From hazard to impact: flood damage assessment tools for mega cities

In this paper, a set of GIS-based tools is presented that combines information from hydraulic modelling results, spatially varied object attributes and damage functions to assess flood damage. They can directly process the outputs of hydraulic modelling packages to calculate the direct tangible damage, the risk to life, and the health impact of individual flood events. The tools also combine information from multiple events to calculate the expected annual damage. The land cover classes from urban growth models can be also used in the tools to assess flood damage under future conditions. This paper describes the algorithms implemented, and the results of their application in the mega city of Dhaka in Bangladesh. Complications and technical issues in real-world applications are discussed, and their solutions are also presented. Although it is difficult to obtain reliable data for model validation, the sensitivity of the results to spatial resolution and input parameters is investigated to demonstrate that the tools can provide robust estimations even with coarse data resolution, when a fine masking cell size is used. The tools were designed to be flexible, so that they can also be used to evaluate different hazard impacts, and adopted in various GIS platforms easily.