Flash Flood Vulnerability in India

Context

A recent study by researchers at IIT Gandhinagar, published in Nature, analysed flash flood patterns in the Indian subcontinent, identifying highly vulnerable river basins and key driving factors.

Flash Flood Hotspots:

Most flash floods occur in the Himalayan, Central Indian, and West Coast regions.
The Brahmaputra, Narmada-Tapi, Mahanadi, Godavari, Ganga, Mahi, Krishna, and Indus river basins have been identified as either “extremely prone” or “highly susceptible” to flash flooding.

Increase in Flash Flood Events:

Flash flood events in India increased from 132 in 2002 to 184 in 2020 (as per official figures).
Notable increases observed especially in the Brahmaputra basin, followed by Ganga and Krishna basins since 1995.

Driving Factors:

Only 25% of flash floods are triggered solely by extreme precipitation.
Remaining 75% result from compound effects:
- High antecedent soil moisture,
- Prolonged heavy rainfall,
- Rapid rainfall event after wet soil saturation.

Role of Climate Change:

Between 1981–2020, rise in extreme rainfall frequency due to warming trends.
Every 1°C increase in temperature raises moisture-holding capacity by 7%, causing more intense precipitation

Geomorphological Factors:

Steep slopes and high relief in Himalayan and Western Ghats sub-basins contribute to faster runoff and flood onset.
In central India, flashiness is driven more by rainfall concentration.

Adaptation and Mitigation:

Calls for basin-specific strategies based on rainfall intensity, soil type, slope, and geomorphology.
Importance of resilient infrastructure, early warning systems, and region-specific adaptation planning