Taiwan UV Index Levels and Sun Protection Guide

UVI Tiers and Protective Measures

The Central Weather Administration (CWA, 中央氣象署) categorizes Ultraviolet Index (UVI) measurements into five standardized exposure tiers, tracking potential sunburn risks within specific exposure timeframes:

Tier Classification	UVI Index	CWA Explanation and Sunburn Limits	WHO Summary Recommendations
Low (Green)	0 to 2 (0-2; less than or equal to 2)	Index less than or equal to 2 is Low.	Can safely stay outdoors.
Moderate (Yellow)	3 to 5 (3-5)	Index 3 to 5 is Moderate.	3 to 7: Seek shade during midday; put on clothing, sunscreen, and hat.
High (Orange)	6 to 7 (6-7)	Index 6 to 7 is High; sunburn risk within 30 minutes; hats/parasols, sunscreen, sunglasses, shade.	Same as above (3 to 7).
Very High (Red)	8 to 10 (8-10)	Index 8 to 10 is Very High; sunburn within 20 minutes; hats/parasols, sunscreen, sunglasses, shade, long sleeves, avoid sun from 10 to 14 (10 至 14 時最好不在烈日下活動).	8 and above: Avoid outdoor exposure at midday; seek shade, clothing, sunscreen, and hat mandatory.
Extreme (Purple)	11 and above (11+; greater than or equal to 11)	Index greater than or equal to 11 is Extreme; sunburn within 15 minutes; same precautions as Very High.	WHO merges 11+ into 8 and above without a separate category.

Note: WHO defines three bands (0-2, 3-7, 8 and above); five tier names are detailed in CWA guidance. CWA charts (PDF page 3) list sunburn times: High within 30 minutes, Very High within 20 minutes, Extreme within 15 minutes, with Low and Moderate blank.

CWA Protective Precautions

The Central Weather Administration outlines five core protective measures for outdoor safety:

Pay close attention to daily Ultraviolet Index (UVI) forecasts before outdoor activities.
Exercise heightened vigilance in alpine elevations, coastal beaches, and snowfields, where UV reflection multiplies exposure.
Adopt effective physical barriers, including long-sleeved clothing, wide-brim hats, UV parasols, and sunglasses.
Reapply appropriate broad-spectrum sunscreen lotion continuously throughout outdoor exposure.
Avoid direct exposure under intense sunlight between 10:00 AM and 2:00 PM (10:00 to 14:00; 10 至 14 時; 10 時至下午 2 時).

How to Read Observation Station Values

CWA defines UVI as the intensity of UV radiation reaching unit ground area; higher values indicate stronger accumulated radiation over time. Forecasts reflect peak midday values rather than full-day averages.

Seasonal Variance: In the Northern Hemisphere, UV radiation peaks from June to August (6 月到 8 月) and drops to annual lows from December to February (12 月到 2 月); areas closer to the equator experience higher baseline indices. Cloud cover, ozone thickness, and air pollution modify intensity.
Cloud Cover and Weather Conditions: In CWA reference tables, daytime summer rainfall and overcast skies generally record Low index ratings, cloudy skies yield Moderate readings, broken clouds register High, and clear cloudless skies produce Very High to Extreme levels. Spring and autumn drop 1 to 2 indices, and winter drops one tier.
Computational Standard: CWA monitors erythemal UV irradiance up to 400 nm wavelengths, weighting spectral bands against the standard erythemal action spectrum to calculate total UV intensity, multiplied by 0.04 (each UVI unit equals 25 mW/m²); for example, peak midday radiation of 200 mW/m² converts to UVI 8.
Monitoring Station Datasets: Under CWA Open Data Catalog O-A0005-001 (September 2023 version; 2023/09/15), automated stations (21 stations through Year 2021; 110 年共 21 個站) update daily maximum values around 2:00 PM, with -999 representing missing observation data.

CWA UV observation maps feature real-time observations and today maximum tabs. Blank displays mean data has not yet arrived rather than zero risk. Day protection depends on midday numbers.

Three Steps Before Heading Outdoors

Follow a practical 3-step routine before leaving home:

Check daily UVI forecasts or observe regional monitoring station readings to identify exposure risk tiers.
When UVI reaches 3 or higher, prepare hats, UV parasols, or long sleeves, reapplying sunscreen according to CWA guidance; avoid direct sun between 10:00 AM and 2:00 PM (10:00 to 14:00).
Exercise extra caution in high mountains or beach environments; check numerical indices even on cloudy summer days rather than judging UV risks purely by sunlight visibility.

Review real-time data using our Taiwan UV index tool and local weather forecasts in Taiwan weather today. Protect household systems with guides on HVAC electrical overload prevention, summer cooling in air conditioner maintenance, and utility safety in seasonal utility safety checklists.

Frequently Asked Questions

Should Sunscreen Be Applied at UVI 3?

Yes. The World Health Organization (WHO) and CWA advise sun protection whenever the UV Index reaches 3 (Moderate) or higher.

Is Sun Protection Needed on Overcast Days?

Yes. Up to 80% of ultraviolet radiation penetrates light clouds; overcast summer skies frequently register Moderate or High UVI ratings.

Why Do Station Observations Diverge from Forecasts or Appear Blank?

Forecasts model peak regional clear-sky potentials, whereas station sensors log localized ground measurements influenced by passing cloud cover. Sensor maintenance or missing data shows -999 or temporary blank values.

Last updated: 2026-10-28. Public data compiled for general reference; verify latest updates at official CWA portals.

Sources

Central Weather Administration: Ultraviolet Knowledge (MFC_uviknowledge.pdf): UVI definitions, calculations, WHO thresholds, sunburn times (PDF page 3 chart), 5 precautions, seasonal/cloud factors.
Central Weather Administration: Open Data Catalog O-A0005-001 (Updated September 15, 2023; 2023/09/15): 21 stations, updated around 2:00 PM daily, -999 missing data indicator.
Central Weather Administration: Real-Time Ultraviolet Observation Map: Real-time and daily maximum observation tabs, missing data indicators, 5-tier classification.
World Health Organization (WHO): Radiation and the Ultraviolet (UV) Index: 0-2, 3-7, 8 and above sun protection guidelines.