Urban Flooding

Why in news?

Due to climate change, urban population growth there has been increase in the urban flooding.

What is urban flooding?

• The flooding of land or property in a built environment, especially in densely populated cities where rainfall exceeds capacity of drainage system is known as urban flooding.
• It is a man-made disaster which is caused not only by higher precipitation but also by unplanned urbanization.
• Urban flooding is significantly different from rural flooding as urbanization leads to developed catchments, which increases the    
  • Flood peaks from 1.8 to 8 times and
  • Flood volumes by up to 6 times

What is the status of urban flooding in India?

• There has been an increasing trend of urban flood disasters in India over the past several years whereby major cities in India have been severely affected.
• Special feature in India
  • Heavy rainfall during monsoons
  • Storm surge affect coastal cities/ towns
  • Urban heat island due to global warming
  • Sea surge increase the level of sea in coastal cities

As per Ministry of Housing and Urban Affairs India will have 50% urban population by the end of 2050, so India must adopt sustainable practices to cope up the pressure.

What are the causes of urban flooding?

• Hydrological factors- It is caused by change in river course, presence of high tide and synchronisation of runoffs of various parts of watershed.
• Urban heat island- It resulted in increase in rainfall leads to flash flood which is a cause of concern in low lying areas and urban cities where the damage inflicted is huge.
• Sea surge- Storm surge due to tropical cyclones causes sea water to overflow into cities nearby coastal regions.
  • As per the Intergovernmental Panel on Climate Change (IPCC), it is estimated that before 2030, large parts of Kolkata could face immense flooding, causing the city to submerge.
• Concretisation- Building huge structures in urban areas leads to insufficient drainage infrastructure leading to urban flooding.
  • Example- 2021 Chennai flood.
• Pluvial flooding- It is a rain-driven flooding that results from the excess of natural or engineered drainage capacity.
• Deforestation- Trees act like a sponge that helps to hold soil.
• As trees are being cut down at a fast pace to make way for urbanisation to grow, more water runs towards a river during heavy rainfall and causes flood.
• Floodplain encroachment- This reduces the water carrying capacity of rivers which is brought from upper catchment areas and cause flooding.
  • One of the reasons for 2015 Chennai floods is floodplain encroachment.
• Drainage systems - Stormwater drainage systems in the past were designed for rainfall intensity of 12 – 20 mm.
• These capacities have been getting very easily overwhelmed whenever rainfall of higher intensity has been experienced.
• Unplanned release of water from dam-Kerala flood in 2018 is due to prolonged rainfall accompanied by unplanned release of water from Idukki dam.
• Climate change - Influence of urban microclimate and climate change are other factors.

Urban flooding is the highest reported climate hazard facing C40 cities with 92% of C40 cities experiencing flash or surface flooding due to rainfall or riverine flooding.

What are the consequences of urban flooding?

• Loss of life and property - Urban area has high population density and huge infrastructure.
• Every year, millions of people become homeless and washed away due to floods.
• Disruption of Communication-Flood causes damage to transportation links such as bridges, rail, power plants etc., thus causing communication disruption in those areas.
• Economic and Social Disruption- Urban area is the key centre for economic activity, the economy comes to a standstill as people are forced to move to another place.
• Hygiene- Detoriation of water quality which would result in the spread of communicable disease and water borne diseases.
• Epidemics- Waterborne diseases (cholera, typhoid fever, hepatitis) and vector-borne diseases (dengue, malaria) are caused due to floods.

What steps were taken to mitigate urban flooding?

• NDMA – After the Mumbai floods of 2005, NDMA has for the first time decided to address urban flooding as a separate disaster, delinking it from floods.
• Atal Mission for Rejuvenation of Urban Transformation (AMRUT)- It is an initiative to provide basic civic amenities to the urban areas to improve the quality of life.
• Smart Cities Mission- It is initiated to drive economic growth and improve the quality of life of people by enabling local development and harnessing technology as a means to create smart outcomes for citizens.
• HRIDAY Misison- National Heritage City Development and Augumentation Yojana which aims to conserve heritage, urban planning and increase the economic growth of the heritage cities.

What lies ahead?

• Legal Enforcement- India should enforce laws to check on encroachment of lands in the urban areas.
• Climate resilient structures- It should be in line with SDG 11-Sustainable cities and communities.
• Proper drainage infrastructure- Conduct monsoon audits regularly to mitigate the flood effects.
  • Tamil Nadu has appointed Tirupugazh Committee to recommend on flood mitigation.
• Greening cities -East Kolkata’s wetlands have been an effective flood defence mechanism that help treat a large share of the city’s sewage, produce half of the city’s fresh vegetables.
• Flood plain mapping- It improves flood management response and helps the community to understand their flood risk.
• Rain Water Harvesting (RWH) – Adopt RWH in all infrastructure constructions to ensure better water management.
• Bioswales- It must be constructed for percolation of rainwater into the ground.
• Blue-Green Infrastructure- It uses infrastructure, ecological restoration, and urban design to connect people with nature to solve urban and climate problems.

References

1. Down to Earth| India’s place in urban flooding
2. Down to Earth| Urban flooding management in cities
3. Down to Earth| North India urban flood
4. NDMA| Urban floods