New Zealand’s UV levels

New Zealand’s daytime UV levels are variable across the country and could be both very high and very low, depending on the time of the year (see figure 17). In summer, daytime levels of UV are often extreme on UV indexes, a level that can damage fair skin in minutes. In winter, daytime UV levels are often low, particularly in the south of the country.

We report on data from five sites, monitored by NIWA, between September 1981 and February 2017: Leigh (Auckland region), Paraparaumu (Wellington region), Christchurch, Lauder (Otago region), and Invercargill. Over the reporting period Leigh had 74 days when UV levels were rated extreme while Invercargill had only three days. UV levels were rated as extreme in Paraparaumu, Christchurch, and Lauder for 45, 18, and 30 days, respectively.

New Zealand’s peak summer UV levels are roughly 40 percent higher than those at comparable latitudes in the Northern Hemisphere (McKenzie et al, 2006). There are three main reasons for this (McKenzie et al, 2003; 2006):

1. Earth’s orbit is elliptical, which means the Southern Hemisphere is closer to the sun during our summer.
2. The thickness of the ozone layer in the atmosphere varies seasonally (see figure 17). At mid-latitudes, such as New Zealand, it is thickest during spring and thinnest during autumn. This means the ozone layer over New Zealand thins during summer, providing less protection from UV sunlight when we are closest to the sun and the sun is highest in the sky. Moreover, our summertime ozone layer is thinner than the summertime ozone layer experienced at corresponding Northern Hemisphere latitudes.
3. The air in New Zealand tends to be clearer than that in many other locations. UV sunlight travelling through the atmosphere to Earth’s surface is scattered or absorbed by clouds and aerosols (air pollution).

Figure 17

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