It was an unusual display of emotion for normally stoic Mumbaikars, who braved arrests on Friday night to try and stop the cutting of nearly 3,000 trees in Aarey Colony, known as the Indian city's "green lung". On Monday, the Supreme Court, after hearing a petition, stayed the cutting of more trees until Oct 21. As rising heat and frequent floods batter some of the world's most densely populated and polluted cities in India, urban residents are rallying around fast disappearing green spaces seen as vital safeguards. In the southern city of Bengaluru, residents protested the cutting of hundreds of trees for a flyover, while a petition led the Supreme Court to slam the amendment of a colonial-era law to open up the Aravalli mountains for real estate development. "Earlier, villages bore the brunt of climate-change impacts, but now cities are also experiencing flooding, air pollution and water scarcity more often," said Kanchi Kohli, a researcher at the Centre for Policy Research think tank in Delhi. "People have realised that disappearing green spaces are a part of the problem, and there is a strong determination to fight on the streets and in the courts because they see no other way to make themselves heard," she said. With almost 70% of the world's population estimated to be living in cities by 2050, mainly in Africa and Asia, cities will bear the brunt of warming temperatures, climate experts warn. Asia's booming cities are losing green spaces as a construction boom gobbles up land for offices and apartments, worsening the heat island effect and causing flooding that has killed hundreds from Mumbai to Manila, according to environmentalists. "We're not saying, don't cut a single tree; we're only saying don't needlessly cut trees because there simply aren't enough trees," said Zoru Bathena, an activist who has filed several petitions against tree felling in Mumbai. "Why should development always be at the cost of the environment?" NET LOSS A fifth of the world's major cities will face "unknown" climate conditions by 2050, as rising temperatures heighten the risks of drought and flooding, scientists at the Crowther Lab in Switzerland have warned. Cities in tropical regions such as South Asia are likely to see some of the strongest impacts, the study showed. Nearly 300 people died in floods in 2015 in the coastal city of Chennai, where floodplains have long been built over. Mumbai's tree cover has fallen to less than 13% from more than 35% in the 1970s, according to the Indian Institute of Science, which recommends green cover of a third of total area. Indian Prime Minister Narendra Modi has pledged to restore 26 million hectares of degraded land by 2030 through tree planting and other means, alongside a push to switch to electric vehicles by 2030 to cut carbon emissions. But the loss of green spaces in urban areas cannot be offset by planting trees elsewhere, said Chetan Agarwal, an analyst at the Centre for Ecology, Development and Research. "The loss of green spaces in cities represents a net ecological loss, as large numbers of people are concentrated there and are deprived of their benefits," he said. "Small and large green spaces provide a toehold for nature in the city, with manifold benefits including better air quality and overall health," he told the Thomson Reuters Foundation. From Athens to Seoul, big cities worldwide are planting more trees to minimise the severity of heatwaves and floods, and to boost people's physical and mental health. The United Nations recently unveiled plans to create urban forests in cities in Africa and Asia to improve air quality, cut the risk of floods and heatwaves, and halt land degradation. DUST STORMS Nearly 30% of India's land area has been degraded through deforestation, over-cultivation and depletion of wetlands, according to the government. This is evident in the Aravalli mountains, which run through four states for a distance of nearly 700km (435 miles). Dilution of environmental laws over the years have led to deforestation, construction and illegal mining, causing desertification, drying up of lakes, and more frequent dust storms. The Delhi Ridge, a stretch of the Aravallis, acts as lungs for the city's toxic smog, and is a cherished green space. In February, Haryana state amended the Punjab Land Preservation Act of 1900 to open up thousands of acres of forest land in the Aravallis for construction and mining, sparking protests in Delhi and in neighbouring Gurugram. Days later, the Supreme Court, responding to a petition by environmentalists, said it was "shocking" that the Haryana government was destroying the forest, and that the new law cannot be enforced without the court's permission. "The loss of the Aravallis will impact water security, fragment wildlife habitat and corridors, and reduce the capacity to mitigate air pollution in Delhi and elsewhere," said Agarwal. But as urban populations expand rapidly, land is needed for housing and transport, authorities say, putting pressure on green spaces including cemeteries. "We do not wish to cut even a single tree in Aarey, but development is also important. We will plant more trees in place of those cut," said Devendra Fadnavis, chief minister of Maharashtra state where Mumbai is located. The densely wooded area, spread over 16 sq km (6 sq miles), is home to 27 tribal villages and various animal species, including leopards. Over the past few decades, swathes of land have been allocated for slum resettlement, a defence training unit and a zoo. The site for the metro shed is a 33-hectare plot. "We're not against the metro; we all want better public transport. But this is just a shed - it can be built elsewhere without cutting so many trees," said Bathena. Commitments to increasing forest cover and cutting carbon emissions are not enough, said Kohli. "Building a flyover, or a metro shed by cutting down trees can get us more convenience, but at what cost?" "We have to ask whose desires dominate, and if this is the sustainable urban vision we want," she said.