• Researchers at the National Institute of Water and Atmospheric Research (NIWA) have discovered that
Cuzco, Peru is the site where the highest levels of ultraviolet (UV) rays occur on Earth.
• The strength of UV radiation is measured in terms of the UV index. Typically, on this scale, UVI levels
over 10 are considered dangerous to even somewhat prolonged exposure. In an area with a UVI rate of 10, a
fair-complexioned person will typically begin to experience sunburn after half an hour.
Cuzco has a measured peak UVI of 25, considered extremely hazardous to exposed skin.
Fig. 5: each “pixel” represents a different measured zone. The zone centered over Cuzco (as
indicated on the map) was the only one to top a peak UVI index of 22.
Several factors contribute to this:
- Cuzco’s elevation, at roughly 2.7 km above sea level. Air scatters and absorbs UV rays; the higher up, the less air to absorb UV.
- Cloud cover. Clouds absorb, on average, 30% of UV rays. Cuzco, particularly during its dry season, has far fewer clouds, and they contribute to only a rough 9% absorption rate.
- Ozone depletion. Ozone is a great absorber of ozone. It’s depletion has affected Cuzco, especially during the summer months when moving thinner patches of the ozone layer center over Peru.
- Peru has the third-highest skin cancer rate in South America; the rate in Cuzco is roughly 8% higher than the rest of the country. Exposure to UV rays is a significant contributor to the formation of skin cancer.
(Source: Liley, J. Ben and Richard McKenzie. “Where on Earth Has the Highest UV?” UV Radiation and Its Effects:
Update. April 2006. NIWA, Hamilton, New Zealand. Source: Environmental Protection Agency. This information can be found at http://www.epa.gov/sunwise/uvindex.html.)