Integrating green & grey essential to mitigate urban floods

Flood events are a part of nature, but urbanisation, which goes hand-in-hand with land-use changes, makes cities impassable for excess water, thereby often aggravating urban flooding. Inspite of efforts made by society and governments to reduce flood risks and losses for decades, people in Indian cities have been forced to find various ‘zugaad’ and adapt to the tormenting challenges that all kinds of flood events bring. While the cities keep growing, administrators and politicians are yet to shift their vision from industrial development to saving their cities and community

In addition to hindering the lives of people and blocking people’s access to basic services, floods continue to damage public and private properties, which become a major economic liability for lower and lower-middle income nations . Due to lack of proper, carefully thought out development of our urban spaces, our cities now have a lot of impervious surfaces and blockages to the natural hydrology of a landscape.
Mitigating urban floods are possible with green infrastructure built on natural designs like rain garden, green roofs and green walls, concrete product that can absorb rainwater and storm water, thus channeling it into the ground. However, Seema Mundoli, Faculty at Azim Premji University, who has expertise in the field of sustainable urban development, in an interview with the Team Urban Update, said that such concepts are created by and for north western nations and are quite difficult to imitate in Indian cities because of challenges like large slum areas, low open public spaces, different ecology usage patterns, etc. So, options that remain for our cities is to remove encroachments from natural landscapes, replace outdated drainage system with better models, and carry out desilting and inspection of such networks as regularly as the citizens pay their taxes.

Floods in Cities

In 2014, China launched the popular initiative called the Sponge city. On similar lines, city of Vinh in Vietnam also adopted ‘city as sponge’ strategy to lessen the impact of seasonal floods on vulnerable urban areas. In China, more than 30 cities currently are part of the initiative wherein 80 per cent of all urban land is enabled to absorb or reuse 70 per cent of storm-water. It was only this year in July that Municipal Corporation of Chennai had announced its decision to transform 50 parks into ‘sponge parks’ in the city to store rainwater run –off; but no other Indian city has considered this method so far.
Flood menace of Mumbai is infamous. In June 2020, Iqbal Singh Chahal, the then Commissioner of Brihanmumbai Municipal corporation had claimed that the city was all set to meet the rains with its over 2900 km long storm water drain network, which had been desilted and cleaned up by the Corporation. However, in August that year, the city flooded nonetheless, including areas in south Mumbai which had never flooded before. Stalin D, Director of Vanashakti had stated that recently started work on grey infrastructure, such as the coastal road project and Metro Phase – III in the region was the man-made reason behind flooding, which destroyed its natural drainage system. Unfortunately, the outdated mentality of ‘pave, pipe, and pump’ in urban development is followed by planners’ and decision makers’.
Other Indian cities including New Delhi, Pune, and Hyderabad are not doing any better either. The way these cities crumble after even a single heavy downpour, like it happened in Pune in 2019, in Hyderabad in 2020, and in Chennai in 2021, reflects on the cities’ failure to integrate the concept of sustainability in navigating the development and evolution of urban areas. However, urban floods of this scale cannot be contained by the municipal authorities alone. Nor can they be dealt with by the state governments. They cannot be managed without concerted and focused investment of energy and resources. Such investments can only be done in a mission mode method with active participation of civil society organisations at the metropolitan scale.

Increasing instances and loss

It is the warming global temperature that not only causes rise in sea level, but also creates possibility of increasing intensity and frequency of heavy downpours, which means increased number of localised and riverine flooding. In 2021, a total of 432 catastrophic events were recorded around the world, wherein 223 events were that of flood, according to reliefweb. An assessment of its database noted that an average of 163 annual flood occurrences were recorded across the 2001-2020 period, indicating a major rise in flood occurrences.
The table collaborated from the Emergency Events Database (EM-DAT) highlights that no real progress has been made by the nation so far in mitigating floods, because economic impact of flood events in India has only been increasing (see table 2). The United States Trade and Development Agency (USTDA) had estimated losses worth `14,000 crore caused by flooding in Mumbai between 2005 and 2015.
The city authorities of Shanghai, which has already adapted the sponge city initiative, have been putting enormous stock in adaptation strategies because the city is expected to experience rainfall and flooding that will be 20 per cent higher than the global average by 2050. Other flood-prone cities like Rotterdam (Netherlands) and Fukoka (Japan) have introduced waterproofing measures and green stormwater infrastructure and increased urban green space in preparation of floods. Meanwhile, the approach of dealing with floods in our nation still largely remains about managing the flood water once it has started submerging a city, rather than developing structures and mechanisms in advance to deal with the possible flooding of an area or a city. Whilst, it is not necessary that same mechanisms will work for Indian urban spaces, there is a need to put more serious efforts in addressing this issue.

Grey v/s Green

In an interview with the Team Urban Update, Mundoli stated that the key in mitigation of urban floods will be to remove encroachments from the important natural landscapes, such as those around the coastlines. She added that people have turned blind in the name of ‘urban development’, which has led to and continues to lead to unwarranted deforestation, covering up of natural landscape with impervious surfaces, thereby further reducing natural mechanisms that could have been useful in managing excess water from floods. “Now it is no longer a matter of thinking ahead or preparing for future catastrophes; frequency and intensity of rainfalls across our cities, especially those on coast has already become pretty regular in comparison to the earlier patterns, therefore, now the question for the decision makers and people is whether they will choose grey infrastructure or save the city,” she added.

The city authorities of Shanghai, which has already adapted the sponge city initiative, have been putting enormous stock in adaptation strategies because the city is expected to experience rainfall and flooding that is 20 per cent higher than the global average by 2050. Meanwhile, the approach of dealing with floods in our nation still largely remains about managing the flood water once it has started submerging a city, rather than developing structures and mechanisms in advance to deal with the possible flooding of an area or a city