Mumbai has lost 81 per cent of open land, 40 per cent green cover and nearly 30 per cent of its water bodies between 1991 and 2018 while the built-up area has increased by 66 per cent during the same period, a recent study has found.
This loss of open land (barren spaces without any vegetation), green cover (forests and scrublands) and water bodies (lakes, ponds, floodplains) had led to the financial capital witnessing a two degree Celsius average temperature rise across 27 years, the study found out.
“With this pace of urbanisation and landscape transformation, it is expected that the Urban Heat Island intensity will further increase in the coastal city,” researchers from Faculty of Natural Sciences, Jamia Millia Islamia in New Delhi, Osmania University, Hyderabad, and Aligarh Muslim University, Uttar Pradesh, documented in their study ‘Urban Heat Island Dynamics in Response to Land Use/Land Cover Change in the Coastal City of Mumbai’, published in the peer reviewed ‘Springer Journal of the Indian Society of Remote Sensing’.
The extreme heat that one experiences when strolling through any urban landscape is caused by the Urban Heat Island effect, a micro-climatic phenomenon. This is due to a number of causes, the most prominent being the usage of materials such as concrete, said Atiqur Rahman from the Department of Geography, Faculty of Natural Sciences, Jamia Millia Islamia.
“This will not only deteriorate the urban thermal environment but also increase the serious risks to health for city dwellers,” Rahman said, adding, “This rise in heat intensity in Mumbai is linked to the declining green cover in the city which is the result of the large-scale transformation of green cover into built-up land for the infrastructural development in the city.”
Using satellite imagery (USA-NASA Landsat datasets freely available), the authors studied an area of 603 square km of Mumbai region (both city and suburbs) to understand the land-use and land-cover changes, difference in maximum, minimum and average temperatures (for Urban Heat Island intensity), land surface temperatures, changes in vegetation cover versus urban built-up density between 1991 and 2018.
Shahfahad, Senior Research Fellow at the Department of Geography, Jamia Millia Islamia, and the lead author of the study, said, “We found that rapid uncontrolled urbanisation over the past five to 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 the city’s built-up surfaces.”
The study noted that during 1991-2018, Mumbai lost nearly 40 per cent of its green cover, including forests (dense vegetation) and scrubland (sparse vegetation) that fell from 287.76 square km in 1991 to 193.35 square km in 2018.
The area of open land fell by more than half from 80.57 square km in 1991 to 33.7 square km in 2018. Mumbai also saw reduction in water bodies from 27.19 square km to 20.31 square km during the same period.
Meanwhile, the conversion of open lands, green cover and water bodies to buildable land showed an increase from 173.09 square km in 1991, which nearly doubled and reached 346.02 square km in 2018.
“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.
Citing the recommendation of the World Health Organization (WHO), which has set a minimum limit of per capita green space in urban areas as nine square metre for a healthy living, the authors suggested, “To overcome the heat stress there is an urgent need to promote urban greening at micro/wards/mohalla level and rooftop terrace gardening as well as discouraging the use of glasses in the high-rise buildings etc.”