Heatwaves and extreme heat

A heatwave is a marked warming of the air, or the invasion of very warm air, over a large area; it usually lasts from a few days to a few weeks (WMO, 1992).

Heatwaves (sometimes referred to as extreme heat) vary according to the location of a particular region and the time of year and there is no universal way of defining or measuring heatwaves. Heatwaves can exacerbate urban air pollution which can affect the elderly, pregnant women and children. The heat stress burden is dependent on local climate and a humidifying effect can erase the cooling benefits that would come from trees and vegetation. Consequently, in humid climates humans can adapt to a lower temperature than previously thought.

The impacts of heatwaves can be very catastrophic as we saw in parts of South Asia and Europe from May to September 2022, where there were over 60,000  “excess deaths”; the number beyond what would have been expected under “normal” conditions based on historical data (Nature, 2023). Heat exposure- related loss in labour capacity resulted in average potential income losses equivalent to US$863 billion in 2022.

Europe was also badly affected by high and unusual temperatures in the summer of 2003 leading to health crises in several European countries and the occurrence of 70,000 “excess deaths” mostly seniors (Robine et al. 2008). Modelled estimates show that between 2000 and 2019, approximately 489,000 heat-related deaths occurred each year, with 45 per cent of these in Asia and 36 per cent in Europe.

One challenge with heatwaves is that we don’t know how much of the mortality data is due to heat. People might go to hospitals because of a work-related injury or a heart attack, but these will not count as heatwave incidents. It’s important to measure temperature-related deaths accurately and consistently

Globally 2.41 billion workers, or 70 percent of the working population are exposed to excessive heat. This results in 22.85 million non-fatal injuries and 18,970 deaths annually. Workers in Africa, the Arab states, and Asia and the Asia-Pacific are most exposed to excessive heat. In these regions, 93 per cent, 84 per cent, and 75 per cent of the workforce are affected, respectively. As daily temperatures rise above 34°C (93.2°F), labour productivity begins to drops by 50 per cent.

Heatwaves (sometimes referred to as extreme heat) interact with and amplify the impacts, magnitude, and severity of other hazards such as wildfire, drought, cyclones, urban heat islands, and hazardous air quality. A multi-hazard risk management approach is therefore recommended for heatwaves, including early warning systems and planning. In urban areas, consideration of night-time temperatures and urban heat island effects is important to determining appropriate thresholds for heatwave advisories. Sensible occupational safety and health measures could save US$361 billion a year, while the global scale-up of heat health-warning systems for 57 countries alone has the potential to save an estimated 98,314 lives per year.

Essential components of health impact-orientated warning systems and early action for heatwaves, include assessments of heatwaves and health impacts, definitions and methodologies, communication of warnings, intervention strategies, and longer-term planning perspectives for managing heatwave events (WMO and WHO, 2015). The United Nations Secretary-General's Call to Action on extreme heat, calls on countries and communities to:

  1. To protect the most vulnerable people from the impacts of extreme heat, reduce extreme heat risk and build their resilience.
  2. To protect all workers in all sectors through appropriate occupational safety and health measures based on a rights-based approach.
  3. To build sustainable multi-sectoral and multi-scalara partnerships that ensure development and implementation of comprehensive extreme heat action plans, strategies and solutions to build heat resilience.
  4. To accelerate the pace of the just transition away from fossil fuels and scale up investment in renewable energy.

Vulnerable areas

  • Regions that are more susceptible to heat waves: inland deserts, semi-deserts and Mediterranean-type climates.
  • Urban areas: higher temperatures during the summer due to buildings, roads, and other infrastructures absorbing solar energy.
  • Heat waves disproportionately impact the health of people who are elderly from those who are young.
  • Heat can also affect underprivileged social groups and poor people. For instance, people living in densely built, low-income neighbourhoods, with no open green spaces and lack of air conditioning.

Risk reduction measures

  • Early warning systems.
  • Establishing cooling centres.
  • Structural measures: air conditioning and cooling systems.
  • Heatwave risk assessment integrated into urban planning and health management policies.
  • Raise community awareness, build the the preparedness of the most vulnerable, and incorporate education on heatwaves wherever possible.
  • Protect animals.
  • Create green corridors.
  • Use reflective cool roofs and pavements.

Latest Heatwave additions in the Knowledge Base

Update
Human existence at 1.5°C of warming will be grim, but life at 3°C would be far more severe, especially in cities and low-income countries, warns the World Resources Institute (WRI) in a new report.
The Energy Mix
Rooftops under the sun in London.
Research briefs
This study found that widespread use of cool roofs in London during the 2018 heatwave could have saved 249 lives by reducing the city's temperature. Cool roofs and solar panels are effective at mitigating heat and saving energy.
University College London
A farmer takes a break in the midday heat
Update
An ageing global population is converging with record-shattering heat - driven by climate change. This article offers a look into scenarios where tragic outcomes could have been avoided with simple actions
Global Heat Health Information Network
A health worker checks the blood pressure of a patient at the mobile clinic in Ankatafana, Madagascar
Update
By 2050, older adults in Africa are projected to face significantly higher heat exposure due to rapid population growth and climate change, with an increase in extreme heat events. This will heighten health risks and put pressure on local services.
Conversation Media Group, the
Cover and source: Green Risk-Informed Resilient Development Corps
Documents and publications
This paper documents the outcomes of a year-long intervention designed to address climate challenges in Jodhpur, India utilising a mixed methods that featured the production of the documentary "Sanchay".
Street busy with people and traffic during the UK heatwave
Research briefs
A groundbreaking new study by a team of researchers from Arizona State University, University of Washington and the University of Texas at Austin reveals that extreme heat significantly alters how people go about their daily lives.
Arizona State University
Prison
Research briefs
MIT researchers found that overcrowding, poor staffing, and restricted movement worsen heat risks in U.S. prisons. Southwestern prisons face the highest heat, and climate change is worsening conditions, especially for non-white and Hispanic populations.
MIT News, Massachusetts Institute of Technology
Update
The city has 220 public schools, and thanks to the Trust for Public Land's (TPL's) Green Community Schoolyards programme, the asphalt playgrounds of these schools will be transformed into parks and green spaces, starting from one school to the next.
Climate Adaptation Platform
Uploaded on

Is this page useful?

Yes No
Report an issue on this page

Thank you. If you have 2 minutes, we would benefit from additional feedback (link opens in a new window).