Isn't 2025 just about temperature? The true nature of "summer with too much humidity"
"Isn't it suffocating this summer?"
The temperature is of course high. But more than that, "I don't sweat", "It's not cool even if there is wind", "It's stuffy even at night"──
Many people may feel that way.
The cause is the "abnormally high humidity" in 2025.
In this article, we will explain in an easy-to-understand scientific way why the summer of 2025 may feel "more uncomfortable than the temperature".
The "experience" of hot and humid weather is not determined by temperature alone
The "heat" we feel is not determined by the temperature alone.
High humidity prevents sweat from evaporating and prevents body temperature from dropping.
This can have the following effects:
- The body does not get cold instead of the heat
- Sweating does not stop and dehydration is easy
- Risk of heat stroke surges
In other words, rather than "35°C and crisp heat",
"Humidity of 80% even at 31°C" is more burdensome for the body.
2025 is a double punch of "temperature + humidity"
This year's feature is that the temperature is high but the humidity is also high.
For example, looking back at the trends in Osaka in July 2025:
- Average temperature: 31.6°C (+1.3°C compared to last year)
- Average humidity: 80-85% for every day
- 70% of days have an discomfort index (DI) of 80 or higher
🔸 > If the discomfort index exceeds "80", it is a level that "most people feel uncomfortable".
What is the "Discomfort Index"? Rough explanation
Discomfort Index= An indicator of the perceived heat calculated from temperature and humidity
| Unhappiness Index | Sensory Guidelines |
|---|---|
| ～70 | Comfort |
| 71〜75 | Slightly hot |
| 76〜80 | Hot and sweaty |
| 81 or more | Very hot and uncomfortable |
In 2025, "DI81-84" is observed every day in many areas.
This is a level of difficulty in sleeping and living without air conditioning.
"3 Reasons" Why Humidity Doesn't Go Down
-
Rising Sea Surface Temperature
→ High sea temperatures around Japan, providing a lot of water vapor in the air -
Urban Heat Island Phenomenon
→ Concrete and asphalt store heat and are difficult to evaporate at night -
Changes in atmospheric pressure distribution (bias of the Pacific anticyclone)
→ More days when moist air stagnates and wind is difficult to pass through
Countermeasures: Focus on Humidity, Not Temperature
Information on heat stroke prevention is attracting attention.
🔷 > WBGT (Wet Bulb Black Bulb Temperature)
This is an index that represents "actual heat stress" including "temperature + humidity + solar radiation (radiant heat)".
- Less than 25: Caution
- 25-28: Vigilance
- 28-31: High alert
- 31 or higher: Dangerous (level of refraining from going out)
→ Even if the temperature is still a little over 30°C, it is dangerous if the WBGT exceeds 31.
Conclusion: The "Dangers of Summer" that Can't Be Measured by Numbers
Those who feel that "this summer is abnormal" are right.
There is a **humidity trap" that can be overlooked just by looking at the temperature.
💡 **Believe in your experience and get into the habit of checking the numbers. **
In the summer of 2025, when the risk of heat stroke increases,
Let's protect your body with a three-piece set of "temperature + humidity + sunlight".
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