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Consultancy Arcadis' Sustainable Cities Index, published on Monday, ranked 50 of the world's most prominent cities by looking at their environmental progress, viability as a place to live and financial stability.
"Frankfurt's high ranking in the Sustainable Cities Index may come as a surprise, however, the self-proclaimed 'Green City Frankfurt' has a long track record of proactively taking action to improve its sustainability," Arcadis said.
The index takes into account 20 different indicators ranging from greenspace to income inequality to ease of doing business.
Arcadis defines a sustainable city as one that "works well for their citizens in the present without causing problems for themselves and the rest of the world in the future."
Roughly half of Frankfurt's surface area is "green", according to the city's environment department, which notes that 52 percent of the city area has been set aside for recreation and to offset climate change. It consists of parks, woodland, farmland, orchard meadows, grassland, allotments and hobby gardens, cemeteries, roadside grass verges and bodies of water.
Frankfurt is also a founding member of the Climate Alliance of European Cities, pledging to continuously reduce its carbon emissions by 10 percent every five years, resulting in a 50 percent cut by 2030.
European cities dominated the top ten, with London and Copenhagen following in second and third place, respectively, and Amsterdam and Rotterdam in the fourth and fifth spot.
"London scores highly in part due to good health outcomes and excellent higher education facilities, alongside being the best-connected global city, with New York, in terms of its importance to global business networks," Arcadis said.
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Rounding out the top 10 were Berlin, Seoul, Hong Kong, Madrid and Singapore, in sixth to tenth place, respectively.
"Whilst Singapore is placed in the top ten in the Sustainable Cities Index, it ranks lower than Hong Kong and Seoul largely due to lower scores for indicators like work-life balance, having expensive property prices, low use of renewable energy and a high cost of doing business," Arcadis said
However, the city-state performs very well from an environmental perspective, demonstrating a commitment to green urbanization, it noted.
Interestingly, some of the fastest growing cities in Asia were the least sustainable including Jakarta (45th), Manila (46th), Mumbai (47th), Wuhan (48th) and New Delhi (49th).
"The prevalence of such rapidly growing cities amongst the bottom ten highlights the ground that many of these emerging cities still have to cover."
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