By Julia · weather-au.com editorial team · Published
Why Australian UV is extreme
Australia receives more ultraviolet radiation than almost anywhere else that is densely populated. Three reasons combine: the continent sits at latitudes where the summer sun is nearly overhead, the southern summer coincides with the Earth being closest to the Sun, and the air over the southern hemisphere is cleaner, with less pollution to scatter UV.
The result is a UV index that routinely reaches 12 or more in the northern half of the country in summer, levels described as extreme and reached only occasionally in Europe. A fair skin can burn in little more than ten minutes at those values.
This is not an abstraction: Australia and New Zealand have the highest skin cancer rates in the world. Sun protection here is an everyday habit rather than a holiday precaution.
What the index measures, and what it does not
The UV index is a measure of the strength of burning radiation at ground level, from 0 upwards, and it has nothing to do with heat. It peaks around solar noon and depends on the sun angle, so it is high in October long before the hottest days of January.
Because it is not heat, a cool, breezy day can carry extreme UV — the most common way people get badly burnt in Australia. A 24-degree day in Hobart in December can reach the same index as a 35-degree day in Brisbane.
Cloud is only a partial shield: thin or broken cloud cuts UV modestly, and bright cloud can even increase it at the edges by scattering. Only thick, dark cloud reduces it substantially.
The hours and places that matter
For most of the country and most of the year, the dangerous window is the three hours either side of solar noon — roughly 10 am to 3 pm, or 11 am to 4 pm where daylight saving applies. Outside it, the index falls quickly as the sun drops.
Reflection changes the picture. According to the World Health Organization, dry sand returns about 15 per cent of UV, water near the surface rather more, and fresh snow up to 80 per cent, which is why ski fields in the Victorian Alps and Kosciuszko burn faces in winter. Altitude adds roughly 10 per cent per thousand metres.
Shade works, but only when it is deep: a beach umbrella cuts direct sun and leaves the scattered component, which is why people burn under one. The practical rule remains the national one — shirt, hat, sunscreen, shade and sunglasses, in that order of effectiveness.
The scale, the alert and who measures it
The index uses the World Health Organization scale: 0 to 2 low, 3 to 5 moderate, 6 and 7 high, 8 to 10 very high, 11 and above extreme. In Australia the Bureau of Meteorology and the Cancer Council recommend sun protection whenever the index is 3 or above, and the Bureau's daily forecasts give the sun protection times during which that applies.
ARPANSA, the Australian Radiation Protection and Nuclear Safety Agency, runs a network of ground-based UV detectors in capital cities and other centres and publishes the measured index in near real time. It is a useful check on a day of changeable cloud, because it shows what actually reached the ground rather than what was forecast.
Winter in the south, all year in the north
Latitude makes a large difference within the country. In Darwin, Cairns and Townsville the index reaches 3 or more on virtually every clear day of the year, so protection is a year-round habit. In Melbourne, Hobart and the southern parts of South Australia and Western Australia, SunSmart advice is that the index usually stays below 3 for much of the period from May to mid-August, and protection is not normally needed then unless you are outdoors for long periods, at altitude or near snow.
The changeover is quick. By late August the southern states are back above 3 at midday, and by October the index in Melbourne or Adelaide is already in the very high range on clear days.
The Antarctic ozone hole, which forms each spring, mostly sits over Antarctica itself and has only a limited effect on UV over the mainland; Australia's high UV is mainly a matter of sun angle and clear air. According to the 2022 WMO/UNEP Scientific Assessment of Ozone Depletion, the ozone layer over Antarctica is expected to return to 1980 values around 2066, thanks to the Montreal Protocol.
Using the UV view on this site
Every town page carries the day’s maximum UV index, and the UV map shows the whole country at a glance, so you can see the gradient from Tasmania to the Top End on the same morning.
The useful habit is to look at the index rather than the temperature when planning an outdoor day. A forecast of 11 in Perth in November deserves the same preparation as a forecast of 11 in Cairns in January, whatever the thermometer says.
For the rest of the day, the hourly forecast shows when cloud is expected to thicken. Combined with the UV maximum, it tells you whether the shade you were counting on will actually be there.