Extreme heat Archives

Interplay of Heat and Air Pollution: Unpacking the Science and Policy Blind Spot in India

Environmental challenges are an anticipated consequence of development, and India, as a rapidly growing economy, is no exception. An ever-expanding urban sprawl, growing energy needs, and accelerated land-use transformations have caused a range of environmental issues, some visible, and others, more insidious. Driven by these challenges, Indian cities are quickly transforming into hotspots of multiple, overlapping environmental stressors that are fuelling a public health crisis. Many cities are shrouded in layers of toxic haze in winter, and summer days bring with them an energy-sapping heat.

However, conversations around these environmental stressors in India have been unconnected – heat is discussed primarily during the summer, while air pollution gets a focus mostly during the winter – with their interplay largely ignored. While growing evidence has been pointing towards the synergistic effects of exposure to heat and air pollution, the science explaining how heatwaves and air pollution interact – a relationship where one amplifies the impacts of the other – remains largely underexplored. Above all, the link between these two stressors is missing where it matters most: in our policies which are designed largely in silos and are ungrounded in science. As a result of this, public health pays the price.

The State of Extreme Heat and Air Pollution in India – and Current Policies That Tackle Them

In 2024, 95% of the Earth’s surface temperature was significantly warmer than the 1951–1980 average, with nearly one-third of global land areas experiencing the hottest year on record, according to the Global Temperature Distribution 2024. In the same year, India ranked 5th globally for the worst annual average PM_2.5 levels, with 13 out of the world’s top 20 polluted cities located in the country. Cities with over a million residents in India are growing fast, and this urban explosion is one of the most visible and irreversible anthropogenic interventions, fundamentally driving socioeconomic changes, and reshaping our relationship with environmental stressors. According to long-term records of the Indian Meteorological Department (IMD), 2024 was the hottest year in India since 1901. Several studies have pointed towards India’s growing concrete jungles and chaotic urban planning as causative factors behind rising temperatures, contributing to around 60% of warming in Indian cities.

Temperatures above 40°C, the threshold for heat waves, are now routinely breached across major urban cities, and the frequency of these very hot days has been rising over the past decade. While 228 cities in India met the National Ambient Air Quality Standards (NAAQS) for daily PM₂.₅ concentrations (60 µg/m³) in 2024, only 33 met the World Health Organisation (WHO) daily safe guideline (15 µg/m³).

In response to deteriorating air quality, the Indian government launched the National Clean Air Programme (NCAP) in 2019, flagging 131 cities (non-attainment and Million Plus) with an initial target to reduce particulate matter concentrations by 20–30% by 2024. However, many of these cities have consistently recorded particulate matter levels beyond the annual average safe limits, and the reduction goal has since been revised to 30-40% by 2026, quietly extending the timeline of the target year.

Meanwhile, Heat Action Plans (HAPs) have been created in several cities to manage the fall-out from extreme heat events.

Both these policies represent important steps in tackling climate and environmental risks in our cities, yet they do not speak to each other or, for that matter, to India’s own vision for how it views the future of urbanisation. Air pollution control and heat adaptation receive passing mentions in flagship urban renewal and development policies such as the Smart Cities Mission and Atal Mission for Rejuvenation and Urban Transformation (AMRUT), leading to the creation of separate systems or programs for each, instead of a coordinated approach — even though these urban challenges are deeply linked.

The Science Behind How Heat and Air Pollution Interact

The interaction of heat and air pollution manifests most directly through warm nights during hot summers, when high night-time temperatures suppress atmospheric mixing and limit the dispersion of locally generated pollutants. With the increasing frequency and intensity of heatwaves, and a lower focus on managing air pollution during summers, it is critical to dive deeper into this relationship to understand how best to develop policies that address both. While the combined impacts of heatwaves and air pollution are beginning to be understood, the way they interact to amplify their individual impacts through atmospheric chemistry pathways is less studied. This largely happens in two interconnected ways:

– First, atmospheric conditions with low wind speeds, strong temperature inversions, high surface temperatures, and intense solar radiation worsen particulate matter (PM₂.₅ and PM₁₀) pollution by creating a dome effect that traps the pollutants closer to the surface and reduces vertical mixing of air that aids dispersion. This stagnation reinforces Urban Heat Island (UHI) effects where dense built-up areas and concrete structures absorb and retain heat, slowing night-time cooling.

– Second, high surface temperatures accelerate photochemical reactions involving ozone precursors such as nitrous oxide (NO_x) and volatile organic compounds (VOCs), forming ground-level ozone (O₃). This interaction adds to the respiratory burden while also intensifying heat stress.

Together, these processes amplify their individual impacts and intensify health risks (figure 1 illustrates this).

Figure 1: Interlinked Mechanism of Heat and Air Pollution

At the same time, the seasonal dynamics of heat-air pollution interactions are equally critical and vary across regions and meteorological conditions in India. In inland regions such as Delhi-NCR and the wider Indo-Gangetic Plain (IGP), winters bring anti-cyclonic conditions and a shrinking planetary boundary layer, with low wind speeds and frequent temperature inversions. This prevents upward dispersion, increasing the surface concentration of certain primary pollutants like PM₂.₅ and NO₂, partially independent of photochemistry.

By contrast, during summers, high heat and intense solar radiation accelerate photochemical reactions, driving ground level (tropospheric) O₃ formation. Coastal regions like Mumbai benefit from sea breezes that enhance dispersion of PM_2.5. However, strong sunlight sustains ground level O₃ in summer, often persisting longer into winter than in inland cities due to maritime influences. Although pollution loads are much higher in winters, the intensity of heat and solar radiation in summers acts as a catalyst, amplifying the effects of air pollution.

Dual Stresses on the Human Body

A study of 10 major Indian cities spanning different agro-climatological zones found that air pollution caused more deaths on hot days, with mortality rising by 0.8% on warm days and by 4.6% on extremely hot days for every 10 μg/m³ increase in PM₂.₅. A review of 40 epidemiological studies found that the combined effects from heat and either O₃ or PM can harm both respiratory and cardiovascular health. Heat strains our thermoregulatory system and air pollution inflames our cardio-pulmonary system. They act in tandem, creating a compounding health crisis. Human bodies are sensitive to pollution, and its impact increases when coupled with high temperatures, creating a ‘double stress’ that is extremely hazardous.

A construction worker standing atop a building. Credit: Shantum Singh, Pexels.

The synergistic impacts are far greater than their individual effects. It would be fair to hypothesise that there is still much to learn about the pathophysiology of heat and air pollution. However, evidence shows that co-exposure to heat and air pollution is linked to higher mortality rates. Together, they induce imbalance in physiological processes, especially amongst vulnerable population groups such as the elderly, those with co-morbidities, and young children. The intersectional nature of their synergistic impacts also becomes apparent when considering that persistent exposure to air pollution contributes to deficient lung function among children, women in low-income households are exposed to higher levels of indoor heat and air pollution, and informal workers, such as those in the construction industry or engaged in gig work, suffer the greatest exposure to extreme heat with limited social protection measures.

Synergistic Impacts, Coordinated Action: Short- and Long-Term Policy Priorities

Heatwaves are now recognised as climate extremes and air pollution as a persistent environmental challenge, but together, they no longer represent a distant risk. Untangling this dual threat requires deeper scientific inquiry into where pollution comes from and why it persists, alongside critical reflection on why policies have struggled to break this cycle.

In 2024, New Delhi crossed 40°C as early as April, with temperatures nearing 46°C in June. That same summer, the 20 hottest cities in India – as recorded by the IMD – were concentrated across Haryana, Uttar Pradesh, and Madhya Pradesh. Following IMD’s heatwave alerts, Delhi rolled out its Heat Action Plan (HAP), as did other cities in the region. Simultaneously, air quality in the region hovered around an index value of 225, falling into the ‘poor’ category and triggering the Graded Response Action Plan (GRAP) under the Commission for Air Quality Management (CAQM).

While both the GRAP and HAP were invoked simultaneously, their implementation occurred independently, reflecting the limited cross-sectoral engagement on these dual environmental stressors. This fragmented response also means that there is little scope to address the amplified risk posed by their co-occurrence. Addressing this policy blind spot is critical for a future that embodies convergent action.

From an air pollution perspective, that means year-round action that tackles year-round sources such as transport emissions, and not just seasonal sources such as crop residue burning. A recent national-scale study noted that vehicular transport accounts for a staggering 85% of the VOC emissions and 53% of NO_x emissions (O₃ precursors). The O₃ generated from this vehicular pollution is amplified by extreme heat, and contributes to significant health impacts.

On the heat front, previous studies have highlighted the policy gap with respect to long-term heat resilience in HAPs. Their almost exclusive focus on ameliorating the immediate impacts of heatwaves has meant little attention being paid to addressing the structural issues of crafting heat-resilient cities that reduce the impact of urban heat islands and overall heat exposures.

A long-term view of these issues requires addressing not just the immediate fall-out of high air pollution and extreme heat, but tackling the systemic, structural issues that drive their synergistic threat. The dual burden of heat and air pollution must be tackled in an integrated approach and not as siloed emergencies. Below, is outlined a series of short-, medium-, and long-term actions to guide this effort:

Short-term actions:

– Strengthen early warning systems: Use local data to map compounding risks. Cities should be able to utilise the high resolution spatiotemporal data from local urban sensors to map out the co-risk zones and power real-time dashboards for targeted measures to be deployed more efficiently.

– Enhance public awareness of co-exposure: Craft an awareness campaign that outlines the compounded risk of simultaneous heat and air pollution is imperative. This can be teamed with existing messaging that is put out by respective agencies for public awareness during periods of poor air quality and extreme heat.

Medium-term actions:

– Integration of GRAP and HAP protocols: There is an urgent need to align the GRAP and HAP within a common framework that addresses climate–health risks in a coordinated manner. This integration should be reinforced by linking related efforts such as the National Clean Air Programme and State Action Plans on Air Quality. At the city level, a unified task force could coordinate implementation across sectors, enabling regional impact assessment and enhancing adaptive capacity.

– Combined heat-air quality index: India should pilot a composite indicator that integrates temperature, humidity, and air quality metrics into a unified public health risk scale. Similar tools already exist such as the Monterrey Combined Air-Pollution and Heat Risk Index that combines indices featuring additive and multiplicative formulations to evaluate their combined relationship to mortality. Similarly, the Shandong Air-Health Index combines non-optimal temperatures and the effects of air pollution to assess district-level health risks. These models demonstrate the feasibility of developing similar indices for Indian cities. A combined Heat-Air Quality Index could inform early warning systems, trigger timely emergency health responses, and guide risk communication when thresholds are breached.

Long-term actions:

– Urban greening & cooling infrastructures: Expanding urban greenery can significantly reduce the intensity of urban heat island effects. Global case studies have shown that increasing tree canopy cover by 10% can lower surface temperatures by 0.5–1.5°C in urban areas. By moderating local temperatures, such interventions can also help in reducing peak O₃ formation and manage the experience of extreme heat.

– Thermal comfort through indoor cooling systems: Promoting well-ventilated and centralised indoor cooling systems, combined with energy-efficient technologies that have low global warming potential (GWP), could enhance thermal comfort while reducing greenhouse gas emissions (e.g., CO₂, HFCs) and air pollutants (e.g., NOₓ, SO₂, PM) from power generation.

– Focus on blue-green infrastructure that promotes thermal comfort: Land-use plans that integrate parks, urban forests and water bodies can help cool cities through shading and evapotranspiration, acting as heat sinks. A study in Ahmedabad found that a large park combined with reflective north–south roads reduced local temperatures by 0.17 – 0.33°C. Roads oriented along the north–south axis receive less cumulative solar exposure, absorbing and retaining less heat – a cost-effective strategy to mitigate the urban heat island effect. This, in turn, can indirectly curb ground-level O₃ formation and aid in the limited removal of air pollutants.

– Cross-cutting institutional readiness: Urban planning/city planning departments are a key nodule to systematic redesigning of urban zones. Coordinating with the departments of pollution, health, water, labour, and disaster management collaboratively would be more urban resilient. Training of local authorities and professionals involved in respective departments should be well-equipped with Standard Operating Procedures (SOPs) for timely response.

These recommendations, if implemented in an integrative and sustained manner, can build the momentum needed for collective action towards heat-air pollution challenges.

Hot Takes, Cold Action: How Heat is Misplaced Within India’s Bureaucracy

Extreme heat is no longer a distant threat. Over the past few years, it has claimed lives, destroyed crops, disrupted governance, and pushed India’s systems to the brink. In 2022, intense heatwaves devastated wheat crops, prompting an export ban. A year later, over 600 people suffered heatstroke at a state award ceremony in Khargar; 12 died. And in 2024, at least 33 people, including election officials, died from suspected heatstroke during the Lok Sabha elections.

This year is no exception. February 2025 was India’s hottest in 125 years, with many states breaching 40°C. Reports of heat-related deaths came in from Telangana, Gujarat, Punjab, and Odisha. Yet, despite these rising impacts, extreme heat continues to be treated by the bureaucracy as a seasonal, static, and short-term risk. In reality, heat is complex, pervasive, and deeply unequal in how it impacts different communities and sectors.

As part of our recent study on the implementation of heat resilience measures in nine Indian cities, we spoke to 88 officials across disaster management, health, urban planning, and labour departments. We found a fragmented and often inadequate understanding of heat as a policy issue which directly shaped actions and responses.

Map from SFC’s latest report showing some of the Indian cities that are likely to see the biggest rise in extreme heat index days in a 1.5°C world.

This blog draws on those conversations. It unpacks why heat remains overlooked by many parts of the Indian state, and what it will take to shift that mindset.

Bureaucracy misunderstands the threat of heat

The way bureaucracy responds to heat as a policy issue is fundamentally shaped by its understanding of the threat. This understanding – or often – misunderstanding, is influenced by two key phenomena: the rapidly changing nature of extreme heat, and the diverse, pervasive ways it impacts the population.

India has historically been a hot climatic zone, making heat a familiar presence. However, the extreme heat we face today is unprecedented, escalating at a much faster pace with threatening increases in heatwave days, humid heat days, and warm nights. This rapidly evolving nature of heat is a far more serious policy challenge than it is currently understood to be. Given the alarming rate of change, it becomes crucial for the bureaucracy to internalise this dynamic threat and adapt its response mechanisms accordingly.

Heat also impacts every sector and individual differently. Its impacts differ based on factors like the nature of work, built environment, and physiological conditions of an individual. Impacts spread from the workplace, affecting productivity and wage loss, to homes and public spaces, often hitting vulnerable, invisible groups the hardest. Many of these second and third-order effects are difficult to see and often go overlooked.

This inadequate understanding of heat’s complex, pervasive, and evolving nature shapes how the Indian bureaucracy currently responds to it: as a static, seasonal, and contained risk. As a result, heat actions are skewed towards short term reactionary measures, rather than long-term solutions.

During our fieldwork, we observed this misperception in three significant ways: first, in how heat is contained within bureaucratic memory; second, in how heat actions are currently implemented at local levels; and third, in how the state understands and records the health impacts of heat.

1. Bureaucratic memory around heat is seasonal

Heatwaves are still not fully understood by our systems, both in form and intensity, rendering them largely invisible. Heat seasons are often seen to last specifically from April to July, without much room for recognising their severity and preparing for the threat beyond these months. One official summed up this approach by remarking, “Now heat is past and we need to move on,” explaining how heat was no longer seen as a threat, with their focus shifting to the next seasonal issue – the monsoons.

This seasonal outlook towards extreme heat also means that even the most severe episodes of heat get treated as isolated events, not as signals of a growing, structural threat. This is partially due to a lack of technical capacity to understand the changing nature of the threat, coupled with shortage of staff. For an already overburdened local bureaucrat, a sentiment echoed by one who said, “There is so much work in the existing things which we have to do, let alone doing anything separately on our own,” there’s almost no institutional room for heat to be addressed. The result is a governance cycle defined by reaction rather than preparedness, falling short of being able to build any form of long-term adaptive capacity.

2. Heat actions lack local ownership and heavily depend on top down guidelines.

Effective heat actions must be locally driven, given their hyperlocal impact. However, current heat governance is heavily influenced by rapid response guidelines from state and central departments. We found this in response to questions on agenda-setting, as one official remarked, “We are waiting for guidelines from above.”

This strong dependence on national or state directives, from ‘dos and don’ts’ and awareness materials to specific funding, severely limits local ownership in solving for heat. As another official expressed, “It’s simply not on the agenda. If the central government issues directives or even encourages public awareness, then something will happen.“

These rapid response guidelines, while immediate, are filling a gap for a quick fix and a short time. They tend to be issued annually, acting as a temporary measure rather than fostering long-term, integrated solutions. However, their short term nature and a one-size fits all approach makes them an ineffective measure to build long-term adaptive capacity for heat, failing to protect the most vulnerable groups and address specific, evolving needs on the ground.

3. Invisibility of heat death reporting

The true human cost of heatwaves in India often remains obscured, primarily due to significant underreporting of heat-related deaths. While heatwaves are the deadliest natural hazard in Indian cities, official figures paint an incomplete picture. For instance, in 2024, India experienced a staggering 536 heatwave days (the cumulative total of heatwave days across all regions of India), the highest in 14 years, according to the India Meteorological Department. The official data reported only 41,789 suspected heatstroke cases and 143 heat-related deaths, a figure expected to be severely underreported.

This is partly due to the very nature of heat and how it presents during medical evaluations, from routine check-ups to emergency situations. Heat usually rides on – or hides behind – other medical conditions such as heart failure, respiratory distress, kidney dysfunction, or exacerbated pre-existing illnesses. This invisibility of heat as a ‘trigger’ often gets masked by the more immediate, observable physiological failures. It is, therefore, very hard to accurately attribute a death solely to heat, making it challenging for medical professionals to list it as the primary cause of death on certificates.

Despite the challenges in accurately attributing deaths, past experiences with high-mortality heatwave events have, paradoxically, played a crucial role in shaping future actions on the ground. As one official revealed, “Deaths this year have helped provide the services. This has helped create pressure. First time I have heard hospitals created heat wards.”

With low estimates of deaths in the official records, media coverage of heatwave deaths also often serves as a catalyst for bureaucratic action. Furthermore, an official highlighted the role of the media, explaining, “If anyone suffers from the heat, the media covers it extensively. Bureaucrats are keen to avoid negative publicity, so even if some of the actions seem superficial, they do get implemented effectively.” This underscores how the visibility of public health impacts, whether through media or, ideally, accurate official data, can push government bodies to address the issue.

How we see heat matters

The prevailing view of heat as a slow, silent threat has led to deep bureaucratic underestimation of its urgency. In our study, we found that heat actions in India are currently driven by short-term measures directly linked with how bureaucracy perceives heat, often missing out on major long term measures that could help build community resilience and enhance adaptive capacity. In cases where we found long-term actions being implemented, they were poorly targeted.

While national guidelines and central mandates have helped make heat visible as a public health issue within the bureaucracy, a comprehensive approach requires a fundamental shift in perception. This starts with building capacity both within institutions and the bureaucracy to assess, track, and respond to this evolving threat. It also means looking beyond traditional disaster management and integrating sectors such as labour and urban planning into heat discussions. Solutions must account for the ripple effects of heat: school closures, reduced work hours, infrastructure stress, agricultural losses, and more.

Finally, effective heat action needs to stem from the ground, locally owned by those directly affected by it. This necessitates targeted vulnerability mapping and active community involvement, as heat will impact those most who are already at the brink of survival. Dedicated funding channels, coupled with active community engagement and the involvement of stakeholders most impacted by heat in their daily lives, are crucial. This approach ensures that interventions go beyond temporary relief, tackling the fundamental sources of vulnerability, such as dangerous employment or living conditions, for lasting resilience. Only then can heat resilience become an embedded, continuous part of planning, policy, and decision-making.

Tamanna Dalal and Aditya Valiathan Pillai contributed to this article.