Spatiotemporal variations of ultraviolet radiation over the Xizang-Tibet Plateau based on stations observations and satellite datasets

A systematic, long-term analysis of county-level UVR in Xizang is conducted by integrating satellite data from the Ozone Monitoring Instrument (OMI) and the Global Ozone Monitoring Experiment 2 (GOME-2) with ground-based observations spanning 1961–2022. The spatiotemporal characteristics and influencing factors of parameters such as UV index (UVI), UVB, and UVA are analyzed. During 2005–2022, UVA, spectral irradiances (I310:310 nm, I324:324 nm and I380:380 nm) show significant upward trends, with Sen's slope values all exceeding 0.51. The mean values of Erythemal Daily Dose, UVA, and UVB in each county of Xizang are respectively 24.85–37.79, 3.32–5.10, 903–1330 (kJ/m²), with high values distributed in the areas of Shigatse, Lhasa, and southern Shannan. The population-weighted UVI across all counties exceeds 8.65, with 84.27 % of the population classified as experiencing “Extreme” UV exposure according to the WHO's UVI classification. The percentage of UVR in surface solar radiation is higher in the west and lower in the east, peaking in summer and dipping in winter, while the UVA/UVB ratio exhibits the opposite seasonal trend, increasing exponentially from summer to winter. UVR has higher coefficient of variation in the afternoon and more fluctuating peak times in summer with a higher risk of extreme values. Spatial multiple regression analysis (p < 0.001) indicates that UVR is significantly influenced by elevation and SA (positive effects), and by ozone total column (OTC), cloud optical thickness (COT), aerosol index (AI), and latitude (negative effects), with the model performing best in autumn and for the shorter wavelength band (I305). Temporally, COT and OTC show positively synchronous variation with UVR, while SA and AI show negative. The outcomes enhance public awareness of UVR and offer valuable date for health initiatives and ecological conservation.