4 Things You Should Know About Heat Waves

They’re Caused by Trapped Air

Heat waves usually form when a strong high-pressure system settles over an area. In these systems, cool, dense air sinks toward Earth’s surface, compressing and warming as it descends. This creates a layer of hot air that acts like a lid over the atmosphere. 

The warm air trapped near Earth’s surface can suppress cloud formation and limit the movement of cooler air that would normally bring relief. As a result, heat builds day after day, and nights can stay warmer than usual too, giving the environment less time to cool down between peak temperatures than it normally would. 

A heat wave ends when the high-pressure system trapping the heat weakens or is pushed out by shifting weather patterns higher in the atmosphere. At that point, cooler air, stronger winds, clouds, or rainfall may move in and break up the prolonged heat.

Heat waves can occur almost anywhere, but they’re least common in polar regions and coastal areas where surrounding waters help prevent temperatures from staying extremely high for long. Recent events, however, have shown that coastal regions and both poles are now also experiencing more frequent and intense heat as the climate warms.

They Can Damage Infrastructure

Heat waves don’t just affect people; they also put infrastructure under immense pressure. Roads are often one of the first places the adverse effects show up. Asphalt can soften in extreme heat, and in some cases, roads can begin to buckle under the weight of traffic. Footage of unexpectant motorists going airborne over deformed roads vividly illustrates just how dangerous the conditions can be.

Rail systems, meanwhile, are vulnerable to sun kinks, the name given to tracks that bend and become misaligned in extreme heat. Not even aviation is immune: On extremely hot days, airports may delay or cancel flights because warm air is less dense, which reduces lift and can affect takeoff, especially for heavily loaded aircraft or on shorter runways.

The electrical grid we rely on is also increasingly burdened during heat waves, but for a different reason: demand. As temperatures climb, air conditioning usage spikes, and the surge can strain local grids. In severe heat waves, outages become especially dangerous because they disable cooling precisely when it’s needed most.

Nighttime Temperatures Stay High

A hot afternoon is uncomfortable during the summer, but at least there is usually the  cooler evening air to look forward to. During extended heat waves though, nighttime temperatures may barely drop at all, especially in humid climates and big cities. 

This is largely due to something known as the urban heat island effect, wherein densely packed buildings as well as concrete and asphalt absorb heat during the day and slowly release it after sunset, resulting in minimal change on the thermometer. 

That means the body doesn’t get the much-needed chance to recover from daytime heat stress. When nighttime temperatures fail to fall below about 68 degrees Fahrenheit, meteorologists refer to the phenomenon as a tropical night — even in regions that would never otherwise be considered tropical. 

They Can Be More Dangerous Than You Realize

When you think of dangerous weather, you may picture tornadoes, hurricanes, thunderstorms, or floods — but according to the EPA, extreme heat is the leading weather-related cause of death in the U.S. The true toll may not even be known, as heat-related injuries are often underreported or attributed to other causes.

Extreme heat puts a lot of strain on the body. As core temperatures rise, blood vessels expand and the heart works harder to circulate blood. At the same time, sweating causes water and sodium loss, the latter of which is essential for helping maintain blood pressure, nerve function, and muscle control. High humidity also makes your sweat evaporate less effectively, making it harder to cool down.

The tricky thing about heat waves is that there’s no visibly destructive force like there is with other weather events — just steadily rising temperatures that can sneak up and overwhelm the body before you may realize. It’s important to avoid the high heat of the day when possible and to stay hydrated by drinking plenty of water and eating salty snacks to help replenish the salt your body loses when it sweats.