A recent study published in npj Urban Sustainability—titled “Surface Urban Heat Island Effects Intensify More Rapidly in Lower Income Countries” (Yuan et al., 2025)—has rattled many urban professionals out of academic detachment. It’s one thing to understand urban heat islands (UHIs) as a technical phenomenon. It’s quite another to confront how unjustly this burden is distributed worldwide.

The data is both vast and precise: 4.8 million urban grids tracked from 2003 to 2018 reveal a global average urban heat island (UHI) rise of 0.021°C per year. But the median health story is different for residents of lower-income countries. Twenty-seven per cent of urban areas in these nations show sharp daytime heat increases. At night, heat lingers hardest in lower-middle-income countries, where infrastructure is thin and adaptation tools are scarce (Yuan et al., 2025).

These numbers aren’t just statistics; they are warnings wrapped in data.

The Uneven Heat Map

In India’s rapidly urbanising regions—where growth is both a promise and a pressure cooker—this global picture mirrors on-the-ground reality. Cities in lower-income regions are urbanising fast but often without the environmental buffers—trees, reflective surfaces, and smart zoning—that richer cities rely on.

While high-income countries like the US and Japan also experience rising UHIs, they simultaneously record decreasing heat in areas benefiting from deliberate planning, policy enforcement, and green infrastructure. In contrast, low-income countries face near-total heat rise with few mitigating zones—an urban thermal siege.

This is not surprising. Earlier research by Giridharan & Emmanuel (2018) noted how compact urban form in tropical cities increases thermal discomfort and cooling energy demand by 15–25%, especially in areas with low vegetation or inadequate ventilation pathways.

From Planning to Pain

What’s most alarming isn’t the heat itself but the lack of capacity to manage it. The study draws a direct link between rising SUHII and the quality of governance, infrastructure, and economic resilience. Cities with high quality-of-life scores like Dublin are holding their own with green parks, energy-efficient housing retrofits, and climate-responsive planning.

In contrast, Brazzaville in the Republic of Congo lost over 50% of its green cover between 2002 and 2022, with temperatures now soaring above safe thresholds. The city lacks both the resources and planning systems to respond. The gap between cities with agency and those without is deeply unsettling. It aligns with findings by Li et al. (2019) showing that urban heat significantly raises cooling demand and energy costs, particularly in poorer cities lacking insulation and adaptive infrastructure.

Heat and Energy: A Wicked Feedback Loop

The feedback loop between heat and energy demand further complicates matters. As cities heat up, residents increasingly rely on air conditioners—if they can afford them. This leads to more waste heat and emissions, further raising urban temperatures. It’s a vicious cycle that poorer cities can neither afford to enter nor to escape.

A review by Hashemi & Mills (2025) in Energy & Buildings highlights that UHIs can raise cooling energy demand by up to 65%, depending on urban layout and materials. Yet most energy models omit UHI in their calculations. This oversight means future cities are designed on incomplete data, pretending the urban microclimate doesn’t exist. The consequences are real: building codes and designs remain outdated and disconnected from the new heat reality.

Lessons from Hong Kong: Urban Form Matters

A recent study by Wu et al. (2023) in Sustainability explored how urban environmental characteristics influenced land surface temperatures in Hong Kong between 2017 and 2022. The findings are stark: annual land surface temperature rose from 21.13°C to 23.46°C. Built-up areas accounted for 53.4% of elevated temperatures, while vegetation and water bodies had a cooling effect. Urban form matters.

What Needs to Be Done

India is urbanising at breakneck speed. Cities like Delhi, Mumbai, Bengaluru, and Hyderabad are already grappling with severe UHIs. The heat is not just an environmental discomfort—it’s a crisis for public health, productivity, and infrastructure. Experts recommend:

1. Prioritise green infrastructure: Expand urban forests, green belts, and shaded streets; scale up Miyawaki forests and green roof programs.
2. Integrate UHI data into smart city planning: Include temperature-sensitive zones and heat maps in municipal dashboards.
3. Retrofit buildings: Incorporate passive cooling techniques and reflective materials in both new and existing buildings, especially low-income housing.
4. Regulate urban sprawl: Urban expansion should include mandatory green coverage and thorough environmental impact assessments.
5. Invest in public awareness: Educate citizens on maintaining green balconies, using light-coloured paint, and carpooling to reduce urban heat.
6. Build local data systems: Many vulnerable cities lack granular climate monitoring, essential for effective planning and funding.

If India does not act swiftly, its cities could become some of the hottest and most unequal places on the planet.

Final Reflections

Reading this study alongside others like Hong et al. (2023) and Singh & Sharston (2022) reinforces a sobering reality:

“The urban heat island is not just a climate phenomenon—it’s a structural inequality. Some cities have shade and strategy. Others have asphalt and anxiety.”

Unless action is taken urgently and globally, the gap will widen—not just in degrees Celsius, but in lives lost, livelihoods threatened, and futures foreclosed. The message is clear: waiting for the next dataset is no longer an option.