Satellite Images Show How Cities Are Heating Up
Chennai: Between 2003 and 2020, India's cities warmed at 0.53°C per decade—double the rate of the rest of the country. Satellite imagery reveals this transformation, documenting how green turned to grey, water bodies vanished, and land surface temperatures soared—in some cases by as much as 15°C in three decades. This was particularly pronounced in the northwestern, northeastern and southern regions. We looked at studies that analysed data from nine cities spanning up to five decades. The images reveal three patterns: extreme sprawl that replaced natural landscapes with concrete, the paradox of the city that added trees but still got hotter, and the systematic loss of water bodies that once cooled urban environments. As cities turn into heat islands, India’s urban population exposed to high temperatures is estimated to rise eightfold by 2050, as IndiaSpend reported in the first part of this series. Vulnerable communities, unable to afford cooling, will suffer the most. “This inevitable development could exacerbate the Urban Heat Island crisis our cities are already facing and further reduce the quality of living," says Abhiyant Tiwari, climate resilience lead and health consultant at the Natural Resources Defense Council. Every city shows increased built-up area and rising land surface temperatures. But the details vary. Bengaluru experienced the most extreme sprawl and temperature rise. Hyderabad presents a paradox—green cover increased 197%, yet LST rose 7.55°C. These variations reflect different urbanisation drivers: Bengaluru's tech boom, Hyderabad's IT and pharmaceuticals, Patna's administrative role, Chennai's haphazard expansion. Extreme sprawl In Bengaluru, built-up area rose ten-fold from about 6,000 hectare in 1973 to 64,000 hectare in 2023, accompanied by a fall in area of vegetation cover (88%) and water bodies (79%) from 69,000 hectare to 9,900 hectare, researchers at the Indian Institute of Science have found. Just in the last three decades, this urban sprawl has caused the overall average LST in Bengaluru to rise by 15.13°C, according to a study by researchers at the city’s Christ University and Qatar University. From a climate and public health standpoint, this increase would be classified as “severe and hazardous”, says Shikha Patel, lead author and research assistant at the Department of Architecture and Urban Planning in Qatar University. This rate of increase is not acceptable, she adds, and indicates an urgent need for cooling strategies. Patel points to the rapid population growth, economic development, and the city's emergence as a major IT and industrial centre as primary factors. The most intense phase of urban sprawl and land use change, as evidenced by satellite images, occurred after the early 2000s leading to the creation of urban heat islands, she adds. In the case of Vijayawada, which saw a 15.84°C rise in LST between 2001 and 2023, the built-up area grew 58%, while the extent of water bodies fell 38% and vegetation declined 42%. “Vijayawada follows a fan-shaped, unidirectional growth trajectory. Bounded by hills to the east and west and the Krishna river to the south, the city’s expansion has been predominantly oriented towards the northeast,” explains V. Vinoj, associate professor at the School of Earth, Ocean and Climate Sciences, IIT Bhubaneswar. Its location as a transportation hub, and recently, the proximity to the new state capital Amaravati contributed to rapid urban growth. “The older core city region situated near the river exhibits the highest land surface temperatures (LST), highlighting the urban heat concentration in this area,” he adds. In Patna, which saw a 4.5°C rise in LST, the built-up area doubled between 1988 and 2022—most of it after 2005. During this period, the extent of water bodies reduced by 34% and vegetation by 84%. The city demonstrates a concentric growth model, marked by the city’s radial outward expansion, Vinoj says. Patna functions as the administrative hub while also serving as a major hub for healthcare and education. This role, coupled with significant rural-to-urban migration, continues to shape the city’s urbanisation dynamics, he explains. Green cover paradox In Hyderabad, the urban heat island phenomenon is stronger at night. The city is 0.7°C cooler than its peripheries and peri urban areas during the day and 1.9°C warmer at night, according to a 2024 review by the Centre for Science and Environment. In two decades to 2023, its built-up area doubled, but green cover also rose from 9% to 27%. This in turn has moderated daytime temperatures, the review says, but widespread concretisation still reduces thermal comfort at night. Experts say that the IT boom and the bio-pharmaceuticals industry in Hyderabad have been the main reasons for the increase in population. "Green cover definitely has increased in Hyderabad due to consistent efforts through the Haritha Haram programme. But this does not offset the UHI crisis or significantly reduce temperatures," says D. Sabarinath, a geographer and urban researcher. "This is largely because forest cover is lost due to rapid urbanisation and this can't be replaced by scattered planting without planning. For example, they grow eucalyptus trees because they mature fast but the capability of evapotranspiration for this species is low. So data shows tree cover has increased but on ground, unscientific tree planting can reduce aquifer levels and cause more damage," he adds.