An every monsoon affair: How to tackle urban flooding
Urbanisation is inevitable as is climate change; the need is for a multi-pronged approach
As the monsoon hit cities, citizens were reminded of the mayhem that usually surrounds urban India around this time, where roads become canals, even if there is moderate rain.
Waterlogging — a prelude to urban flooding — is a common sight in urban India during the monsoon. Urban flooding has also become increasingly common, as the changing weather pattern resulted in more high intensity rain in fewer rain days.
The novel coronavirus disease (COVID-19) increased the problem of waterlogging as pre-monsoon desilting of drains was not carried out in full capacity.
There were several incidences of pluvial flooding in urban areas across India over the past decade. Some of these were a consequence of incessant rain over a day, for example, in Chennai and Mumbai in 2015 and 2005 respectively.
Others were a consequence of high-intensity bursts of downpour for three to six hours, suddenly overwhelming drainage systems. The trend of urban flooding and waterlogging has continued in urban India this year too.
July was the wettest month for Mumbai, which received 819 millimetres of rainfall on an average.
The city, however, received 675 mm of rain in the first five days of the month, with 427 mm on July 4, 2020, according to a report by international news channel Al Jazeera. This resulted in widespread flooding of roads and buildings in the city, with motorists wading through knee-deep water.
The National Capital Territory of Delhi received 74.8 mm of rainfall (recorded at Safdarjung) overnight on July 19, said a report by The Hindu newspaper. This resulted in widespread waterlogging in the city.
The downpour resulted in one person losing his life. Apart from that, all major junctions of the city were waterlogged. The city reported over 36 incidences of waterlogging and 14 instances of trees falling.
Context of urbanisation and climate change
It is important to note urbanisation is an inevitable process and urban areas will continue to grow demographically and spatially.
Cities — considered engines of growth — contribute more than 65 per cent of the national gross domestic product and provide employment to more than a third of the country.
The collateral damage emerging out of these expanding cities is the result of a breakdown in natural systems.
Urban areas, however, generate high volumes of polluted run-off, often resulting in the breakdown of the urban drainage system. In such a case, even moderate rainfall events can lead to flash floods in low-lying areas and can overwhelm drainage systems of cities.
It is evident that our weather patterns are altered because of global warming. There is evidence of change in some climate extremes based on data gathered from 1950, according to the Inter-governmental Panel for Climate Change (IPCC).
In terms of precipitation, it is likely there were statistically significant increases in the number of heavy precipitation events, according to the IPCC.
Projections revealed a significant increase in mean monsoon precipitation of eight per cent and a possible extension of the monsoon period.
Extreme excess and deficient monsoons are projected to intensify, according to a 2006 study published in ResearchGate. In the future, high intensity rain over a few rain days is expected to become normal.
Projected rainfall distribution pattern (a) in 2100 and (b) beyond 2100
Issues related to urban stormwater management
Deficiencies need to be identified under several structural and non-structural dimensions related to urban stormwater management.
Cities were not planned keeping in mind stormwater management. In most cases, development control regulations in master plans do not provide for run-off control measures.
Also, open spaces and water bodies are victims of ‘planned’ encroachments. Urban streams and water bodies are compromised for urban land uses. A section of the Barapullah drain in Delhi, for example, is covered to construct a bus depot.