The frequency of urban floods due to high intensity rainfall is increasing over the years. Discussing the…

Question

The frequency of urban floods due to high intensity rainfall is increasing over the years. Discussing the reasons for urban floods, highlight the mechanisms for preparedness to reduce the risk during such events.

Ghissu Editorial · Accepted Answer

Urban floods are rising because heavier rain bursts meet undersized, choked drains and cities built over lakes, wetlands and floodplains. Preparedness rests on NDMA's 2010 Urban Flooding Guidelines, ward-level plans, early warning such as IFLOWS-Mumbai, drainage upgrades and sponge-city restoration.

**Introduction**

Mumbai's 944 mm of rain on 26 July 2005 and Chennai's 2015 deluge show how short bursts of extreme rain paralyse Indian cities. NDMA notes that urbanisation raises flood peaks 1.8 to 8 times (NDMA, 2010).

**Reasons Behind Rising Urban Floods**

SKETCH: fishbone | Why Indian Cities Flood
effect: Urban flooding
- Intense short bursts
- Choked, undersized drains
- Lakes and wetlands built over
- Concrete, impervious cover
- Floodplain encroachment
- Unplanned reservoir release

1. **Heavier, shorter rainfall**: A warmer atmosphere and the urban heat island concentrate rain into intense bursts over the city core.
2. **Drains built for another era**: Storm drains cover only about 20% of urban roads (MoUD, 2011), and Mumbai's colonial drains were sized for about 25 mm an hour, then choked by plastic and silt.
3. **Lost natural sponges**: Chennai built over the Pallikaranai marsh, and Delhi's built-up area rose from 20% in 1985 to 52% in 2018 (NIDM, 2025), so more rain runs off.
4. **Mismanaged releases**: The late, bulk release from Chembarambakkam reservoir deepened Chennai's 2015 flood.

**Mechanisms for Preparedness to Reduce Risk**

1. **Institutional plan**: NDMA's Urban Flooding Guidelines (2010) seek ward-level contingency plans, now backed by Urban Disaster Management Authorities under the DM (Amendment) Act 2025.
2. **Early warning**: Doppler radars, dense rain gauges and IFLOWS-Mumbai (2020) give ward-wise inundation forecasts.
3. **Drainage upgrades**: Pre-monsoon desilting and higher design standards, as Mumbai's BRIMSTOWAD project raised drain capacity towards 50 mm an hour.
4. **Sponge city and community**: Restored lakes, rainwater harvesting and trained ward volunteers cut runoff and response time.

**Conclusion**

Cities flood because they have paved over their own drainage as rain intensifies. Warning, drains, wetlands and ward-level planning, in the spirit of the Sendai Framework, make the monsoon a manageable risk.

The frequency of urban floods due to high intensity rainfall is increasing over the years. Discussing the reasons for urban floods, highlight the mechanisms for preparedness to reduce the risk during such events.

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