‘42.5% decline in Mumbai’s urban green cover over 30 years’

The green cover lost is 12,446ha, more than the size of the Sanjay Gandhi National Park (10,300ha).

The city’s development over the past three decades has come at a cost – 42.5% decline in urban green cover, according to a study published last week in peer-reviewed journal Springer Nature.

Major affected areas that witnessed changes in dense vegetation include SGNP, Aarey Colony in Goregaon (in pic), Mulund, Bhandup, Gorai, Malad and Versova creek areas.

Of Mumbai’s total area of 63,035hectares (ha), the green cover was 29,260ha in 1988, which fell to 20,481ha in 1998, 17,331ha in 2008, and 16,814ha in 2018, which means an overall decline of 42.5% over 30 years. The green cover lost is 12,446ha, more than the size of the Sanjay Gandhi National Park (10,300ha).

Researchers from Manipal Academy, Karnataka, Delhi School of Economics, Kazi Nazrul University, Asansol, West Bengal, and East China Normal University, Shanghai, used Landsat-5 and Landsat-8 multi-temporal satellite images provided by United States Geological Survey to assess land use land cover (LULC) changes, land surface temperature (LST), proportion of vegetation, and other parameters for Mumbai during spring (March-April) over 30 years.

Researchers used Landsat-5 and Landsat-8 multi-temporal satellite images provided by United States Geological Survey to assess land use land cover (LULC) changes,proportion of vegetation (above), land surface temperature (LST) (below), and other parameters for Mumbai during spring (March-April) over 30 years.

The study identified a three-fold increase in land surface temperature (LST), which is negatively affected by loss of green spaces, as a reason for micro-climate changes in Mumbai, due to increase in built-up areas and subsequent latent heat. “LULC changes have subsequently altered the micro-climate of the city’s urban ecosystem.

Surface temperature variation and changes in rainfall distribution are a direct indicator of this,” said Selim Jahangir, corresponding author from Manipal Academy of Higher Education. “Preserving urban green spaces is extremely important in the context of climate change as they influence rainfall and temperature, and determine the micro climate of a city.”

Satellite maps indicated that 43% area under dense and 20% sparse vegetation steadily decreased from 1988 to 2018. Major affected areas that witnessed changes in dense vegetation include SGNP, Aarey Colony in Goregaon, Mulund, Bhandup, Gorai, Malad and Versova creek areas. Sparse vegetation reduction was witnessed across the central suburbs and isolated zones in south Mumbai, including Bandra, Khar, Malabar Hill, Pedder Road, Dadar, Lower Parel, Mazgaon, Colaba and Cuffe Parade, said researchers. “If the same trend continues for the next 10 years, it will not only adversely affect biodiversity, but also human health, by increasing urban heat island and air pollution,” said Jahangir.

The ratio of green spaces to total area fell from 46.7% in 1988 to 26.67% in 2018, with most significant changes observed during 1988-1998, when around 14% of green spaces had transformed due to development activities.

Areas of LST higher than 30.5 degrees Celsius dramatically increased from 5,232ha in 1988 to 14,339ha in 2018. Conversely, a drastic decline was recorded (32.28%) in green spaces having less than 25.5 degrees Celsius from 11,858ha in 1988 to 7,979ha in 2018.

“Increasing LST intensity would lead to an increase in urban heat island effect, bringing about adverse change in fundamental environmental indicators such as rise in atmospheric greenhouse gases, heat waves and air quality, and declining biodiversity,” said Jahangir.

The study called for requirement of policy implications at a location-specific level to harness the depleting green cover. “There is a need for the government to notice such changes, and bring in stringent regulation on arbitrary tree cutting for developmental projects,” said Jahangir. “Additionally, citizens can adopt green roof methods and balcony garden techniques similar to Singapore and Brisbane, Australia. This would increase the cooling effect and also improve air quality.”

Pankaj Kumar, author and assistant professor, Delhi School of Economics, said, “District authorities need to establish policy mitigation measures, encouraging social forestry, urban green belts, and declare more protected areas. Implications of this are not confined just to Mumbai, but the entire region.”

Mumbai’s tree census completed in 2018 identified 29.75 lakh trees, over 10 lakh more from 2008. “Tree census data is false as the same data is repeated every year. The findings of the latest study are a grim reminder that the city’s environment has remained largely ignored,” said activist Zoru Bhathena.

The Brihanmumbai Municipal Corporation (BMC) said they were maintaining 1044 plots, 254 gardens, 319 playgrounds and 432 recreation grounds. “Lack of space is a constraint, but tree cover has increased. Combined with Miyawaki plantation (dense mini urban forests) across 100 plots, spaces under flyovers converted into green zones, and more green buildings, the situation has improved from what it was five years ago,” said an official from BMC’s garden department.

BMC has issued notices for removal of 6,382 trees from January to July 26, 2020. In 2019, notices were issued for felling of 14,518 trees and 8,775 trees in 2018. The data was compiled from BMC advertisements by Bhathena.