What is a heat dome? Mexico, Central America and US swelter in extreme temperatures

What is a heat dome? Mexico, Central America and US swelter in extreme temperatures

Millions of people across Mexico, Central America and parts of the US including Texas and Florida have been sweltering in extreme heat. Energy grids are strained as people try to keep cool and heatstroke has seen iconic Howler monkeys in Mexico dropping dead from the trees.

More than two dozen deaths have been attributed to the brutal heat in Mexico since March. Experts have warned that the worst may be yet to come. In Guatemala, heat and forest fires have led authorities to ban outdoor activities at school's in the country's capital city.

Meteorologists have attributed the extreme conditions to what is known as a heat dome. This weather phenomenon is trapping hot air over the region with temperatures surpassing 45C in some places.

What is a heat dome?

A heat dome is a weather phenomenon where a ridge of high pressure gets stuck in the atmosphere.

It traps hot ocean air like a lid or cap on a boiling pot. Hot air expands vertically into the atmosphere and high pressure pushes it toward the ground. It has nowhere to escape and compresses trapping even more heat underneath.

Winds are usually able to move high pressure around but with the dome stretching far into the atmosphere, these weather systems become almost stationary.

A heat dome can lead temperatures to soar well above what is normal.

On top of this, the ground begins to warm up, losing moisture and increasing the chance of wildfires. With low rainfall expected across many of the regions the heat dome is expected to cover, experts have warned of an increased risk of blazes breaking out.

A veterinarian feeds a young howler monkey rescued amid extremely high temperatures in Tecolutilla, Tabasco state, Mexico.
A veterinarian feeds a young howler monkey rescued amid extremely high temperatures in Tecolutilla, Tabasco state, Mexico. - AP Photo/Luis Sanchez, File

Are heatwaves becoming more common?

Since 1950 heatwaves have increased in length and frequency all over the world, as shown in a study published in 2020.

This research, carried out by scientists from UNSW Sydney and UNSW Canberra, found that the Mediterranean has experienced an increase of two and a half heatwave days per decade since 1950. The Amazon rainforest had an extra five and a half in the same period.

The worst increases globally have taken place since 1999.

Heatwaves increase the chance of prolonged droughts and the risk of wildfires. Southern Europe has already seen the impact of severe blazes and a lack of rainfall so far this summer.

There are health costs too. Last year's exceptionally hot and dry summer is estimated to have caused tens of thousands of heat-related deaths in Europe.

The consequences will be even more severe for cities, where the combination of buildings plus pavement plus concrete creates an ‘urban heat island’.

In Europe 75 per cent of the population lives in urban areas, making heatwave mitigation a pressing concern. Creative solutions can be found. - in Portland libraries are being used as cooling centres. But what are the best ways that cities can be heatproofed?

We’ve listed the top three strategies for reducing the effects of heatwaves and added three ways that you can handle the heat. Our personal methods all have an environmental focus.

What can your government do to help with the heat?

Tree planting

A study published in 2019 found that increasing tree cover in cities could dramatically lower temperatures. Whereas surfaces like roads absorb heat, trees cool their surroundings through transpiration: absorbing water through their roots and releasing it into the atmosphere. It was found that for the best effects canopy cover must be 40 per cent.

Barcelona - already famous for its tree cover at 25.2 per cent - has a 20-year master plan to grow that to 30 per cent by 2037. This a wise move as southern Europe is expected to suffer from increasing heatwaves as climate change increasingly takes hold.

Adding vegetation to buildings

Trees aren’t the only plant-based solution on the block with an increased focus on adding vegetation to buildings as a way of cooling them down. Like trees, plants reflect the sun’s rays - a benefit if they are placed over heat-absorbing concrete - and cool the atmosphere through transpiration.

Urban planting schemes are underway in Paris and designs have been pioneered in Italy by architect Stefano Boeri.

Water features

While fountains may seem like a luxury they can have amazing cooling effects in urban environments.

Water absorbs and can transport heat (making moving fountains better than stagnant ponds for reducing temperatures), provides drinking water for parched citizens and decreases air temperature through evaporation.

The City of London's adaptation plan includes building more fountains and in Thessaloniki, Greece, Chrimatistiriou Square has a bioclimatic design with water features to provide relief from the sweltering Mediterranean heat.

What can you do to keep cool during a heatwave?

Wear natural fibres

Clothes made from fabric containing microplastics release harmful chemicals into the ocean when washed and can harm marine life.

The good news is that breathable clothing made from natural fibres like cotton and linen can keep you cool and is better for the fish. While far from perfect in terms of production, natural fibres do biodegrade and their weaves absorb sweat and allow air circulation around the body, helping to keep you cool.

Cold peppermint tea

First things first - ditch the coconut water. While this may seem like a natural beverage containing many hydrating electrolytes, coconut farming is deeply damaging to tropical biodiversity.

Switch to the far more ethically farmed peppermint tea. Mint can be grown in many different climates and can even be sourced locally or grown in your back garden. A peppermint teabag in a glass of cold water will cool you down as the natural menthol will stimulate cold receptors in the body.

Create a cross breeze

A more environmentally friendly option than air conditioning is to create a cross breeze using a fan and an open window.

Position the fan across the room from the window and the cooling airflow created will make sure you get a good night's sleep. For really hot nights place a frozen water bottle in front of the fan, and then you can enjoy a cold bottle of water when you wake up in the morning.