For day-in, day-out highs, look at the high Andes—western Bolivia, southern Peru, northern Chile and nearby Argentina. La Paz sits near 3,650 m and often sees indices in the mid-teens to around 20. The one-off research spike of about 43 at Licancabur is in that same cordillera (Cabrol et al., 2014).

How that record was taken: highest UV index ever recorded.

Altitude, latitude, and clean air stack

UV climbs about 10–12% per 1,000 m in WHO planning figures. Near the equator the noon sun stays high most of the year. Dry mountain air scatters less than lowland haze. Snow and pale rock bounce more dose back into the face—same albedo story as shade that does not cancel UV.

Other high-UV belts, not copies of La Paz

• East African highlands — Addis Ababa, Nairobi’s heights; often 13–15+.
• Mexican plateau — Mexico City (~2,250 m) regularly 14–16 in the high sun months.
• Australia — low ozone and a strong summer sun; alpine NSW and Victoria exceed the coast.
• U.S. interior West — Denver, Flagstaff, and other mile-high cities: summer 11–13 is not rare.

Use a city page or the homepage for the number you will actually get tomorrow. Geography sets the ceiling; clouds and hour of day move the reading you should pack for. Elevation math in plain language: higher air, stronger UV.