A framework for risk-based assessment of urban floods in coastal cities

Many coastal cities in developing countries are at the risk of flooding due to a progressive increase in the built-up areas and poor management of storm water. The flooding situation in coastal cities gets accentuated further due to climate-induced natural disasters such as cyclones and climate change-induced sea-level rise that adversely impact the city's natural drainage potential. This study developed a composite urban flood risk index consisting of three sub-indices and 20 key natural, physical, social, and economic influencing variables for a coastal city (i.e., Cuttack) in eastern India, the intensity of storm run-off being one among the many. The intensity–duration–frequency curve developed shows that the city can experience floods with a peak discharge of 1320 cubic metre per second every alternate year for a rainfall intensity of 2-h duration. The urban flood risk index computed for all the city wards shows that out of the 59 wards, only one ward has low flood risk (index value < 0.40) and 20 wards are at high risk (index value 0.55 and above) from the urban flood. Thereafter, factors leading to high risk due to urban floods were identified and the institutional capacities available with the urban utility for fighting floods analysed.