Mumbai lost 23% of green cover in millennium’s 1st decade

Mumbai lost 22.6% of its green cover in the decade spanning 2001-2011, with losses crossing 60% in parts of the western suburbs, according to a new study from IIT Bombay. Some neighbourhoods “witnessed extreme levels of ungreening”, the study said.

Sixty-eight of the city’s 88 census wards lost green cover in 2001-2011, found doctoral student V Sathyakumar and professors R.A.A.J. Ramsankaran and Ronta Bardhan, who analysed satellite imagery along with census data to map neighbourhood-level shifts in green cover. Per capita greenery also reduced by a median of 2.8 square metres per person, they found. The decline was not only in quantity, but also quality: most neighbourhoods saw fragmentation of their green spaces.

The high losses in the western suburbs reflect the pace of commercial and residential development in the 2000s, said Sathyakumar. These areas are also relatively verdant, he notes, with its proximity to mangroves, the forested Aarey Colony, and Sanjay Gandhi National Park.

The worst hit were: Goregaon, which had 62.5% of green space in 2001, but only 17.4% in 2011; Andheri (West), where the percent of green space fell from 63% to 20%; and Malad (West), which went from 62% of green space in 2001 to 19.5% in 2011.

Kandivli and Vile Parle saw similarly steep falls in green cover, while eastern suburbs like Mulund and Ghatkopar also saw significant declines.

By contrast, the historically densely-populated island city saw smaller reductions in green cover in the same period—Dadar, Sion, and Matunga even saw gains—but also did not have as much green cover to begin with, researchers noted. (In this study, green cover refers to any kind of vegetation, whether trees, roadside shrubs, or parks.) “These findings show the need for targeted greening programmes for different neighbourhoods, specifically to develop more spaces in the island city and conserve and improve those in the suburbs,” said Ramsankaran, an associate professor of civil engineering at IIT Bombay.

Fragmentation emerged as a key issue. In most parts of the city, the mean area or size of green space shrank in that decade—the median decrease was 3.21 hectares—while the number of patches per square kilometre increased. Distance between green spaces also fell.

Taken together, said researchers, these findings indicate that larger green spaces splintered into smaller ones. The trend was especially intense in suburban areas like Andheri (West), Jogeshwari (West), Goregaon, and Malad (West), where satellite imagery showed “large and aggregated green space patches had turned into isolated single-pixel patches”.

Fragmentation indicates deterioration of ecological quality, said Bardhan, who is a lecturer on sustainability of built environment at Cambridge University. “Contiguous green spaces support more biodiversity, provide a larger habitat, and facilitate species dispersal,” she said. “Further, fragmentation makes green spaces more vulnerable to the ‘un-greening’ phenomenon.”

Although a few areas in the island city saw per capita green cover rise—in Walkeshwar, for instance—these areas were also depopulating in that period. “Wherever per capita green cover went up, it is primarily because of population decrease,” said Sathyakumar. “But where it went down, it is mainly due to decrease in green space, not population increase.”

Indeed, 23 census wards saw a reduction in per capita green cover despite a decline in inhabitants. In 2011, only 47 census wards had more than 9 square metres of green cover per person—an often cited standard compared to 56 census sections in 2001.

Surprisingly, some island city neighbourhoods like Matunga, Dadar, and Sion saw increases in green cover. Researchers attributed the improvement in these areas to increased greening along roads and railway lines and the emergence of small green patches in a few residential pockets, as well as relatively stable traditional green spaces. Matunga also a saw a decline in population, Bardhan noted.

However, further investigation of these areas is needed, researchers said. In addition, the green cover scenario in the island city areas may have changed in recent years as redevelopment stepped up.

Researchers hope their work will help with urban green-space planning. “Traditionally urban green space standards focus only on quantity, specifically green space per inhabitant,” added Bardhan. “Yet, these standards do not reckon the level of fragmentation or accessibility, which have overarching influences on the benefits received by urban dwellers.”

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