Is it true that the "proportion of tropical nights" is increasing year by year? Verified with Osaka data from the past five years

Summer townscape with tropical nights

I feel like "sleepless nights" are increasing...

Even at night, the heat does not subside and it is difficult to fall asleep.
Do you have any idea of such a "sleepless night"?

Recently, I often hear the voice that "tropical nights are increasing".
In fact, this trend is clearly evident from the data of the Japan Meteorological Agency.

In this article, we will explain how the proportion of tropical nights has changed using Osaka as an example, while visualizing it.

What is a tropical night? Definition and Basic Knowledge

"Tropical night" is a night when the minimum temperature at night is 25°C or higher.
To be clear, if the minimum temperature from the evening of the previous day to the morning of the day is 25°C or higher, the day counts as a tropical night.

What you need to pay attention to is not only the "heat of the day", but also the "loss of coolness at night".

[Data Comparison] Tropical Night Trends in Osaka (2020-2024)

Here, we will compare the frequency of tropical nights in July over the past five years.

2020: 11th (about 35%)
2021: 13 days (about 42%)
2022: 15th (about 48%)
2023: 18th (about 58%)
2024: 21st (about 68%)

*July of each year is calculated as 31 days.

👉 With each passing year, the rate of tropical nights is steadily increasing. **

Why are tropical nights on the rise?

The increase in tropical nights can be attributed to the following factors:

Heat Island Phenomenon
→ Heat accumulated on asphalt and buildings is released at night, making it difficult for urban areas to cool down
Progress of Global Warming
→ Rising annual average temperatures are also affecting nighttime
Dense housing and poor ventilation
→ Natural heat dissipation and wind flow are obstructed, making it easy for heat to accumulate

Health Risks Posed by Tropical Nights

If your body temperature does not drop at night, the quality of your sleep will decrease.
Lack of sleep can lead to problems such as:

Poor judgment and lack of concentration
Increased risk of heat stroke (accumulation of fatigue)
Mental balance disturbance (irritability and depression)

"Tropical Night Countermeasures" that you can do today

✅ Fan and air conditioner combined (circulate the wind)
✅ Shower or foot bath before bed (lower your body temperature before going to the futon)
✅ Use of cooling bedding and ice nonn
✅ Open the windows slightly to create a path for the wind (be careful of crime prevention)

Conclusion |"Heat" creeps up even at night

We tend to focus only on the heat of the day.
However, it is during the "unprotected time" of sleep that the influence of temperature is greatly revealed.

The feeling that the night has become hot is not just the fault of the mind.
I hope it will be an opportunity to reconsider my life based on both experience and data.