How flash floods are affecting India

Flash floods lead to the death of more than 5,000 people annually in India. With soaring global temperatures, they are expected to increase in frequency and become more intense. 
Study on Flash Floods in India

• An IIT Gandhinagar study mapped flash-flood vulnerability at the sub-basin level using hydrological and geomorphological data.
• Himalayan risk is driven mainly by steep slopes and high elevation, while western and central regions are vulnerable because of rapid runoff or high “flashiness.”

Key Findings

• Only 25% of flash floods are caused by extreme rainfall alone.
• Nearly 75% result from heavy rainfall combined with already saturated soil.
• Only 23% of extreme-rainfall events trigger flash floods within six hours; prolonged rainfall is often more decisive.
• More than 75% of flash floods during 1980–2018 occurred in the monsoon season.

Impact of Climate Change

• A warmer atmosphere can hold nearly 7% more moisture for every 1°C rise, increasing intense rainfall.
• Between 1981 and 2020, extreme rainfall increased by:
  • 100% during pre-monsoon
  • 56% during monsoon
  • 40% during post-monsoon
  • 12.5% during winter
• Flash floods have increased sharply since 1995, particularly in the Brahmaputra, Ganga and Krishna basins.

Emerging Risk Areas

• Previously low-risk basins are becoming more vulnerable due to changing rainfall and streamflow patterns.
• Among non-prone sub-basins:
  • 51% recorded increased rainfall
  • 66.5% recorded higher streamflow
• This indicates that climate change may create new flash-flood hotspots.

Way Forward

• Develop region-specific early-warning systems based on rainfall, soil saturation and terrain.
• Identify emerging hotspots and strengthen climate-resilient infrastructure.
• Improve land-use planning, watershed management and integrated flood-risk governance.
• Shift from rainfall-only forecasting to sub-basin-level vulnerability assessment.