1. Autumn Leaves Start at the Mountain Top and Move Down Toward the Foot
According to the official page for the Tateyama Kurobe Alpine Route, autumn leaves in this area begin around mid-September near the Murodo plateau, making it one of the earliest places in Japan, alongside Daisetsuzan in Hokkaido. The elevation difference from the summit to the foot is 1,975 m (about 1.2 miles), and visitors are guided to see the colors as they shift location [1]. This same movement appears in reports from mountain huts. A report from the huts in the Northern Alps (Ushiro-Tateyama area) updated on October 7, 2025, states that the "autumn leaf front is descending day by day." It notes that the red leaves on the slopes of Mount Goryu have gradually moved down to the elevation of Mount Gaki [2]. The color moves slowly down like steps on a staircase. So, why does the higher place change first? First, we must check why high places are cold.
2. Why Mountain Tops Are Cold: Height, Not Distance from the Sun
It is explained that the reason the top of a mountain is cold is not the distance from the sun [3]. Compared to the distance to the sun, the height difference of a mountain is very small. The clue lies in how air expands. Air that is lifted upward expands because the surrounding air pressure becomes lower. When it expands, the air molecules use their own energy, so the temperature drops [3]. This is an explanation found on a site for weather forecasters. This is one mechanism for how rising air cools. Actual temperatures are also affected by seasons and terrain, such as mountain slopes and valleys. The numbers we look at in the next section should be read as average guides.
3. How Much Temperature Drops Every 100 m Up: Values Differ by Source
In the Japan Meteorological Agency’s forecast terms, the "lapse rate" is defined as the rate at which temperature decreases as altitude increases. In the troposphere, it is normally explained as a drop of 0.5 to 1 degree per 100 m (about 328 feet) [4]. Numbers like "0.6°C" are average guides. The National Diet Library’s reference database lists various figures: about 0.5–0.6°C per 100 m (from an illustrated biology book), about 0.65°C (from alpine botany), and about 6.5°C per 1 km (about 0.6 miles) (from a mountain meteorology encyclopedia) [5]. These differ slightly depending on the source. The rate also changes with the season. A series of articles introducing observations from 13 temperature gauges in the Central Alps notes that in spring, the rate can exceed 0.7°C per 100 m, while in autumn, it can be around 0.4°C. The reason is the amount of water vapor in the air; from summer to autumn, the air is humid, so the lapse rate tends to be smaller [6]. This is not a rule that "autumn is always 0.4°C," but rather that "it can be that way." In this article, we use "0.4–0.6°C per 100 m" as a guide.
4. A Daily Minimum Temperature of 8°C as the Signal for Color Change
A common signal for color change is the daily minimum temperature (the lowest temperature of the day). The Japan Weather Association (tenki.jp) explains that when it falls below 8°C (46°F), coloring progresses, and they become beautifully colored about three weeks after this happens [7]. An explanation from Fukuoka Prefecture also states that leaves start changing at 8°C or below, and progress further when it drops to 5–6°C (41–43°F) [8]. Tenki.jp explains one reason is that if the daily temperature difference is large, the green pigment (chlorophyll) breaks down easily [7]. In autumn leaves, red pigment (anthocyanin) accumulates at the same time that the green pigment breaks down [9]. Both are guides and vary by tree species and region. If the signal is determined by temperature, then higher places receive the signal earlier than the foot of the mountain.
5. Converting a Height Difference into a Number of Days
Let us convert the height difference into days. In Tokyo’s daily normal minimum temperatures, the daily minimum temperature was 22.5°C (72.5°F) on September 1 and 11.7°C (53°F) on October 31, a drop of 10.8°C (19.4°F) over 61 days. This is about 0.18°C (0.32°F) per day [10]. How many days of cooling are needed for the temperature at the foot of the mountain to match the current temperature at the top? If the difference for 100 m is 0.6°C, it is about 3 days. If the autumn lapse rate is 0.4°C, it is about 2 days. If the mountain is 1,000 m (about 0.6 miles) higher, the difference is 4–6°C (7–11°F), so it is equivalent to about three weeks to a little over a month of cooling. This is my own calculation, applying the cooling speed of Tokyo’s plains directly to mountains. It is not measured mountain data. The way mountains cool in autumn is likely different from Tokyo, and the day leaves change color is not determined by temperature alone. Still, the order of magnitude of "a few days per 100 m" is a clue to imagine how fast the color descends the mountain.
6. Why the Color Change Does Not Always Descend in the Same Way
So far, we used a simple diagram: "height determines temperature, and temperature determines color." In reality, there are at least three deviations. First is the seasonal change in the lapse rate. In autumn, it can be around 0.4°C [6], so the effect of height difference on days becomes smaller (closer to the "about 2 days" mentioned in the previous section). Second, elevation’s effect on coloring changes during the season. A study using data on color change reported by citizens at over 740 locations in Japan (2015–2017) showed that the date when peak coloring begins has a linear relationship with both a warmth index and latitude/elevation. However, in places where color change is late, the effect of elevation is weaker [11]. Third is the difference within the same tree. According to Mitsutoshi Kitao of the Forestry and Forest Products Research Institute, for vivid red colors, it is better to have good sunlight and low temperatures. In the maple *Acer japonicum* (Hauchiwa-kaede), leaves on the outer side of the canopy that get sun have more anthocyanin, while leaves that do not get sun remain green [9]. There are differences in color change not just between the top and bottom of the mountain, but also within a single tree.
7. How You Can Investigate Autumn Leaf Timing Yourself
Here are two things you can check. First, open the "Past Weather Data" from the Japan Meteorological Agency and look at the daily average minimum temperature for the observation station closest to where you live [10]. When does it fall below 8°C (46°F)? Compare that date with local information on the best time to see autumn leaves. You can see if the "about three weeks" guide fits your town. Second, when color change starts, compare the leaves on the sunny side and the shaded side of the same tree in a nearby park or street tree [9]. Does the same difference appear in trees other than *Acer japonicum*? By the roadside, be careful of cars while looking from the sidewalk. You can read about the color descending the mountain with dates on the Tateyama Kurobe Alpine Route official page [1] and in the mountain hut reports on Yamakei Online [2].