Killer Heat Waves

With minimal fan-fair, the lurking dangers of spring heat waves has begun, yet few people to grasp and evaluate the real danger of their devastating effects. Recognizing those risks could be a matter of life or death.

After a brutal winter most of us are experiencing a respite from freezing temperatures and heavy precipitation.  Sudden spring heat waves do not provide man, beasts, or plants, time to gently adapt into summer warmth.  A clear increase in the number and duration of heat waves is being reported, increasing the risk to human health who are becoming more vulnerable Most areas can experience a 100 degree swing, going from -40 to 60 degrees Fahrenheit!  Why should this alarm you?

  • Heat waves are more dangerous than tornadoes
  • Heat waves kill more people than sharks.
  • Heat waves put more human lives at risk than blizzards, floods or lightning storms.
  • Eight of the ten major human loss of life events were connected to extreme climate with three are related to heat waves, a phenomenon that has historically received little attention.
  • A direct societal impact of heat is death. Tens of thousands of deaths have been reported.


As the UN puts if, "Assuming there is a pool of people at elevated risk of dying (“high-risk pool or vulnerable”) in a population at any given time, a hot episode increases the risk of dying for those individuals, decreasing the pool size, simply put heatwaves the perfect depopulation mechanism. Heat also potentially increases the recruitment of individuals into the high-risk pool from the general population.

Heatwaves also place an increased strain on infrastructure such as power, water and transport. Clothes and food retailing, tourism and ecosystem services can also be affected, such that there may be socioeconomic “winners and losers” from heatwave events. In some instances, heatwaves may even trigger social disturbances at a number of levels.

Heatwaves occurring early in the summer have been shown to be associated with greater impacts on death in the same population than later heatwaves of comparable or higher temperatures.

Heat Wave

Heatwaves are a pervasive natural hazard. Although there is no universally accepted definition, they are understood to be periods of unusually hot and dry or hot and humid weather over the duration of at least two–three days, usually with a discernible impact on human and natural systems. Natural systems are severely affected by the impacts sustained beyond the duration of a heatwave. Heat waves are coming early and are hotter as the years roll along. 

There are dry heatwaves and moist heatwaves.   

Dry heatwaves are often associated with stable periods of weather that bring clear skies and large inputs of solar radiation. Hot and dry conditions may also be accompanied by windy conditions, which can increase heat stress.

Moist heatwaves are characterized by very warm, oppressive, humid conditions throughout the day and night, often with nocturnal cloud cover, a feature that prevents loss of heat accumulated throughout the day and thus little night-time relief.

There are temperature thresholds that life can endure to survive-beyond that lies increased illness and death.  When considering heat waves you need to consider several things such as ambient temperature, thermal sensation, relative humidity, and your activities.

The gravest heatwave danger lies in areas with a highly variable summer climate or a clear hot season and, accordingly, may result from a range of large-scale meteorological situations and climate-related mechanistic processes.

Heat is usually a result of the synergistic effects of temperature and humidity, as direct exposure to radiation load does not usually occur in such sheltered environments.

Death Knell to Health

What can you expect for your health as the temperatures skyrocket?  The collapse of the ability of individual’s body to regulate its temperature through the blood stream or by sweating is one of the most commonly reported effects leading to death. The most vulnerable sectors of population to heat waves are elder and infants.

The problem with these large temperature variations with sudden onset is that your body does not have time to adapt or learn to deal with the heat. 

When excessive heat exposure overwhelms the body’s heat-dissipating mechanisms your core temperature rises. An increase of as little as one degree Celsius (1ºC) is detected by your thermo-receptors and that information is disseminated through your skin, deep tissue and organs. The thero-receptors convey the information to the hypothalamic thermo-regulatory center in your brain and vasodilatation (enlarging your blood vessels) by inhibiting the sympathetic center responsible for vasoconstriction, and the initiation of sweating through your cholinergic. Your skin (cutaneous) vasodilatation results in marked increases in blood flow to the skin and cardiac output at the expense of other major vascular beds -basically your other organs.  These cardiovascular adjustments to accelerate the transport of heat from the core to the periphery (arms and legs) for dissipation to the surroundings constitute a major stress on the cardiovascular system.  Now, imagine how complex it is with COVID causing blood clots or bleeding issues.

Initiation of sweating results in the production of up to two liters per hour of sweat, rich in sodium and potassium, depleting your electrolytes that keep your minerals balanced in your body. This poses additional stress on the cardiovascular system if the plasma volume is not properly restored – by intake of fluid, for example.

  • Heat stroke syndrome due to heat load and a rising body core temperature
  • Kidney disease
  • Lung disorders including aggravated asthma
  • Digestive disease
  • Diabetes fluctuations
  • Increases blood clotting
  • Cardiac problems
  • Poor therm-regulation or the inability to balance heat gains to, and heat losses from, the body.
  • Heat exhaustion,
  • Heat cramps,
  • Heat syncope,
  • Heat edema
  • Heat rush
  • Psychiatric illness

Indirect threats of heat waves include the flourishing of harmful algae capable of producing toxins in drinking water supply water bodies, increasing the risks of intoxication for the population.

Another indirect threat are the environmental and social resilience by reducing food and water supplies.

Synergistic effects of heat and poor air quality are likely to contribute to increased mortality and hospital admissions.

Burgeoning mega-cities, where the Uniform Heat Index effect is likely to result in added heat loads.

Some populations are more vulnerable and include age (being elderly or very young), having pre-existing disease, living alone, being socially isolated, homeless, not having access to heat– health information in a variety of forms, being immobile, suffering from mental illness, those working outdoors, or not being able to undertake self-care.


There are numerous examples where the population is not properly warned. Often, people are unaware even of the concept of heat waves and their effects on health. As a consequence, authorities’ warnings are limited to the minimum actions, such as hydration and, in some cases, recommendations on outdoor activities. Those warnings do not include details on specific health alerts. 

Implementation of early warning systems, improved communication, and  effective emergency measures during heat waves, including appropriate health services could somewhat mitigate the heat wave impact.


Feeling the heat: Recognizing the risks of extreme weather

Brief for GSDR – 2016 Update Heat Waves: A Growing Climate Change-related Risk
Polioptro Martinez1 and Erick R. Bandala *

1Universidad de las Americas Puebla, Mexico.

2 Division of Hydrologic Sciences. Desert Research Institute