Creating sponge cities

The impact of climate change has been discussed at various platforms since the United Nation's first environment conference held at Stockholm, Sweden in 1972. Recently in Paris, the adversities associated with the global climate change were reverberated by various nation heads. One of the consequences of climate change experienced globally is urban flooding. Frequent urban flooding is a critical challenge faced by cities and towns as an outcome of anthropogenic factors and resultant climate change. Urban areas located by the seas, on the banks of the rivers and other water bodies are the ones facing the worst impact of urbanisation and encroachments in the name of development. It is known that due to the dense population and development activities in urban areas, the impact of the flood experienced is multiple times in the urban areas than the rural areas. Urban flooding causes multiple direct and indirect losses in terms of lost human lives, health challenges, physical damages to the infrastructure and other assets. It also hampers the economic activities by disrupting transportation and networks.

Every year, June to September, the south-west monsoon floods the streets of many important and big cities like Mumbai, Bangalore, Delhi, Hyderabad, Gurugram, and Ahmedabad along with many others. In 2015, the monsoon during its retrieval wreaked havoc on the city of Chennai and brought life to a standstill. Not much has changed since then, with the floods in Kerala being notable evidence. The preparedness of cities against any future natural disaster remains a serious concern as disaster management plans are half-heartedly implemented. It has been experienced invariably that heavy rainfall for even a short duration clogs the pipes and drainage systems of the cities, causing the water-logging. Concrete pavements further prevent the water to seep in, resulting into flood like situations.

The concept of sponge city

Rampant urbanisation has led to a depletion of forests. The growth of towns and cities without implementing a sustainable town planning and management principles has pushed nature to an ecological imbalance. The rapid encroachment of wetlands, low lying river banks and lakes in the cities amplify the aftermath of natural disasters like a flood. Rainstorm runoff in the urban area is magnified by the clogged drainage and unsustainable construction activities. Many countries across the globe like USA, China, Germany, and New Zealand have begun to undertake Low Impact Development models of urbanisation that incorporate sustainable and unconventional water management practices. In 2013, China introduced the concept of 'Sponge City' that is based on a six-word pillar - infiltrate, detain, store, cleanse, use, and drain. It seeks to develop new cities like Nanhui New City (also known as Lingang) and also retrofit the water management system in old ones like Shanghai. The cities are to be designed in a manner that will absorb maximum rainfall (up to 70 per cent), clean and utilise it to attenuate the rainstorm runoff and its subsequent impacts. This incorporates rainwater harvesting strategy, building permeable roads, green and blue infrastructure such as low carbon buildings, rooftop gardens, wetlands, ponds, lakes and marshy depressions called swales. Sponge city project is already extended to 30 cities in China.

Rummelsburg and other neighbourhoods across Berlin have implemented the sponge city concept that utilises the stormwater by not just piping it away into the sewer or the drainage system, but retaining and replenishing the groundwater level. The roof gardens and swales in the cities absorb the runoff water, reduce the surface water pollution and recharge the groundwater. The roof plants and marshy wetlands that absorb the water also cause a cooling effect through evaporation during summers. Chicago is another example where projects like 'Green Alleys, which focus on increasing the permeable pathways, have taken off. Many other water management projects have been adopted by the cities across the USA to fight against urban sprawling.

Lessons for India

Across the globe, countries are adapting to climate change by adopting innovative and sustainable water conservation measures. It is vital that the state governments in collaboration with the local municipalities undertake innovative approach to tackle the outcome of the growing urbanisation in its cities. In its global assessment survey, the UN projected that the population in India would be living under severe water stress by 2050. NITI Aayog, in its Composite Water Management Index Report, talked about the water crisis in the country. As per the report, India is suffering from the worst water crisis in its history and around 600 million Indians face some form of water stress. Many cities like Delhi, Bengaluru, Chennai, and Hyderabad are going to run out of the groundwater by 2020. In contrast, it is also evident that many of these towns and cities face problems of urban flooding every year due to heavy rainfall. We need to channelise this excess rainfall into a water storage system so that situation of water crisis can be dealt with. The cost of such development seems high but is not much when compared with the direct and indirect damages brought upon the cities by urban flooding.

Retain, revive, and restrain are the keys to water conservation and sustainable town planning. man-made structures, unlike natural systems, are not built to retain water, therefore, we need to refurbish the existing infrastructure around us to prevent or at least mitigate the impact of flooding. Our fight against urban flooding must envisage a sound and a sustainable rainstorm management plan. The new developments based on the principles of a Sponge City would be capable to handle the disastrous outcomes of the stormwater. The existing infrastructure is to be refurbished on the blueprint of a sponge city to accommodate the consequences of torrential rainfalls and surface runoffs. During rainstorms, Sponge City design would act as a defence mechanism supporting greater absorption and water retention. It is also essential that we revive the existing water bodies like wetlands, lakes, and ponds in our cities and restrain construction and encroachments on the floodplains and low lying area. Together these measures would better equip our cities to adapt and mitigate the adversity of the climate change such as urban flooding.

(The author is Young Professional, EAC-PM, NITI Aayog, New Delhi. The views expressed are strictly personal)