UPSC Mains 2024 GS3 Q18: model answer

Urban floods are different from river floods: they rise quickly from intense rain on sealed surfaces and can paralyse a city in hours.

Causes

• Climate: more frequent extreme rainfall events; cloudbursts and sea level rise in coastal cities.
• Encroachment on lakes, wetlands and floodplains.
• Old and choked drains, solid waste blocking them.
• Concrete surfaces reduce infiltration.
• Poor reservoir release coordination and weak forecasting.

Two major floods

• Mumbai, July 2005: about 944 mm of rain at Santacruz in 24 hours; Mithi river overflowed; over 1,000 deaths in Maharashtra; the city stopped for days. It led to the BRIMSTOWAD drainage upgrade.
• Chennai, December 2015: extreme rain in the north-east monsoon plus late release from Chembarambakkam reservoir; encroached lakes failed to absorb water; hundreds died and losses were huge.

Policies and frameworks

• NDMA Guidelines on Management of Urban Flooding (2010): a separate approach from riverine floods.
• Disaster Management Act, 2005 and National DM Plan.
• Standard Operating Procedure for urban flooding (MoHUA, 2017).
• AMRUT storm water drainage; Smart Cities Mission.
• Urban Flood Risk Mitigation Programme (2023) for seven big cities.
• Early warning systems like Chennai's C-FLOWS and Mumbai's IFLOWS-Mumbai.

Cities must learn to hold water, not just drain it: wetland restoration and sponge city design are the way forward.