Ultraviolet radiation

Most skin cancers are caused by excess exposure to Ultraviolet (UV) radiation from the sun. Over-exposure to UV radiation leads to skin damage, which over time can develop into skin cancer.

Even if exposure does not cause obvious sunburn, UV radiation can cause damage to your skin which accumulates over the years. 

UV radiation, unlike heat and light cannot be seen or felt. UV radiation levels can still be very high on cool or cloudy days and skin damage can still occur. It is important not to rely on the temperature to indicate whether you need to protect yourself from the sun.

Levels of UV radiation vary during the seasons and throughout the day. In New Zealand, UV radiation levels are particularly high from September to April between hours of 10am and 4pm. It is therefore important to be SunSmart during these times.

uv graphic 2020

The Ultraviolet Index

  • UV radiation is measured by the UV index (UVI). This is a scientific tool used internationally to measure UV radiation levels. The higher the UVI number the greater the UV radiation level.
  • The UVI level is influenced by: the latitude, the amount of ozone in the atmosphere, the amount of cloud cover, reflection from surfaces such as concrete, the time of year and time of day. 
  • Whenever the UVI level is 3 or above, sun protection is required because there is a risk of skin damage.

View typical New Zealand UV radiation levels on a summer day below.  


UVI chart


Ultraviolet levels in New Zealand

Over most of New Zealand the UVI is usually 3 or above: 

  • In summer months between September and April (especially between 10am and 4pm) 
  • In winter months at high altitude and in snow. 

NIWA developed the following UVI Table to illustrate mean and peak UVI levels (taken at solar noon) throughout the year at five New Zealand centres.

Table 1:  Mean UVI Levels throughout the Year at Five New Zealand Centres

Table 2: Peak UVI Levels (Solar Noon) Throughout the Year at Five New Zealand Centres




Ultraviolet levels in New Zealand compared to overseas

During the daylight saving months (September – April), New Zealand has 40% higher peak UV radiation than places at similar latitudes in the northern hemisphere. This is primarily due to 

  • i. the elliptical path of the sun with the smallest Earth-Sun separation being in early January in the Southern Hemisphere (70%) 
  • ii. cleaner air (20%) and 
  • iii. more efficient transport of ozone in the Southern Hemisphere (10%).

In these months, (especially between 10am and 4pm), the UVI can reach 13 in the north of New Zealand, whereas during a European summer UVI levels are generally not more than about 8.

Find out the UVI in your area

To find the UVI for your area go to:

  • NIWA website - The diagrams show UV levels at specific times of the day and gives a predicted maximum UV level for sunny and cloudy skies.
  • SunSmart website – This links to the Sun Protection Alert (SPA).  The SPA is a tool that gives you the time in your city/ town when you need to protect skin not covered by clothing.

More information on UV radiation:  


A smartphone app to increase awareness of UV risks

A free smartphone app UVNZ that shows the current UV Index level, its peak value, and its progression throughout the day is now available for both Android and iPhones. The UV Index measures levels of ultraviolet radiation (UVR) from the sun. Data for the app are provided by NIWA.

Users of this app can understand more about the UV Index and what it means which helps to plan summer sun protection needs from September to April or if at high altitude in the winter. This is really helpful for outdoor workers and those who spend a lot of time outdoors.

Download the free UVNZ app from Google Play for Android phones or the App Store for iPhones.

The UV Index can also be found at www.niwa.co.nz/UV-forecasts




Last Updated: Monday 6 July, 2020