UV Index in Koshu, Japan

Last updated: July 2, 2025

In Koshu, Japan, understanding the UV Index is crucial for maintaining skin health and preventing unwanted sunburns. The UV levels can fluctuate significantly throughout the day, peaking at 12 between 11 AM and 1 PM, making it essential to be sun-smart during these hours. Residents and visitors should be particularly cautious, as the Dfb climate offers both warm summers and cold winters, leading to a surprising variety of UV exposure risks. By keeping an eye on the UV Index, you can enjoy the beautiful outdoors while protecting your skin from harmful rays.

Hourly UV Index in Koshu

As the sun rises, the UV Index begins its ascent, reaching maximum levels early in the day. At 07:00, it starts at a mild 2, but by 08:00, it spikes to 5. The peak occurs between 11:00 and 12:00, when the index hits its highest at 12, indicating a significant potential for skin damage without protection. The afternoon sees a gradual decline; it drops to 8 by 14:00 and continues to lessen, settling at 6 by 15:00, before tapering off to 3 at 16:00, and then further to 1 by 18:00. As the day winds down, the UV Index finally drops to a safe 0 by 19:00, reminding us of the importance of sun protection during those peak hours!

Average solar exposure data for the current time of the year. Actual values may vary and depend on many factors, such as cloud cover, vegetation cover, surface type, etc.
Time	UVI	Category	Time to Burn
07:00	2	low	45 min
08:00	5	moderate	30 min
09:00	7	high	25 min
10:00	10	very high	15 min
11:00	12	extreme	10 min
12:00	12	extreme	10 min
13:00	11	extreme	10 min
14:00	8	very high	15 min
15:00	6	high	25 min
16:00	3	moderate	30 min
17:00	2	low	45 min
18:00	1	low	45 min
19:00	0	low	45 min

Monthly UV Index Trends in Koshu

Throughout the year, the UV Index demonstrates notable seasonal changes, with the most intense exposure occurring from April to August. During these months, the UV Index reaches extreme levels (10-12), significantly reducing the burn time to just 10 minutes. March and September also pose risks with very high levels (8-10), allowing for a burn time of only 15 minutes. Consequently, February and October present high levels (6-7), where protective measures are still advised with adjusted burn times of 25 minutes. Residents and visitors should exercise caution and protect their skin, especially during the high-risk months of April through August, by using sunscreen, wearing protective clothing, and limiting sun exposure during peak hours.

Monthly Maximum UV Index for Koshu, Japan

The monthly maximum UV Index (UVI) represents the highest UV radiation level recorded each month in Koshu. It measures the strength of ultraviolet radiation from the sun and helps assess the risk of sunburn and UV-related health issues.

Data source: Statistical UV Index data for Koshu, based on information from the Copernicus Climate Change Service.

UV Risk Categories

Extreme (11+): Avoid the sun, stay in shade.
Very High (8-10): Limit sun exposure.
High (6-7): Use SPF 30+ and protective clothing.
Moderate (3-5): Midday shade recommended.
Low (0-2): No protection needed.

Compare Koshu UV Index with Other Japan Cities

The table above highlights how UV exposure in Koshu compares to other major locations across Japan. This comparison helps travelers and residents better understand regional sun intensity and plan outdoor activities with sun safety in mind.

Koshu's solar exposure compared to other cities in Japan. Generated using Copernicus Atmosphere Monitoring Service information.
	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Sapporo UVI	2	3	6	7	9	9	9	10	8	5	3	2
Yokohama UVI	3	5	8	9	11	11	11	11	10	7	5	4
Tokyo UVI	3	5	8	9	11	11	11	11	10	7	5	4
Nagoya UVI	4	6	8	10	11	11	11	11	10	7	5	3
Osaka UVI	4	6	8	11	11	11	12	11	10	7	5	3
Koshu	4	6	8	10	11	11	12	11	10	7	5	4