Temporal trends of global UV solar irradiation over the last 20 years in Valencia (eastern Spain)

The amount of solar ultraviolet radiation (UV) is a crucial parameter due to its relation to health effects, being associated with more than 90% of melanomas. But it also has significant influences on ecosystems, environments and the Earth’s atmospheric processes.

In this work, we analyze the temporal trends exhibited by the daily values of UV erythemal irradiance (UVER) and the ultraviolet Index (UVI) at noon and the daily maximum. The measurements were taken with a YES-UVB-1 radiometer located at Burjassot AtmoSpheric Station (BASS, 39º 350N, 0º 250W, 60 m.a.s.l.), covering a measurement period from 2003 to 2023. The seasonal behavior of these parameters have been characterized previously by Marín et al. (2023). The Mann-Kendall test has been now used to identify increasing or decreasing temporal trends in the data. This is a randomization vs. trend test, based on ranges. In addition to identifying the existence of a temporal trend, the Sen’s slope estimator allows to calculate the annual rate of change.  Due to the seasonality of the variables, the seasonal extension of the test was applied, using the monthly medians instead of annual values.

The UVER exhibits statistically significant increasing trends in February, May, June, July and December at 90%, 90%, 95%, 90% and 90% confidence levels, respectively. UVI at noon also shows statistically significant increasing trends in February, May, June, September and December at 90%, 99%, 99%, 80% and 80% confidence levels, respectively. Lastly, the maximum daily UVI has increased in May, June and September at 95%, 99% and 90% confidence levels. Similar results have been reported by Marson et al. (2021) at United States, attributing the increased US melanoma incidence to ground-level UV radiation intensity trends; and by Fountoulakis et al. (2021) for several months (especially in April and summer months) in three sites of Italy.

Further analysis will make use of simultaneous atmospheric composition and meteorology datasets at Valencia site to clarify the main causes for such short- and long-term trends, by use of regression analyses. It will be studied whether factors such as the decrease in total aerosol extinction and absorbing species such as black carbon could influence the trends.