Counting days: Formula for the best date of fall hiking in Kanto Region

We’re already nearing to the middle of October. But we can still spend our days with half sleeves in Yokohama. I personally think the weather now is that of September before, or immediately after the end of summer vacation when we were grade schoolers. Still, it’s something like compulsory to regard October as “middle autumn.” Travesty. We should accept the reality. And so, weather in October 2019 could be viewed as the end of summer! To prove the point, let me refer the temperature data for the last 30 years …

Though, persimmons are getting redder these days
 in an orchard of Niiharu 新治市民の森.

Er, well, this is the standard course of discussion when we talk about climate change, right? Recently, I’ve learned there is another curious way to look to the matter. In 2007, Japanese Meteorological Agency notified the public that they changed the way to calculate an expected date for the best autumn leaves in Kanto Region. Until then, they employed the data collected during the 1960s, and used this formula:

The expected days from October 1^st for autumn leaves to be the most beautiful in Kanto Region

= 3.99*(Average Temperature of the location during September of the year) – 43.61.

In 2007, using the data for 2002-2006, they changed the coefficients of this formula like

The expected days from October 1^st for autumn leaves to be the most beautiful in Kanto Region

= 4.62*(Average Temperature of the location during September of the year) – 47.69.

Inevitably, it’s much later for the best days of autumn hiking in forests of Metropolitan Tokyo area, compared with the days when the Beatles existed. Then, when should we plan to go out this fall?

When can we encounter this for 2019?

I’ve done a math. For Yokohama, we can take out the temperature data for September 2019 from here, and the average turned out to be about 26°C … No wonder we felt it was hot last month. Plugging in this number into the above formula, the expected days is approx. 72, i.e. 72^nd day from October 1^st. That is to say, we must wait till December 11^th to welcome the best forest scenery for autumn leaves … Hey, it’s almost Christmas, aka winter, isn’t it? Mmmmmmmmmmm …

I’ve just noticed it was like that 4 years ago.
 This is a photo I took in Segami Citizen Forest 瀬上市民の森
 in the middle of December 2015.
 More to Segami Forest next week!

Just being curious, I also counted the days for Doshi Village 道志村 whose average temperature in September 2019 was about 23°C which could be something Yokohama had 50 years ago in early fall. With this average figure, the days to be tallied becomes 60. i.e., In Doshi Village we could have the best colors for fall 2019 on 29^th of November. Well, it’s at least still in a month categorized as “autumn.” How about Yadoriki? I used the data for Minami-Ashigara City 南足柄市, a neighboring city for Matsuda Town 松田町 where Yadoriki Water Source Forest やどりき水源林 resides. The forecasted best day for autumn leaves will be on December 4^th. Please take your pick and mark the calendar for fall hiking with hot chocolate this year. It’s about two months from now … Long hot days ahead. *Sigh*

A Japanese zelkova (Zelkova serrata) has
 started to change the color of its leaves
 early this October in Doshi Village.

Yadoriki was like this last late November …

If you find an environmental issues in Kanagawa Prefecture, please make a contact with Kanagawa Natural Environment Conservation Center 神奈川県自然環境保全センター

657 Nanasawa, Atsugi City, 243-0121

〒243－0121　厚木市七沢657
Phone: 046-248-0323

You can send an enquiry to them by clicking the bottom line of their homepage at http://www.pref.kanagawa.jp/div/1644/