Context

• A new study by researchers at IIT Gandhinagar has warned that flash floods are becoming more frequent and severe across India. 

About the Study and its Findings

• The study, ‘Drivers of flash floods in the Indian sub-continental river basins’, identifies the Himalayas, western coast, and Central India as key hotspots, using hydrological and geomorphological data to map sub-basin susceptibility. 
• In the Himalayas, steep terrain and elevation drive flood risk, while in the West Coast and Central India, rapid runoff—termed “flashiness”—plays a key role. 
• The study finds that nearly 75% of flash floods result from a combination of extreme rainfall and already saturated soil, with only 25% due to precipitation alone.

Key Drivers behind Flash Floods In India

• The study reveals that only 25% of flash floods in India are caused solely by extreme rainfall. 
• Most incidents result from a combination of heavy precipitation and pre-existing soil saturation. 
• When the ground is already wet, it cannot absorb additional rainfall, leading to rapid runoff and increased flood risk.
• Notably, only 23% of extreme rainfall events trigger flash floods within six hours. Instead, prolonged periods of both low- and high-intensity rain are more likely to cause such disasters.
• The study also highlights regional variations. 
• In the western coast and Central India, sub-basins react quickly to rainfall due to their high “flashiness” — the tendency of water levels to rise rapidly. 
• In the Himalayan region, steep terrain and high relief further elevate the risk. 
• Within major river basins like the Ganga, flash flood susceptibility differs — sub-basins in the southern Himalayan stretch are more prone, while central areas show lower risk.

About Flash Floods

• Flash floods are sudden, intense floods that occur within six hours of a heavy rainfall event, usually in regions with steep slopes, poor drainage, or saturated/dry soil. 
• Unlike riverine floods, they offer little warning, making them particularly deadly.

Impact of Flash Floods

• Human and Livelihood Impact: Flash floods lead to significant casualties due to their sudden onset.
• The 2023 flash floods in Himachal Pradesh claimed over 400 lives and displaced thousands.
• Damage to Public Utilities: Flash floods damage power lines, drinking water systems, and mobile networks, making post-disaster recovery slower and more expensive.
• Land Degradation: Torrential runoff erodes topsoil, degrades fertility, and increases sedimentation in rivers and reservoirs.
• Urban Challenges: Cities like Mumbai, Hyderabad, and Bengaluru experience rapid runoff due to concretised surfaces and encroached stormwater drains.

Initiatives by Government 

• Central Water Commission (CWC) is the nodal organisation entrusted with the task of flood forecasting & early flood warnings in the country.
• Indian Meteorological Department (IMD) in joint collaboration with the US National Weather Service, has developed a Flash Flood Guidance System (FFGS) for the South Asian region.
• The Central Government has approved the National Glacial Lake Outburst Flood Risk Mitigation Programme (NGRMP) in four Himalayan States viz. Himachal Pradesh, Uttarakhand, Sikkim and Arunachal Pradesh with a total budget of Rs.150.00 crore.