It includes drains, pumps and outfalls. They frequently overflow by heavy rainfall or high levels of storm-water runoff from roads and streets. Indian cities like Bengaluru, Bihar, Delhi, Mumbai and Hyderabad are flooding frequently. There are multiple, recurring failures of grey infrastructure in India and other developing countries, for which alternatives are now being sought.
Natural ecosystems such as lakes, parks, floodplains, forests are nature-based solutions called blue-green infrastructure and offer low-cost and flexible solutions for flood mitigation and management. They offer many other co-benefits.
Urban flood management in India continues to focus only on improving grey infrastructure, rescue and relief, instead of creating sustainable solutions. Cities continue to expand storm-water networks, clean channels and separate the sewage and storm-water drains. These are all important actions and urban areas bear high expenses to build grey infrastructure; but repeated floods mean that these actions are not sufficient.
Major reasons for frequent urban flooding across India
1. Construction on flood pathways.
During the monsoon, urban development and infrastructure such as roads, airports, bus depots, metro rail, etc. which are built on low-lying areas such as floodplains and lake beds, face higher risk of floods.
2. Making way for the floodwater.
Water penetrates into the ground, flows as surface runoff, evaporates and transpirate into the atmosphere. Urban regions with impenetrable surfaces, avoid water to go underground, decrease evaporation and transpiration. This highly increases surface runoff. Urban India is constantly building structures, streets, flyovers for urban citizens, frequently with inadequate storm-water infrastructure. Enormous volumes of storm-water deteriorate on these impenetrable surfaces, causing continued flooding.
3. Climate change and uncertainty.
The adverse climate change is creating uncertainty in many environmental phenomena. Rainfall variability is increasing because of climate change. Average monthly rainfall is now falling within days. Floods have high economic and social damage. This year (2020) Mumbai had 80% of its average rainfall in eight days.
Forecast, response and resilience.
- Both grey and blue-green infrastructure expansion and upgrade is needed.
- Official response to floods needs high-tech rainfall and flood warning systems like in Chennai and Mumbai.
- Cities are building interactive maps of flood-prone zones (Bengaluru).
- These measures enable evacuation and support effective deployment of rescue and relief measures, but do not prevent floods and mitigate against loss to life, property and infrastructure.
- A reassessment of storm-water and cloudburst management is urgently needed in India. Depending solely on last century’s inflexible, expensive grey infrastructure does not manage current and future extreme natural events. Studies prove that the green infrastructure for storm-water management are cheaper and have more co-benefits than upgrading or expanding grey infrastructure.
- Along with flood planning, we need major steps towards climate change and environmental protection. Much of the adverse natural and man-made events are happening because of collective ignorance towards climate and environment.