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Urban Flooding

GS Paper  3

Syllabus: Disaster Management/Geography


Source: Indian Express

 Direction: Twice, UPSC has asked similar Qn on Urban flooding in Mains. Remember recent examples, causes and a few recommendations on urban flooding.

 Context: There was unprecedented flooding in India’s tech capital Bengaluru.

Urban Flooding is an inundation of land in a constructed setting, particularly in densely populated areas.

      • Previous such flooding incidents: Kochi, Mumbai, Hyderabad and Chennai.



      • Higher rainfall: As per the IMD, monsoon has become frequent and unpredictable
      • Storm surges (for coastal cities): E.g. Cyclone Amphan in 2020 flooded the streets of Kolkata. Within eastern India, the storm killed 98 people and caused $13.8 billion (2020 USD).
      • Groundwater levels: In Chennai, the replenished groundwater table across the city after rains becomes a challenge for several buildings with basements.



      • Encroachment: A large number of wetlands that soaked up the rainwater has encroached. Bangalore had 262 lakes in the 1960s; now only 10 of them hold water.
      • Rapid and unplanned urbanization: In Bengaluru, stormwater drains were not directly connected to its water bodies. In some places, the runoff water was flowing into constructed deviation canals. CAG found that this increased the chances of flash floods.
      • Destruction of mangroves: Mumbai lost about 40% of its mangroves between 1995 and 2005.
      • Poor civic management of storm water drainage: CAG report (last year) pulled up Bengaluru municipality for this poor management.
      • Lack of data: CAG also found that the Bengaluru municipality did not maintain proper records of the stormwater management funds allotted to it under the JNNURM.
      • Lack of coordination: CAG report also noted the lack of coordination between the municipality and the Bangalore Development Authority on drainage-related matters.


Steps to mitigate urban flooding:

      • Sponge Cities Mission: The idea of a sponge city is to make cities more permeable so as to hold and use the water which falls upon them.
      • Atal Mission for Rejuvenation and Urban Transformation (AMRUT
      • Stormwater disposal system: The Brihanmumbai Storm Water Disposal System or BRIMSTOWAD, the project to overhaul Mumbai city’s old stormwater drainage system was started after the 2005 deluge.
      • Water-sensitive urban design (WSUD in Australia): regards urban stormwater runoff, and waste water as a resource rather than a nuisance or liability.
      • Bioswales or ‘Rain Garden’ (New York): are landscape features that collect polluted stormwater runoff, soak it into the ground, and filter out pollution.


Therefore, there is a need to include public open spaces within the urban fabric in the form of storm management infrastructure, which could help our cities transform into water-sensitive cities.


Insta Links

Urban Floods


Mains Link

Q. How unplanned development and disregard for natural water bodies cause frequent urban flooding in Indian cities. What can we learn from other countries in an attempt to address the Urban flooding in India? (15M)


Prelims link

Link it with the retreat of the Monsoon, the impact of La Nina and IOD on monsoon rains.

With reference to Ocean Mean Temperature (OMT), which of the following statements is/are correct? (UPSC 2020)

      1. OMT is measured up to a depth of 26°C isotherm which is 129 meters in the southwestern Indian Ocean during January-March.
      2. OMT collected during January-March can be used in assessing whether the amount of rainfall in monsoon will be less or more than a certain long-term mean.

Select the correct answer using the code given below:

(a) 1 only

(b) 2 only

(c) Both 1 and 2 only

(d) Neither 1 nor 2

Answer: B

Ocean Mean Temperature (OMT) is measured up to a depth of 26 degrees isotherm. It is measured with the help of satellites that orbit the earth. In the Indian ocean, OMT is analysed by measuring the ocean thermal energy during the period from January to March.

With reference to ‘Indian Ocean Dipole (IOD)’ sometimes mentioned in the news while forecasting Indian monsoon, which of the following statements is/are correct? (UPSC 2017)

      1. IOD phenomenon is characterised by a difference in sea surface temperature between tropical Western Indian Ocean and tropical Eastern Pacific Ocean.
      2. An IOD phenomenon can influence an EI Nino’s impact on the monsoon.

Select the correct answer using the code given below:

(a) 1 only

(b) 2 only

(c) Both 1 and 2

(d) Neither 1 nor 2


Answer: B

The Indian Ocean Dipole (IOD) is defined by the difference in sea surface temperature between two areas (or poles, hence a dipole) – a western pole in the Arabian Sea (western Indian Ocean) and an eastern pole in the eastern Indian Ocean south of Indonesia.