How 'sponge' cities can deal with floods

Updated 6:00 AM ET, Tue April 12, 2022
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As climate change brings more extreme weather events, cities need to be prepared to combat floods. Global global built environment consultancy Arup recently published a "Global Sponge Cities Snapshot" report that surveyed seven cities on their natural ability to manage heavy rainfall. A "sponginess" ranking from 1% to 100% was calculated based on the quantity of green spaces, the quality of soils and the water run-off potential. Auckland, New Zealand (pictured) came top in the rankings. Fiona Goodall/Getty Images
Auckland scored 35% on its overall "sponginess." Home to 1.4 million people, the city has many large gardens and parks including Mount Eden, the site of a dormant volcano. The city's stormwater management initiatives include systems to collect and slow the release of rainwater, defending the city from heavy rainfall and storm events. imageBROKER/Shutterstock
Nairobi, the Kenyan capital, also known as "the Green City in the Sun," is 34% spongy and ranked second out of the seven cities. Nairobi National Park (pictured) and other large grasslands can be found next to the city's built-up areas. According to Thomas Sagris, Arup's global water research lead, grasslands are better at absorbing rainwater than trees because they soak up water immediately. Khalil Senosi/AP
In contrast, the slums of Nairobi such as Kibera (pictured) are densely populated, with little to no greenery. These areas are particularly vulnerable to floods which affect the livelihoods and safety of the residents. In May 2021, severe floods caused by heavy rainfall led to casualties and many people living near the Mutuine River were displaced. Donwilson Odhiambo/SOPA Images/Shutterstock
In joint third place alongside Mumbai and Singapore, New York City scored 30% for its "sponginess" because it has absorbent soils that minimize water runoff. According to the report, there are plenty of parks and green areas in the Bronx, located to the north of the city. However, aside from Central Park (pictured), the south of the city has a lower distribution of trees and greenery with a higher volume of urban developments.
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As well as increasing the ability of cities to manage rainfall, green infrastructure can bring additional benefits to bolster resilience against the impact of climate change. Having large areas of tree coverage -- like in Mumbai, in India -- can shelter the city from the urban heat island effect, a phenomenon that occurs when heat is absorbed by pavements and buildings. Dinodia Photo/Corbis Documentary RF/Getty Images
To improve the overall "sponginess" of a city, the key is to integrate green infrastructure in existing building developments, according to the report. For over 50 years, Singapore has worked to incorporate trees and plants on roads and highways. Frequent rainstorms during wet months have also prompted the island to develop an efficient drainage system to lower the risk of floods. Therin-Weise/picture-alliance/dpa/AP
According to the report, climate change could displace millions of people from the coastal Chinese megacity of Shanghai (pictured). Home to more than 28 million people, many of whom live in high-rise buildings, Shanghai has a 28% "sponginess" score. It is part of China's sponge city initiative, launched in 2014, which aims to make 80% of the country's urban areas "spongier" with green infrastructure by 2030. Hector Retamal/AFP/Getty Images
London (pictured), which came last for overall "sponginess," at 22%, experienced severe floods in July 2021. Despite having a good spread of urban parks across the city, the lack of tree cover and less-absorbent clay-rich soil contributed to the low score. According to an IPCC report released last year, the risk of river flooding in Europe will also increase significantly as the climate warms. Justin Tallis/AFP/Getty Images