El Niño Returns: Escalating Heat and Haze Endanger Health Across Southeast Asia

The re-emergence of El Niño is amplifying climate stresses across Southeast Asia – driving hotter weather, prolonging dry seasons and increasing the risk of transboundary haze. A recent analysis from the S. Rajaratnam School of International Studies (RSIS), “CO26194 | El Niño, Heat and Haze: Health Implications for Southeast Asia,” warns that this cyclical climate phenomenon is worsening long-standing vulnerabilities and calls for co‑ordinated mitigation to protect millions of people. For complementary pleas to integrate climate and health action, see the WHO appeal at COP29.

Why El Niño Raises Heat and Worsens Air Quality

El Niño shifts atmospheric circulation patterns so that many parts of the region receive less rain and experience higher-than-normal temperatures. Those conditions foster more frequent and intense peat and biomass fires and cause prolonged periods of stagnant air. Stagnant layers trap fine particulate matter (PM2.5) and smoke at breathing level while elevated daytime heat and reduced overnight cooling reduce the body’s ability to recover from thermal stress. The net effect is a potentiation of both heat-related illness and pollution-related respiratory and cardiovascular disease.

Global monitoring agencies, including NOAA and the WMO, confirmed El Niño conditions in late 2023 with many climate models projecting impacts into 2024 – a pattern that already coincided with record warm spells in parts of the region. Meanwhile, the World Health Organization’s 2021 air-quality guideline lowered the recommended annual PM2.5 limit to 5 µg/m³, underscoring how frequently urban and haze-affected areas exceed safe thresholds during smoke episodes.

How Heat and Haze Combine to Harm Health

• High daytime temperatures increase dehydration, heat cramps, heat exhaustion and the risk of heat stroke.
• Elevated night-time temperatures compromise sleep and physiological recovery, accumulating heat strain over successive days.
• Smoke and soot from peat and forest fires generate fine particles that penetrate deeply into the lungs and enter the bloodstream, exacerbating asthma, bronchitis and heart disease.
• Concurrent exposure to extreme heat and heavy smoke multiplies risks – comparable to trying to recover from a fever while breathing through a clogged filter: the body cannot cool down properly and must also cope with reduced oxygen and inflammatory insults.

Lessons from Past El Niño Events

The 2015-2016 El Niño episode is a stark reference point: extensive peatland and forest burning in Indonesia produced thick haze that affected Indonesia, Malaysia, Singapore, southern Thailand and beyond for weeks. Haze episodes pushed air-quality indices into “hazardous” ranges, overwhelmed clinics with respiratory cases and caused widespread school closures and economic disruption. While precise tolls vary by study, such events have been associated with thousands of additional hospital visits, significant lost work days and multi‑million‑dollar economic losses across the region.

Populations at Greatest Risk

The health burden is uneven. Those most exposed and least able to adapt include outdoor workers in agriculture and construction, residents of dense low‑income neighbourhoods without access to reliable cooling or clean indoor air, people with chronic respiratory or cardiovascular conditions, young children and older adults. Migrant and informal-sector workers often face language, legal and accessibility barriers that limit their access to warnings, healthcare and workplace protections.

Typical Vulnerabilities and Immediate Household Responses

• Outdoor labourers: increased heat illness and smoke irritation; strategies include shifting work hours, taking extra breaks and improvising shade.
• Children and older adults: higher risk of severe respiratory and cardiac complications; households often keep them indoors and increase clinic visits.
• Low-income urban households: persistent indoor heat and haze infiltration; coping measures range from makeshift ventilation to buying masks or fans when funds permit.

Hidden Socioeconomic Costs

Hospital admissions and emergency visits are only part of the impact. Heat and haze impair everyday life: students miss school on poor-air days, wage earners lose income when outdoor labour is curtailed, and families spend more on medications, masks and temporary cooling. These indirect effects – lost productivity, interrupted schooling and increased caregiving obligations – amplify inequities and can convert temporary shocks into prolonged financial strain for vulnerable households.

Health systems experience less visible pressures too: routine services such as immunisation drives and maternal health outreach can be deferred, primary-care clinics may be redirected to manage acute respiratory caseloads, and workforce fatigue increases during prolonged events.

Policy Solutions: Regional Coordination and Local Preparedness

No single intervention will suffice. Effective responses require combining international cooperation on land management and emissions with targeted local measures that reduce exposure and strengthen health services. Priority actions include:

• Enforcing and strengthening no-burn regulations, increasing transparency of land concessions and holding actors accountable for illegal land-clearing that fuels peat and forest fires.
• Building integrated early-warning systems that combine weather forecasts, satellite fire detection and ground air-quality monitors to issue actionable alerts.
• Pre-positioning medical supplies, scaling up mobile clinics for remote farming communities, and coordinating cross-border contingency plans for mass sheltering when AQI reaches hazardous levels.
• Investing in community resilience measures: subsidised certified respirators (N95 or equivalent), affordable air purifiers or clean‑air rooms in neighbourhoods, and training community health volunteers to support outreach and risk communication.

Design Principles for Effective Early Warnings

Early-warning systems should produce composite risk indices that trigger specific, pre-agreed responses – for example, thresholds that prompt school suspension of outdoor activities, adjusted working hours for outdoor labour, mask distribution or activation of cooling and clean-air shelters. Alerts must be multilingual, accessible to migrants and informal workers, and delivered through diverse channels: SMS, local radio, public-address systems at transit hubs and community networks.

Urban Planning and Community Interventions

City and neighbourhood design can reduce exposure over the medium term. Increasing tree canopy, expanding shaded rest points along pedestrian routes, retrofitting community centres as designated clean-air and cooling shelters, and implementing urban water-retention features to lower fire risk all deliver multiple co-benefits. Public works programmes can combine short-term employment with long-term resilience projects such as large-scale tree planting, creation of micro-reservoirs and retrofitting schools and clinics with filtration and cooling equipment.

Priority Support for High-Risk Groups

• Low-income urban families: provide free or subsidised respirators, establish neighbourhood clean-air rooms and distribute fans or energy-efficient cooling devices.
• Rural farmers: enforce burn bans, create shaded rest stations in fields, supply heat-safety training and maintain rapid-response firefighting capacity.
• Migrant and informal workers: deliver multilingual warnings, mobile health services, and stronger workplace protections that permit paid breaks and modified schedules during high-risk days.

Rapid-Response Playbook: What Works During a Haze Spike

A prepared, practiced playbook reduces confusion and limits harm. Key elements are: predicted AQI thresholds linked to clear public advisories; employers shifting outdoor tasks to cooler, lower-pollution hours; schools cancelling outdoor sports and using indoor, ventilated spaces; municipal distribution of respirators to vulnerable households; and clinics standing ready with extended hours for respiratory triage. Pre-arranged logistics for respirator stockpiles, mobile clinic deployment and temporary sheltering save critical time when a spike occurs.

Case in Point: Coordinated Action Reduces Impact

During previous haze crises, districts that combined early warnings with community distribution of high-quality masks, temporary clean-air rooms and adapted work schedules saw fewer emergency admissions and reduced economic disruption than areas without such measures. These examples show that advance planning – not only emergency response – is the most cost-effective path to protect health.

Conclusion: A Narrow Window to Strengthen Defences

El Niño-driven heat and haze events will recur. The scientific links between these climate patterns and increased heat and particulate pollution are well-established; what remains is the political will and investment to translate evidence into action. Strengthening integrated early-warning systems, enforcing land-use regulations, equipping communities with protective resources and embedding health into climate planning are urgent priorities to prevent seasonal disturbances from escalating into recurrent public‑health crises across Southeast Asia.

The RSIS commentary “CO26194 | El Niño, Heat and Haze: Health Implications for Southeast Asia” offers a concise policy roadmap. Policymakers, regional organisations and civil society must act now to reduce vulnerability and safeguard health as El Niño returns.