From June 1 to September 30, Bengaluru urban district recorded 468 mm rainfall against the normal of 471 mm. Although the rise is not significant, the rainfall this year has not been uniform with some months recording more than average rainfall. Even in the month of October, the city is receiving heavy rainfall, presumably more than other years.
The wet spells are also leading to a few pockets in the city to go under water, with at least one rain-related death being reported in the city. Here’s why Bengaluru has been receiving heavy rainfall.
Why is Bengaluru receiving heavy rainfall in October?
An official at the IMD told The Indian Express that the trough between cyclones over Bay of Bengal and Arabian Sea have resulted in the heavy downpour in October. “The trough is passing through North interior Karnataka. The low pressure developing in the Bay of Bengal is also contributing to this. In the next 48 hours, Bengaluru will receive thunderstorms. Every year during the month of October and November we witness a similar situation.”
The IMD has already recorded 1,006 mm of rainfall against an annual average of 986.9 mm.
According to the Karnataka State Natural Disaster Monitoring Centre (KSNDMC) the state receives an annual normal rainfall of 1,153 mm out of which the Pre-Monsoon season contributes about 10 per cent, the South-West Monsoon season contributes about 74 per cent and the North-East Monsoon season contributes to about 16 per cent. During 2020, the state had recorded 1,301 mm rainfall.
What difficulties did passengers at the airport face?
A weatherman at the India Meteorological Department (IMD) said since the launch of the observatory at the international airport in 2011, the highest rainfall was recorded on October 11. Bengaluru airport, which received 178.3 mm of rain on Monday, has now come to a standstill as areas near the pick-up and drop points are flooded. As many as 11 departing flights were delayed due to weather conditions. The waterlogging at the Central Industrial Security Force (CISF) junction pressed airport authorities to redirect traffic.
Some passengers shot videos of taking tractors to embark on their journey to the airport and navigating with great difficulty at the airport which turned into a cesspool. A passenger from Bengaluru to Guwahati, Vivek Gupta, said he almost missed his flight due to the mayhem owing to the rain.
“A car turned upside down and the streets looked like swimming pools. My luggage was completely wet in the rain. I had never witnessed such a scene at the airport ever,” he added.
While questions were raised over the drainage system at the airport, the Bangalore International Airport Limited (BIAL) spokesperson commented that since its start of operations in 2008, the airport has not seen such unprecedented rain on a single day. BIAL denied any fault with the design of drainage structures.
A very heavy downpour of unprecedented rain on the evening of October 11, 2021 caused waterlogging in parts of the Kerb side of Kempegowda International Airport in Bengaluru.
“Although the drainage system in the Kerb area is working well, the sudden high intensity rain caused waterlogging for a short duration. Our team was immediately pressed into action and the issue has been resolved. There was waterlogging at one of the junctions and our traffic staff were present to redirect traffic,” the spokesperson added.
BIAL also claimed that in order to avoid wastage of water within its premises, drains were built to direct excess water flow to Bettakote lake adjacent to the airport.
What do the past records of rainfall in October say?
According to the IMD, every year during the month of October and November, Bengaluru receives heavy rainfall. Data shows that in October 2005, Bengaluru received 605.6 mm of rainfall. On October 6, 2017, Bengaluru witnessed 76.6 mm of rainfall in 24 hours and 385.7 mm of rainfall for the entire month, leading to massive flooding of low-lying areas.
The heaviest rainfall in 24 hours was 178.9 mm on October 1, 1997. On May 06, 1909, the city received 153.9 mm rainfall. The monthly average rainfall in the months of October have been — 204.3 mm in October 2020. October 2019 saw 178.4 mm rain, 111.7 mm rain was recorded in October 2018 and 343.8 mm of rainfall in October 2014.
Is increasing concretisation in the city leading to flooding?
With the threat of heavy rainfall and flooding looming over the state, the municipal agency, Bruhat Bengaluru Mahanagara Palike, has identified 209 areas prone to flooding out of which 153 were sensitive and 53 were extremely sensitive. Parts of Bengaluru like J P Nagar, Puttenahalli, BTM, Koramangala and Ejipura, which fall in the low-lying areas, witness flooding.
However, experts have pointed out that the BBMP did not take action on the reports.
Scientist at Indian Institute of Science (IISc) Dr T V Ramachandra had reiterated that a poor drainage system, clogged drains with solid waste and building demolition wastes, encroached drains, unscientific remodelling, which includes narrowing and concretisation of drains, loss of interconnectivity among lakes (with poor drainage network — encroachment of drains) and encroachment of buffer zones (lakes, drains) are the major reasons behind flooding of the city.
Sharing his expertise, Ramchandra said that the storm-water drain connecting Bellandur Lake from city market has narrowed to 28.5 m against the original width of 60 m, thereby, violating NGT guidelines of maintaining the physical integrity of SWDs and buffer zones.
“The concretization and narrowing of the drains have only enhanced the flooding in the city. Moreover, this affects the hydrological functional ability of the storm. If the drains are concretized, the velocity of water increases which further enhances the chance of flooding in the area. As the paved area increases – for example, due to vegetation clearing, new housing or industrial developments, urban infill, paving driveways, patios, new roads etc, so does the amount of runoff,” the study says.
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Why do some parts of Bengaluru receive heavy rains and others less?
The primary rainy season is from June to October when Bengaluru receives rain from the South-West Monsoon. In this period, the city is vulnerable to floods. KSNDMC looked at the rainfall pattern of Bengaluru between two periods – 1960-1990 (named P1), and 1991-2017 (P2). The study revealed that the average annual rainfall in the Bengaluru Urban district has increased by 107 mm – from 836 mm to 943 mm in the period.
Officials at IMD say that due to increased urbanisation, the radiation of excess heat in the city contributes to the development of clouds. Pollution also contributes to the variation of rainfall patterns in the city. Even the temperature in the city varies. South and East Bengaluru have large pockets of industries, IT companies and residential houses which results in high temperatures.
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