Mumbai saw 99.9% increase in built-up area in 27 years, reveals study

A recent study, published in the peer-reviewed Springer Journal of the Indian Society of Remote Sensing, found that between 1991 and 2018, Mumbai saw a corresponding increase of 99.9% in its built-up area

A recent study, published in the peer-reviewed Springer Journal of the Indian Society of Remote Sensing, found that Mumbai lost 58.17% of its open spaces, 40% of its green cover and about 25.30% of water bodies between 1991 and 2018. During these 27 years, the city saw a corresponding increase of 99.9% in its built-up area.

A recent study, published in the peer-reviewed Springer Journal of the Indian Society of Remote Sensing, found that Mumbai lost 58.17% of its open spaces, 40% of its green cover and about 25.30% of water bodies between 1991 and 2018. During these 27 years, the city saw a corresponding increase of 99.9% in its built-up area. (REUTERS)

The study also demonstrates correlation between increase in built-up area and a rise in micro-climactic “urban heat island’ phenomena. Over 27 years, researchers have noted, Mumbai’s average temperature has increased by a worrying two degrees celsius.

The study (’Urban Heat Island Dynamics in Response to Land-Use/Land-Cover Change in the Coastal City of Mumbai’) was conducted by researchers from the Faculty of Natural Sciences at Delh’s Jamia Millia Islamia University in New Delhi, Osmania University in Hyderabad, and Aligarh Muslim University, Uttar Pradesh.

Researchers used NASA landsat datasets and imagery to study changes in land-use, land-cover and land surface temperatures over 603 sq kms of Mumbai city and suburbs.

Shahfahad, a senior research fellow at JMU and lead author of the study, said, “We found that rapid uncontrolled urbanisation over the past five-six decades attracted a large population by providing better economic opportunities. As a result, natural land use patterns such as vegetation cover, scrublands, wetlands, and open lands have all been transformed on a large scale into built form.”

The area of open land fell by more than half from 80.57 sq. km in 1991 to 33.7 sq. km in 2018. Mumbai also saw reduction in water bodies from 27.19 sq. km to 20.31 sq. km during the same period. Conversely — due to conversion of open lands, green cover and water bodies — the extent of built-up area nearly doubled from 173.09 sq km in 1991 to 346.02 sq. km in 2018.

These transformations were found to radically alter land surface temperature dynamics, leading to more intense urban heat island formation. “We observed that the average temperature in 1991 was 34.08 degrees Celsius. It rose to 36.28 degree Celsius in 2018 (a 2.2-degree Celsius increase) under the heat island zones (vulnerable areas), thus exposing people to higher heat risk,” said Shahfahad.

Roshni Udyavar Yehuda, president, Institute of Environmental Architecture and Research, who was not involved with the study, said, “The urban heat island effect is caused due to increase in hardscapes such as building materials including concrete, steel and glass, both on the buildings and on streetscapes or open spaces.” “Curtailment of wind flow which often occurs in urban areas due to closely built vertical structures is also a problem,” she explained, emphasising that such micro-climactic changes must be clearly reflected (and prepared for) in Mumbai’s official development plan.

Other experts, too, expressed concern over these findings, which disproportionately affect disadvantaged communities. “The urban heat island effect and population density have a strong association. In Dharavi, the urban poor suffer the most since they can’t afford houses or air conditioners. Those living in high rises or gated communities, on the other hand, may not be as badly affected as they have access to air conditioners and means to reduce heat exposure,” said Akshay Deoras, a meteorologist with the University of Reading, UK.

Deoras also clarified that the worst affected are those who must commute long distances to work (as is common in Mumbai) as well as those working outdoors.

The associated impact on urban heat owing to an increase in built-up area, he explained, may not even affect residents of the area but labourers, small-shop owners, and domestic help.