What is a heat wave?

July 7, 2020 | Environment
Heat waves: a period of two or more consecutive days with apparent temperatures exceeding 105°F to 110°F | Photo: Creative Commons

A heat wave, or heatwave, is a period of two or more consecutive days with apparent temperatures exceeding 105°F to 110°F (40°C to 43°C) on National Weather Service's Heat Index.

The temperature standards may vary significantly for different cities, states, nations, and regions.

What causes heat waves? A heat wave forms when high-pressure systems force air downward, preventing the air near the ground from rising.

The sinking air traps the warm air which prevents evaporative cooling, causing the trapped air to get hotter.

Heat waves can be particularly dangerous - 175 to 200 Americans die from heat in an average summer.

Air pollution plays a significant role in the deadly nature of heatwaves.

Scientists concluded that more than 40,000 people died due to a heat wave that hit Europe during the summer of 2003.

In 2010, the record-breaking heat that struck Moscow killed more than 10,000 citizens.

Heatwaves unfold over days and weeks.

As a result, death tolls are calculated by taking the total number of fatalities observed and adjusting that total based on the number of deaths that would typically have been expected.

Air pollution: one of the main causes of heat waves | Photo: Creative Commons

Air Pollution

High temperatures and air pollution often go hand in hand.

They appear at the same time and place, so it can be difficult to tell whether they acted individually or collectively.

The stationary domes of upper-level high-pressure that can lead to heat waves also tend to produce multiple days of sunshine and stagnant air, conditions ideal for the formation of ground-level ozone, and the accumulation of small particulates in the atmosphere.

Researchers are not yet sure of the extent to which heat and pollution have a synergistic effect, as opposed to acting independently.

However, data collected and analyzed from the National Morbidity, Mortality, and Air Pollution Study (NMMAPS) concluded that ozone did tend to boost the link between hot weather and deaths related to heart disease.

Researchers found out that an increase in temperature produced about one percent more cardiovascular deaths when ozone concentrations were at their lowest.

On the other hand, the increase was about 8 percent when ozone levels were highest.

The truth is climate change simulations indicate that heat waves may increase in number, duration, and strength across many parts of the world.

At the same time, an ever-greater proportion of the world's population is clustering in urban areas.

In the absence of stringent air pollution control, this trend could increase the amount of air pollution in a given area and the number of people vulnerable to its health effects.

Disasters such as hurricanes, tornadoes, wildfires, and floods often have people wondering whether climate change might boost such extremes.

No single weather event is caused by a changing climate, but research shows that human-produced greenhouse gases make some types of extreme weather more likely.

Therefore, heat waves are expected to become more frequent and intense in the coming decades.

As temperatures increase, more frequent and intense heatwaves could cause heat-related deaths to soar.

Forests and farmland could be swallowed up by expanding deserts, reducing crop output, and causing an even higher temperature spike.

The loss of plant life would reduce the Earth's ability to remove carbon dioxide from the air, amplifying the greenhouse effect.

And with vegetation drying up in the hotter regions, wildfires can spread uncontrolled across the globe.

The Heat Index

The Heat Index (HI) is a measurement that combines air temperature and relative humidity in a shaded area to produce a human-perceived equivalent temperature.

The "felt air temperature" or "apparent temperature" is the temperature an average person feels in the shade at a given moment.

For example, if the official weather stations indicate 32°C (90°F) and 70 percent relative humidity, the Heat Index is 41°C (106°F).

People feel it's hotter when the air is more humid because the human body cools itself by sweating.

When they evaporate, beads of perspiration help cool our skin.

But when the air is too humid, our built-in, natural cooling system no longer works so well.

Take a look a the Heat Index chart adopted by the National Oceanic and Atmospheric Administration (NOAA).

The Heat Index: a measurement that combines air temperature and relative humidity in a shaded area to produce a human-perceived equivalent temperature

The Worst Heat Waves of All Time

Prolonged episodes of heat triggered some of the worst weather events of the 20th and 21st centuries.

The cumulative impact of high temperatures can be especially deadly to those in poor health with little or no way to cool down.

On September 1, 1894, a heatwave in the Midwest led to a forest fire near Hinkley, Minnesota, where 400 people lost their lives.

On October 8, 1871, the Peshtigo fire killed 1,800 people in Michigan and Wisconsin.

Between 1936 and 1975, as many as 15,000 Americans died from problems related to heat.

During the record heat wave of 1936, the air temperature reached 121.8°F near Alton, Kansas.

On June 15, 1960, it was reported that a heat burst in Waco, Texas, caused the temperature to soar to 140°F (60°C) for a brief period, accompanied by winds of about 80 miles per hour (129 kilometers per hour).

In 1980, 1,250 people died during a brutal heatwave in the Midwest.

On January 12, 1980, Chinook winds carried warm air into Great Falls, Montana. In just seven minutes, the temperature rose from -32°F (-35.5°C) to 15°F (-9.4°C).

In 1983, North Carolina's thermometers hit 110.8°F.

In 1986, over 500,000 chickens died in Georgia during a two-day summer heatwave.

In July 1995, more than 700 people died in Chicago from high temperatures coupled with high humidity.

On one particular day, the afternoon air temperature reached 106.8°F at Midway Airport, followed by overnight low temperature of 84.8°F.

In May of 1996, temperatures rose from about 88°F (31°C) to 101°F (39°C) in the towns of Chickasha and Ninnekah in about 30 to 40 minutes.

On August 3, 2008, Sioux Falls, South Dakota, saw the temperature shoot up from about 72°F (22°C) to 101°F (39°C) during gusting winds of 50 to 60 miles (80 to 100 kilometers) per hour.

In the summer of 2003, tens of thousands died across Europe, including 14,000 in France alone.

During the winter of 2005-2006, hundreds of thousands of acres in drought-stricken Oklahoma and northern Texas were ravaged by wildfire.

In July 2006, air temperatures climbed to over 46.8°C (115.8°F) and killed more than 100 Californians during a two-week period.

On January 29, 2009, at 3 am, a heat burst maxed out thermometers at 107°F (41.7°C) in Australia.

In 2010, a record-breaking heatwave in Russia killed nearly 11,000 people in Moscow.

At the same, in Pakistan, devastating flooding inundated almost a third of the country.

Heat waves tend to occur over a relatively short period of time.

But they cause abrupt temperature changes with tragic consequences in people's health.

A single heatwave can kill hundreds and even thousands of people.

Severe drought also has an impact on water reserves, often forcing communities to ration water and restrict its use.

During periods of extended drought, vegetation often becomes extremely dry and, if sparked by lightning or a careless human, a dried-up zone can quickly become a raging inferno.

Wildfires: a consequence of heat waves and severe drought | Photo: Creative Commons

Heat Exhaustion and Heat Strokes

High temperatures and dehydration are a deadly combination.

Heat exhaustion occurs when people spend too much time under the sun, exert themselves too much, and don't drink enough fluids.

Symptoms include weakness, cold and clammy skin, paleness, fainting, irregular heartbeat, and vomiting.

In extreme cases, heat exhaustion may lead to death.

People exercising at sports or conducting drills in the military have already collapsed and died during heatwaves.

A heat stroke, also known as sunstroke, is a condition caused by the human body's overheating.

Hundreds of people die every year in the United States because of heat strokes.

Experiments show that the human body can withstand a temperature of about 250°F (121°C) for up to 15 minutes.

It has also been proven that a healthy person could withstand 364°F (184°C) for one minute and survive in a more extreme situation.

Cooking an Egg During Heat Waves

Meteorologists always refer to air temperature when noting down records and all-time highs.

Nevertheless, the surface of the Earth can get much hotter.

The highest soil temperature ever recorded was 200 °F (93.3 °C) at Furnace Creek, Death Valley, California, on July 15, 1972.

So, can you boil an egg on the ground? Yes. On a scorching day, you could cook an egg in California's Death Valley.

You will need a ground surface temperature of around 158°F (70°C) to cook an egg.

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