Increasing solar ultraviolet radiation (UVR) has the potential to adversely affect humans, life on Earth and the environment, impacting both human health and the sustainability of ecosystem. Precise measurements over several decades and thorough data analyses are crucial for identifying and understanding changes in ground-level solar UVR.
For the locations Dortmund in Germany and Uccle in Belgium, we processed and analysed spectrally resolved data on solar UVR from UV monitoring stations. Influencing factors such as total column ozone, global radiation and sunshine duration were considered in analysis and discussion. The differences in annual UV dose between the two locations are consistent with the variations in global radiation. A detailed analysis of ozone influence in Dortmund reveals the impact of the normal ozone annual course and low-ozone events on the UV data separately.
An advanced linear model was developed and applied for the trend analysis. The results show a statistically significant increase in the monthly mean standard erythemal dose and UV Index values from 1997 to 2022 in both Dortmund (SED, 4.9% per decade, UVI, 3.2% per decade) and Uccle (SED: 7.5% per decade, UVI: 5.8% per decade). In Dortmund, the global radiation increases equally to the SED and UVI data. Sunshine duration, which primarily depends on the change in cloud cover, increases by 11.3 % per decade, roughly twice as much as global radiation. Total column ozone shows a slight but statistically significant decrease in summer months (0.9% per decade).
The overall results suggest that the changes in monthly UVI and SED mean values are primarily driven by changes in global radiation, which in turn are primarily caused by changes of sunshine duration. A decreasing summer total column ozone may also influence UVI and SED changes; but on a minor level.