United Nations Office for Disaster Risk Reduction's Report On Heatwaves

Rising heat and its impacts on climate, ecosystems and urban livelihood have gathered enough attention during the last few decades, so much that institutions started long term planning, analysis and policy making. But, this phenomenon of extreme heat situations and their consequences are new and poorly understood, and worse, they have been growing in intensity and frequency for over the last few decades.


IPCC scientists predicted that if we fail to stop global warming at 1.5°C and the world goes for a 2°C rise in temperatures instead, it will increase the number of people  affected by heat waves by  420 million. Data from EMDAT shows that heat waves have increased 240% between 1980-1999 and 2000-2020. The asian region is diverse, both geographically and in terms of economic status, as a result heatwaves have a more severe adverse impact here.

Defining and Measuring Heatwaves

Large scale heat waves are a new phenomenon and therefore are poorly defined, also different regions have different thresholds of tolerance, depending on geography, local weather patterns and  economic well being of that population. Institutions have adopted various ways of defining extreme heat situations– EM-DAT defines a heat wave broadly in order to cover global reports: “a period of abnormally hot and/or unusually humid weather.”;  IPCC defines a heat wave as, “a period of abnormally hot weather” ; The Red Cross as “a prolonged period of excessive heat, often combined with excessive humidity.” 

Scientists believe it is more important to mitigate the effects of heat waves than to look for a precise definition. Heat waves forecasting has moved from just the maximum temperature of a place to the heat index which gives a better insight into how a human being is affected by the temperature. Also, extreme heat means different things for different groups and classes of people, like pregnant women and old people at risk  may perceive it differently, people who have to work outside in the open sun have different measures of ‘extreme’ and people with air conditioning have different. 

Challenges and Impacts

The prime challenge of estimating the number of deaths due to extreme heat situations is that it is pretty much impossible to establish any relationship between just another death and death by heat exposure. Deaths from many causes, including but not limited to cerebrovascular, cardiovascular, and respiratory diseases, and certain infectious diseases are major contributory factors for deaths due to heat waves but do not get captured during hot weather as they do for other disasters such as storms or floods.Developing and low income nations that don’t have robust systems in place to document heat related deaths report less casualties than actual and therefore present a weak case for policy change in their region.  As an example, Europe reported the most extreme heat related deaths in last decade despite the fact that asian countries have suffered more severe cases of extreme heat events because they use the method of ‘excess death estimation’. This method is used to estimate how many individuals may have died due to a particular event or process (in this case heat waves) compared to how many would have died without it. This method is effective and is  becoming increasingly popular in public health and epidemiology. 

Extreme heat situations result in various directly noticeable factors and less noticeable indirect impacts. More direct effects are things like  heat strokes, dehydration, more deaths from cardiovascular and respiratory diseases and a spike in the rate of hospitalizations; indirect impacts include increased accidents on road and work related, spreading of food and water borne diseases and disruption of power resources due to increased consumption.  In India, which has been under the spell of extreme heat waves for many consecutive years, the trend of increasing temperature is strongly correlated with the increase in diabetes and hypertension in urban population. Although weather conditions in a region are same for everyone, the effects that extreme heat has on people from different economic backgrounds are drastically asymmetrical, low income families and individuals don’t have access to air conditioning and cool water to drink or bathe in. These things along with access to health and emergency services are important for survival in extreme heat situations.

The most vulnerable groups of individuals are elderly people and pregnant or lactating women. Elderly people are vulnerable especially because they are more likely to be suffering with a disease or disability, further the signs of dehydration and heat stroke become harder and harder to assess with age, the body also loses ability to adapt to sudden temperature changes. Heat-related deaths in elderly have increased by 53% during the last decade. Many European and Asian countries are inching towards an aging demographic profile. The problem will only become more severe if not addressed soon. Same is the case of pregnant and lactating women, increase in heat and pollution in the atmosphere puts both the mother and the infant under stress. Moreover, dehydration due to heat exposure can have cascading adverse effects in pregnant and breastfeeding women, and their infants, including but not limited to still births, premature birth, low birthweight, and lactation suppression in mothers. Gender roles also play a role in exposing women to extreme heat as they are often responsible for cooking and cleaning in sometimes badly ventilated kitchens and fetching water from far away wells is also a phenomenon prevalent in many cultures. 

Possible Mitigations and Interventions

Building more sustainable cities should be first in the list for better adaptation to extreme heat, our cities are built primarily from two of the most heat absorbing materials– concrete and steel. Cities also have many vehicles and not enough trees. Urban poor are the worst affected bunch, they suffer bad living conditions in an expensive and ruthless environment of cities. A more targeted approach to alleviate their problems is needed on the local level, access to cool potable water and community cooling centers should be built. More sustainable building designs should be explored and adopted so the need for heat absorbing material and air conditioning can be reduced. Eco friendly transit systems and vehicles will help bring down the intensity of heat waves.

Special attention needs to be paid towards the effects extreme heat on women because they are more vulnerable to the negative effects of these situations, fetching water from far on sunny afternoons, handling pregnancy and childbirth without sufficient cooling systems, working pregnant women are also exposed to more direct heat while traveling to work or while working outside.

Governments– on large scale and small– should partner with NGOs and think tanks to collectively address the immediate needs of people regarding heat waves and move in the direction of positive policy change. New innovations in disaster risk mitigation and emergency health services should be encouraged and adopted  to tackle the threat of extreme heat events. 

Written By:

Vivek Anand

Vivek is a writer who writes to explore. His interests include philosopy, psychology, poetry, cinema, mythology and international relations. Above all he’s interested in making sense of complex systems-how they work and influence each other. An alumnus of Calcutta University, he has a bachelor's degree in Physics.

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