BharatNotes What is Urban Flooding?
Urban flooding occurs when rainfall in a city outstrips the capacity of its stormwater drainage network, causing water to accumulate on streets, in basements and in low-lying colonies. It differs fundamentally from riverine flooding: it is driven by intense local rainfall over impervious (concretised) surfaces that generate rapid, high-volume runoff, and can strike even where no river exists. Recognising this distinction, the NDMA's National Guidelines on Management of Urban Flooding (September 2010) for the first time de-linked urban flooding from riverine floods and treated it as a separate disaster.
Why It Happens
The drivers are largely man-made and structural:
| Cause | Explanation |
|---|---|
| Unplanned urbanisation | Concretisation cuts infiltration and sharply raises surface runoff |
| Loss of water bodies | Encroachment of wetlands, lakes and natural drains removes natural sinks |
| Ageing/undersized drains | Many systems were designed for rainfall of only ~12-20 mm/hr and are easily overwhelmed |
| Poor maintenance | Silted, garbage-choked drains do not work to designed capacity |
| Climate change | More frequent high-intensity, short-duration rainfall events |
Major Indian Episodes
- Mumbai (26 July 2005): ~944 mm of rain in 24 hours; over 900 deaths — the trigger for India's dedicated urban-flood policy thinking.
- Chennai (2015): Heaviest rainfall in over a century; 500+ deaths and damages widely reported above ₹15,000 crore.
- Hyderabad (October 2020) and Bengaluru (29-30 August 2022): Large parts of each city submerged after record rains, exposing the same pattern of lost lakes and choked drains.
Management Framework
The NDMA 2010 Guidelines remain the policy backbone. Key recommendations include:
- A National Hydro-meteorological Network (with the Central Water Commission and IMD) for real-time monitoring and early warning.
- Urban Flooding Cells at state nodal departments and urban local bodies (ULBs).
- Catchment as the basis for designing stormwater drains, with watershed- and ward-based drainage inventories.
- Mandatory rainwater harvesting in buildings and rain gardens/permeable surfaces for on-site stormwater management.
Complementing this, AMRUT 2.0 (launched 1 October 2021 by the Ministry of Housing and Urban Affairs, for FY 2021-22 to 2025-26) funds stormwater drainage and rejuvenation of urban water bodies to reduce flooding.
UPSC Angle
Examiners value answers that distinguish urban from riverine flooding, name the NDMA 2010 Guidelines and AMRUT 2.0, and integrate structural measures (drainage upgrades, retention basins, permeable surfaces) with non-structural ones (early warning, floodplain zoning, restoring wetlands, sponge-city concepts). Linking specific city case studies to the underlying governance and climate drivers consistently scores well.
