Urban Flood Risk Assessment and Mitigation with InVEST-UFRM Model: a Case Study on Kolkata City, West Bengal State (India)

Urban flooding has become a widespread issue across the world over the last few decades, making it crucial for cities to prioritise the flood risk mitigation. Kolkata has been selected as the study area as this city is densely urbanised and waterlogging situation is frequent here. The main goal of this paper is to apply the Integrated Valuation of Ecosystem Services and Tradeoffs-Urban Flood Risk Mitigation (InVEST-UFRM) model for the city Kolkata to understand the flood-like situation after consecutive rainfall for 2 h with different rainfall depths and find possible mitigation measures. The result finds Kolkata is covered up with 75% impervious surface where more than 80% of the rain water transforms into runoff after 2 h of rainfall and northern portion of Kolkata is extremely vulnerable to flooding. About 47% flood volume increases by 71% with a change in rainfall depth. Open green spaces have the highest potentiality to retain rainfall. Average runoff retention capacity of watersheds reduces about 10% with increase in 50% increase in rainfall. Economic damage costs about 10 lakh rupees for the most vulnerable area of 5.45 km2 from the study area with a rainfall depth of 47 mm in 2 h. Flood risk related mitigation measures that should be followed for the study area with three perspectives like precipitation parameter, excess runoff reduction and runoff retention measures. Application of this model for urban flood mitigation is comparatively easy to use and more approachable for any urban area.