Assessing Long-Term Trends in Heat Stress in Murcia using the Wet Bulb Globe Temperature Index over the ERA5 Period

The increase in temperatures over recent decades during the warm season in the Iberian Peninsula, and more generally across most continental mid-latitude regions, constitutes one of the clearest signals of climate change. This trend, together with an atmosphere capable of holding higher amounts of water vapor, reduces thermal comfort and has significant socio-economic impacts, particularly on outdoor occupational activities.

 

The Wet Bulb Globe Temperature (WBGT) index, which combines temperature, radiation, humidity, and wind, is a widely used metric for assessing occupational heat stress. Although the index can be measured directly using thermal sensors, such instruments are rarely used for continuous monitoring, and long-term observational records suitable for climate studies are scarce. However, several methodologies allow its estimation from indirect measurements of the aforementioned variables, though these approaches have not been extensively validated against long-term direct observations.

 

In this study, we present a validation of the WBGT calculation method proposed by Liljegren et al. (2008), using meteorological data from the AEMET station in Murcia. The validation compares an indirectly derived WBGT series with direct observations over a two-year period. Once validated, the method is applied to ERA5 reanalysis outputs to generate hourly WBGT data, which are subsequently post-processed to correct systematic errors. The resulting series reveals positive trends in the index, indicating an increase in occupational heat stress in recent decades.