Heatwaves make daily life uncomfortable, but also pose a serious threat to human health and the environment. Here is our guide to getting through one.
The oppressive temperatures of a heatwave can have far-reaching impacts, from risks to human health to destroying crops and increasing the risk of wildfires. In 2019, extreme heat is estimated to have caused the deaths of 356,000 people worldwide, according to one set of estimates, making it one of the most dangerous yet overlooked natural hazards. While there is still a great deal of uncertainty about toll that heatwaves take (the World Health Organization estimates 166,000 people died between 1998 and 2017, by comparison), there is little doubt that the number of people exposed to heatwaves around the world is increasing.
And climate change is only likely to make heatwaves more frequent and intense in the future. Over the years, BBC Future has covered many different aspects of living with and enduring extreme hot weather. Here we round up some of what we have learned.
How do you stay cool in a heatwave?
It’s crucial to stay cool in hot weather as it can have serious effects on your health (see further down this page). Fortunately, there are some simple steps you can take to find relief when the temperatures climb to uncomfortable levels.
Keeping out of the sun between 11am to 3pm – usually the hottest parts of the day – either by staying indoors or in a shaded area, is an obvious step. It is also important to drink plenty of liquid, including hot and cold drinks (unless it is very humid, in which case hot drinks aren’t the best idea). But it’s best to avoid drinking lots of alcohol, although a beer or two may still help to hydrate you.
Eating foods with high water content such as strawberries, cucumber, lettuce and watermelon can also help you to stay hydrated. Spicy and hot foods have also been shown to help us stay cool by making us sweat more.
While the evidence on the colour of clothing is mixed – there appears to be little difference between wearing light or dark clothing as a study of Bedouin tribes in the 1980s revealed – wearing loose-fitting clothes can help by allowing air to circulate next to your skin.
You should also think twice before you open all the windows of your house to keep cool – if the temperature if higher outside than inside, you might lose a possible cool haven. Close the curtains in rooms where they face the sun instead.
One of the easiest ways to stay cool can be to take advantage of the temperature change in the air when water evaporates. Taking a cold shower or a swim can help you cool down quickly. Ancient societies placed earthenware jars of water or wet sheets in front of a window or a draughty spot, helping to cool the air as it passes over it. This can also work if you are using a fan by blowing the air over a bowl of ice or cool wet sheet.
However, the evidence on the effectiveness of fans is quite mixed, largely due to a lack of good quality randomised trials. Generally, fans are thought to help in temperatures up to 35C (95F), but above that blowing hot air across the body could make the situation worse and even increase dehydration. It’s also worth remembering that fans use motors to work, and so generate some heat of their own while running, so it is a good idea to keep a window ajar to improve the flow of air.
In the longer term there are a huge variety of ways we could adapt our houses and buildings to stay cooler in high temperatures, from wind catchers – towers which create cross ventilation in buildings and have been used by societies for millennia, to green roofs and corridors. Trees are an amazing way to keep cities cool – and even a single tree in a street or a garden can provide measurable cooling benefits. Meanwhile, cities such as Tokyo have experimented with new ways to keep a wider city cool, from solar-blocking paint to new types of low-energy air conditioning.
Sleeping in a heatwave
Temperature plays an important role in the human sleep cycle (and that of all mammals). As our bedtime draws near, our core body temperature typically falls along with our heart rate, and is thought to increase the familiar sensation of sleepiness. The veins in our hands and feet also open up to allow more blood through them, increasing the temperature of our skin and increasing heat loss.
But on hot, sticky nights, it becomes harder for our bodies to lose heat, meaning our ability to drift off to sleep is also affected. Hot night-time temperatures can also lead to more disrupted sleep, leaving people feeling more tired the following day.
Bed-sheets, duvets and night-time clothing such as pyjamas help to create a microclimate around our skin that maintains this optimal temperature
The ideal room temperature for sleep is reported to be between 19-21C, although some research suggests we require our skin to be at a temperature of between 31-35C. Bed-sheets, duvets and night-time clothing such as pyjamas help to create a microclimate around our skin that maintains this optimal temperature.
And when temperatures begin to rise, our first instinct might be to throw off the bed sheets to expose more of our skin to the air to help us cool down. Unfortunately some research suggests this isn’t as helpful as you might think because it disrupts the body’s ability to control the temperature next to our skin through the night. So a thin sheet – rather than something thicker that might provide too much insulation – can help to ensure a better night’s sleep.
A better option might be to use a fan to increase the amount of air flowing over your body at night. Researchers have found that overhead or ceiling fans in particular help to distribute a gentle flow of air over the body, reducing the number of times people wake during the night.
Opening windows can also help if there is a gentle breeze, but in cities the noise from outside could only make matters worse. Keeping your curtains shut during the day, especially when the Sun is on the windows, can help to prevent your bedroom from heating up too much.