GISSR methodology is ideal for determining the optimal protective strategy for a coastal city because of its high computational efficiency since optimization requires a very large number of flood simulations.