Follow the rains, not the calendar, to fight floods, Pg11

Key Highlights:

• Urban areas in India are experiencing increased flooding due to untimely and intense rainfall, even in months like September.
• A study shows that about 64% of Indian tehsils have seen a rise in heavy rainfall days by 1-15 days.
• Floods in the last two decades have caused the most loss to life and property from natural disasters in India, with single flood events causing damages of some ₹8,700 crore.
• The Council on Energy, Environment and Water (CEEW) analysis shows that one-hour rainfall in Thane now reaches 50 mm once every two years, and about 80 mm per hour once every 50 years.

Detailed Insights:

• Indian cities are designed for a climate that no longer exists, leading to inadequate preparedness for the changing patterns of rainfall.
• The cleaning of storm water drains and municipal solid waste management should be aligned to prevent waste from blocking drains and exacerbating flooding.
• City authorities should incorporate sub-daily rainfall analysis into city monsoon planning and integrate recent patterns and short-duration, high-intensity rainfall events into infrastructure design.
• The India Meteorological Department (IMD) rainfall alerts should trigger joint sanitation drives and drain inspections in vulnerable areas, improving coordination between departments.
• City authorities must update Intensity, Duration, Frequency (IDF) curves every 5-10 years to ensure that infrastructure keeps pace with evolving rainfall patterns.
• Drainage design should be based on micro-catchment-level hydrological analysis that accounts for topography, which affects peak discharge during storms.

Key Concepts Involved:

• Intensity, Duration, Frequency (IDF) curves: Statistical tool used to estimate the probability of extreme rainfall events of specific durations and intensities.
• Sub-daily rainfall analysis: Examination of rainfall patterns at intervals shorter than 24 hours to understand short-duration, high-intensity rainfall events.
• Micro-catchment-level hydrological analysis: Assessment of water flow and drainage at a small, localized scale, considering topography and other factors.