Beautiful autumn leaves are almost finished!　What I found by researching the timing of “autumn leaves” in old diaries and poetry collections.

It was even “warmer” in the Muromachi period than now!

Autumn foliage has been delayed this year due to the extremely hot summer. In the Muromachi period (1333-1573), when was the best time to view the autumn leaves?

In the Muromachi period (1333-1573), the best time to view the autumn leaves in Kyoto was from late November to early December.

says Yasuyuki Aono, an associate professor at Osaka Public University. By examining old diaries and poetry collections written in the vicinity of Kyoto, such as “Kusane-shu” and “Jitsutaka-no-Koki,” it is possible to determine when Kyoto’s autumn foliage was at its peak, he says.

Cherry blossoms are said to bloom when the total average temperature from February 1 reaches 400 degrees Celsius. In the same way, according to Associate Professor Aono’s research, the best time to see the autumn foliage can be determined by calculating the total difference between the average temperature and 25.1°C on the days after September 30 when the average temperature is lower than 25.1°C to 546.6°C.

By calculating backward, the average temperature in October can be estimated from the “autumn foliage day,” the day when the leaves are at their peak. Then, the calculation is: “The first half of the 15th century was relatively warm,

“It is estimated that the first half of the 15th century was relatively warm.

This is why the autumn foliage was at the same time of the year as now.

In the latter half of the 15th century, however, the average temperature in October is estimated to be 14°C, as the autumn foliage day is often in mid-November. Incidentally, the average October temperature in Kyoto in ’22 was 18.1°C. It suddenly became colder.

In the 16th century, it was about 16°C. In the 17th century, we could not estimate it due to a lack of data, but it was about 16°C in the 18th century as well, and it dropped to about 14°C in the 1820s and 1830s. After that, the temperature has been rising steadily up to the present.”

The climate of the past is known on a half-yearly basis, based on grain yields and other data, but not on a monthly basis. Based on ancient records, Associate Professor Aono’s research aims to elucidate the temperature in the past on a monthly basis, such as the average temperature in March from the time of cherry blossom blooming, and the average temperature in October from the date of autumn leaves changing color.

In fact, the coldest period in 200 years was caused by solar activity!

During the period of the 1820s and 1830s, when temperatures dropped sharply, ancient records show that in many years, early November was a foliage day. It was during this period that the “Great Tempo Famine” occurred.

The 1820s and 1830s were cold, especially in Asia. The Asian region is easily affected by solar activity, and solar activity was inactive during this period. We believe this may be the reason for the lower temperatures.”

Aono’s research has revealed the extent to which temperatures drop during periods of solar inactivity.

The average temperature has risen more than 3 degrees Celsius in the last 200 years,

I attribute half of it to global warming, half to increased solar activity, and half to urban warming.”

For some reason, there are few references to autumn foliage in ancient records in the 17th century, and it is not known when the autumn foliage was in the 17th century, but Associate Professor Aono says that solar activity was inactive in the 1670s and 1680s. if there were cold periods in the 15th and 19th centuries, and even the 17th century, this would mean that a cold period has occurred every 200 years.

We are about to enter the 200th year. People are worried about disasters caused by global warming, but could it be that solar activity will become inactive and it will get colder?

Some researchers say so. But I don’t know what the future holds.”

If global warming continues… “Beautiful Autumn Leaves” will not be seen any more!

Tree leaves are exposed to sunlight and produce nutrients from their chloroplasts. This is called photosynthesis. Leaves originally contain green chlorophyll and carotenoids, natural pigments that support photosynthesis. When the weather turns cold and photosynthesis ceases, chlorophyll is broken down, the green pigment fades, and the yellow color of the carotenoids becomes prominent. This is why the leaves of ginkgo trees, for example, turn yellow. On the other hand, the reddish color is caused by an increase in anthocyanin, which has a red pigment.

When the temperature suddenly drops for two or three days in a row, trees turn red (yellow).

Associate Professor Aono says that Kyoto is famous for its autumn foliage because it is located in a basin, which cools down quickly.

What will happen if global warming continues?

The autumn foliage will be delayed,” he says. The leaves may not turn as beautifully as they would if the cold temperatures continue.

What about cherry blossoms?

Cherry blossoms will bloom earlier to a certain extent, but then they will slow down. Cherry buds go to sleep in winter and wake up when they are exposed to the winter cold. This is because it is difficult for them to wake up unless the temperature drops firmly in winter.

Will we see less beautiful autumn foliage due to global warming, or will we see a colder autumn? The best climate is one in which we can enjoy the changing scenery of the four seasons.

Yasuyuki Aono is an associate professor in the Eco-Meteorology Research Group at Osaka Public University. His research interests include the evaluation of the effects of climate change on plant growth, reconstruction of climatic conditions in the period before the start of modern meteorological observation, and research on the mechanisms of climate change, thermal environment in urban areas, and the effects of climate change on plant growth, using a combination of meteorological observations, climate data, plant growth data, artificial satellite data, and data from ancient records and documents. The thermal environment in urban areas and the thermal environment assessment of people living in urban areas are also being studied.