Nonlinear UV Radiation Gradients Reveal Microclimatic Control in High-Andean Elevations

Extreme ultraviolet radiation (UVR) remains an underestimated public-health threat in high-Andean environments, where standard ultraviolet index (UVI) scales fail to capture actual exposure risks. This study presents the first high-frequency, year-round characterization of UVI dynamics and their environmental drivers across the altitudinal gradient of Puno, Peru (3810–4134 m a.s.l.). Between July 2024 and July 2025, 140 572 measurements were recorded using a Pasco e789 sensor. Statistical analyses (one-/two-way ANOVA, Tukey, Pearson correlations, PCA) revealed nonlinear UVI–altitude responses, challenging the classical 8–10% increase per 1000 m. The highest UVI reached 43.12 at 3810 m in December 2024 well above global extreme-risk thresholds. Seasonal maxima (UVI > 30) concentrated between November 2024 and March 2025, while winter minima dropped to UVI 5–6. Temperature showed a positive association with UVI (r = 0.54), humidity increased UVI at higher elevations (r = 0.56), and wind reduced UVI at lower sites (r = -0.38). Overall, these findings demonstrate strong microclimatic modulation of UVR and underscore the need to adapt international photoprotection guidelines to the chronic extreme-radiation exposure experienced by Andean populations. Temperature showed a direct correlation with UVI up to r = 0.54. At 4134 m a.s.l., humidity increased UVI with a correlation of r = 0.56. At 3810 m a.s.l., wind reduced UVI showing a correlation of r = -0.38.