Has Echizen Visibility Changed Over 20 Years? Long-term Trend 2006–2025
2026-03-16
Echizen Coast in Fukui Prefecture is one of the Sea of Japan's premier dive sites. Our project has collected 20 years of data from 2006 to 2025. We examined this long-term dataset to determine whether Echizen shows a clear visibility trend.
Yearly Visibility Trend (2006–2025)
| Year | Avg Vis | YoY |
|---|---|---|
| 2006 | 8.5m | - |
| 2007 | 8.8m | +0.3m |
| 2008 | 9.2m | +0.4m |
| 2009 | 8.9m | -0.3m |
| 2010 | 9.5m | +0.6m |
| 2011 | 8.7m | -0.8m |
| 2012 | 9m | +0.3m |
| 2013 | 9.3m | +0.3m |
| 2014 | 8.4m | -0.9m |
| 2015 | 7.7m | -0.7m |
| 2016 | 10.4m | +2.7m |
| 2017 | 10.7m | +0.3m |
| 2018 | 7.1m | -3.6m |
| 2019 | 8.9m | +1.8m |
| 2020 | 10.6m | +1.7m |
| 2021 | 9.8m | -0.8m |
| 2022 | 7.9m | -1.9m |
| 2023 | 8m | +0.1m |
| 2024 | 7.5m | -0.5m |
| 2025 | 8.7m | +1.2m |
20-Year Average: 8.9m
The highest was 10.7m in 2017, lowest 7.1m in 2018. The 3.6m range shows large year-to-year variability.
Is There a Linear Trend?
The short answer: there is no clear linear trend (consistent increase or decrease) in Echizen's 20-year visibility data. Instead, a cyclical fluctuation pattern is the dominant feature.
Good Periods: 2016–2017, 2020–2021
Periods of 10m+ visibility occur in clusters. These may correlate with winter monsoon intensity and Tsushima Current activity.
Poor Periods: 2014–2015, 2018, 2022–2024
Years below 8m appear periodically. 2018's 7.1m was the 20-year low. Summer high temperatures promoting nutrient input and heavy rainfall causing river turbidity may be factors.
Sea of Japan-Specific Factors
The main factors affecting Echizen visibility differ from Pacific-side sites:
- Winter monsoon (NW wind) intensity: Strong NW winds stir the water temporarily but can promote visibility recovery afterward.
- Tsushima Current variability: Changes in warm current inflow to the Sea of Japan alter temperature, salinity, and nutrient balance.
- River input and precipitation: Fukui has heavy winter snowfall, and spring snowmelt runoff has a unique effect on visibility patterns.
Ref: JMA 'Sea of Japan Surface Temperature and Currents'
About the Data
Echizen visibility data collected from dive shop blog posts. Annual averages used. Note that sample sizes vary by year, so years with fewer observations may show higher variability.
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