Buildings & asphalt surfaces, not just climate, heating up Bengaluru, finds IISc study | Bengaluru News

Bengaluru: Bengaluru is warming up — and not just because of global climate change. A new scientific study has found that the city itself is becoming a heat trap because of the way its land is being used.This is called Urban Heat Island (UHI) effect, where temperatures inside the city are significantly higher than in nearby rural or forested areas. The reason? Concrete and asphalt surfaces absorb and store heat, while the loss of green spaces and waterbodies removes natural cooling systems.The Indian Institute of Science (IISc) study is one of the first to provide micro-level data, showing exactly how land use choices at even the smallest scales — like an individual plot or street — can affect urban temperatures. If Bengaluru wants to stay liveable in the coming decades, reversing some of these trends is not optional; it’s essential.What has changed in city?Researchers from IISc and partner institutes studied satellite images from 1973 to 2025 to map how Bengaluru’s landscape has changed over the decades. The findings are stark:■ Built-up areas have expanded by 1,078%. In 1973, just 7.9% of Bengaluru was built-up (meaning buildings, roads, and other paved areas). In 2025, this reached 87.6%.■ Vegetation cover has reduced by 88%. Parks, tree cover, and open green spaces have disappeared across large parts of the city.■ Waterbodies have shrunk by 79%. The number of lakes has fallen from 756 in 1973 to 216 in 2023. Many remaining lakes are encroached or polluted.How much hotter is the city?The researchers used satellite-based thermal data to calculate Land Surface Temperature (LST) — the temperature of the ground, buildings, and other surfaces.■ Maximum LST recorded: 48°C■ Minimum LST recorded: 29.8°C■ Average LST: 38.6°CWhat else was identified?■ 15.4 sqkm of heat hotspots: Areas that regularly record very high temperatures.■ 23.8 sqkm of heat sinks: Pockets that remain cooler, usually because of green cover or waterbodies.■ 545.3 sqkm of the city face unfavourable ecological conditions due to high temperatures and poor thermal comfort.Why is this happening?Heat islands form because of how cities are built and planned. In Bengaluru:■ Buildings, roads, and pavements absorb solar heat during the day and release it at night, keeping local temperatures high.■ Trees and lakes, which usually cool the environment through shade and evaporation, have been removed or degraded.■ The city’s flat terrain means there is little natural drainage of hot air.Detailed land use & temperature findingsThe researchers went beyond broad city-level data and looked at micro-level patterns, even analysing land use within small plots, the size of an individual housing site. Their key findings include:■ Barren land and fully urbanised areas are the hottest. Fully barren areas had an average surface temperature of 39.9°C; fully urban (concrete-heavy) ones recorded 39.7°C.■ Vegetated areas and waterbodies are the coolest, while those dominated by waterbodies having temperatures of around 31°C.■ Mixed-use areas (some vegetation, some built-up) have moderate temperatures. The more green space a plot retains, the cooler it stays.UHI impact on daily life■ Higher electricity bills (more fans & air-conditioners).■ Increased risk of heat stress and health problems, especially for the elderly and children.■ More pollution, as heat worsens air quality.■ Reduced quality of life, with fewer comfortable outdoor spaces.HOW TO IMPROVEThe IISc researchers have made specific recommendations:■ Policy suggestions— Retain at least 30% green space at the plot level. New buildings shouldn’t cover the entire plot with concrete or structures.— Create mini-forests in each city ward.— Rejuvenate lakes and prevent further encroachments.— Connect scattered tree patches to create continuous green corridors.— Promote green roofs and walls.— Use reflective building materials to reduce heat absorption.■ Planning & governance— Incorporate these findings into the upcoming Bengaluru Master Plan 2031.— Involve local communities in managing neighbourhood green spaces, parks, and lakes.— Strengthen decentralised governance as per the Nagarpalika Act, so local wards can manage their own green areas.