Why Is Summer in Japan So Hot? A Foreigner's Guide to Japan's Humid Summers and Heatstroke Prevention

 Every summer, I find myself thinking the same thing:

"Was Japan always this hot?"

Many people around the world are feeling the effects of climate change, and average temperatures continue to rise year after year.

Japan is no exception.

In recent years, Japan has seen more extremely hot days, more tropical nights, and longer periods of intense summer weather.

Before moving to Japan, I had experienced hot summers in Korea as well.

But after living in Japan, I quickly realized that the biggest difference wasn't the temperature itself.

It was the humidity.

Even when the temperature is "only" 35°C (95°F), summer in Japan often feels much hotter and more exhausting than the number suggests.

After walking outside for just a few minutes, your clothes can be soaked with sweat, and even after sunset, the air often feels heavy and uncomfortable.

If you're planning to visit Japan in summer, or if you've recently moved here, understanding Japan's unique climate can make a big difference.

As a foreign resident living in Japan, I'd like to share what makes Japanese summers feel so intense and how locals deal with the heat.

The Real Reason Japanese Summers Feel So Hot: Heat and Humidity

The biggest characteristic of summer in Japan is not simply high temperatures.

It's the combination of heat and humidity.

There are many places in the world that are hotter than Japan.

Parts of the Middle East, Southeast Asia, and the southwestern United States regularly experience temperatures above 40°C (104°F).

However, Japan often feels more uncomfortable because of its humidity.

When humidity levels are high, sweat does not evaporate easily from our skin.

Normally, the evaporation of sweat helps cool our bodies.

But in humid conditions, that cooling system becomes much less effective.

As a result, body heat builds up more quickly, increasing the risk of heat exhaustion and heatstroke.

This is one reason why Japan sometimes issues heatstroke alerts even when temperatures are around 30°C (86°F).

Dry Heat and Humid Heat Feel Completely Different

Many foreigners are surprised by how difficult Japanese summers can be.

I've heard people from Europe, North America, and the Middle East say:

"I've experienced hotter temperatures before, but Japan somehow feels harder to handle."

The difference is humidity.

In dry climates, stepping into the shade often brings immediate relief.

In Japan, however, humidity levels of 70% to 80% are common during summer.

When temperatures reach 35°C with humidity above 80%, the heat index can feel closer to 40°C or even higher.

This heavy, sticky feeling is something many visitors don't expect before arriving in Japan.

Summer Feels Different Depending on Where You Live in Japan

Another interesting thing I've noticed after living in Japan is that summer doesn't feel exactly the same everywhere.

Different regions experience the heat differently.

I currently live in Narita City in Chiba Prefecture, near Tokyo.

The Kanto region, including Tokyo, Chiba, and Saitama, often feels extremely humid because of moist air coming from the Pacific Ocean.

Large cities also experience the heat island effect caused by asphalt roads and dense buildings that trap heat during the day.

As a result, temperatures often remain high even late at night.

Sleeping without air conditioning can be difficult during the hottest weeks of summer.

The Kansai region has its own type of summer heat.

Cities such as Kyoto and Osaka frequently experience very high daytime temperatures.

Kyoto in particular is famous for its basin geography, which traps heat and limits airflow.

It's not unusual for temperatures to exceed 38°C (100°F) during the peak of summer.

In my experience, Kanto summers often feel more humid, while Kansai summers can feel more intensely hot during the daytime.

Of course, weather changes from year to year, but many residents notice these regional differences.

Heatstroke Has Become a Serious Issue in Japan

Heatstroke is becoming a growing concern across Japan.

Every year, thousands of people are hospitalized due to heat-related illnesses.

Older adults and young children are considered especially vulnerable.

Many elderly people may not feel thirsty even when they are already becoming dehydrated.

Children, on the other hand, have less developed temperature regulation systems and can become overheated more quickly than adults.

Because of these risks, schools, local governments, and businesses have strengthened their heat safety measures in recent years.

Outdoor activities are sometimes canceled based on the WBGT index, which measures heat stress by considering temperature, humidity, sunlight, and wind conditions.

Sports clubs and school activities may also be suspended during extreme heat warnings.

Common Heatstroke Prevention Tips in Japan

If you're spending summer in Japan, you'll quickly notice that stores are filled with products designed to help people stay cool.

Some of the most common items include:

• Neck coolers
• Cooling towels
• Portable fans
• Salt tablets
• Sports drinks
• UV umbrellas and hats

However, the most important advice may be the simplest:

Don't push yourself too hard.

Many cases of heatstroke happen because people think:

"I'm probably fine."

Regular hydration, taking breaks, and avoiding unnecessary outdoor activities during the hottest hours of the day can make a huge difference.

Using air conditioning is also important.

Electricity prices have increased in recent years, but many people in Japan now see air conditioning as a necessity rather than a luxury during summer.

In my home, we live with three Bengal cats, so our air conditioner runs almost constantly during the hottest months.

The summer heat in Japan can be dangerous not only for people, but also for pets.

Learning to Live With Japanese Summers

Climate experts expect Japanese summers to continue becoming hotter in the future.

What was once considered a normal summer day can now become a health risk.

Because of that, I think it's important to change the way we think about summer.

Instead of trying to "endure" the heat, we need to learn how to live with it safely.

Use the air conditioner when necessary.

Drink water regularly.

Rest when your body tells you to slow down.

These may sound like simple things, but they are often the best protection against heatstroke.

As someone who has experienced summers in both Korea and Japan, if I had to describe Japanese summer in just one phrase, it wouldn't be:

"extremely hot."

It would be:

"a heavy kind of heat."

If you're visiting Japan or planning to move here, that may be one of the first things you'll notice too. 🌻