Ben Davis - February 2

Weather and Climate Systems

Comparison of Wet Bulb Globe Temperature in ERA5 reanalysis to the Oklahoma Mesonet

Ben Davis

Wednesday, February 2

3:00 PM

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Heat waves can have significant impacts on society through impacts on health and infrastructure. Research on heat wave predictability in the United States great plains typically relies on temperature based metrics to define and quantify heat waves. However, variables such as humidity, wind speed, and solar radiation are also important to the impact and perception of heat on humans. Therefore, organizations such as OSHA and the US Army use Wet Bulb Globe Temperature (WBGT), which has been shown to be a better predictor of heat related illness than metrics based on temperature alone. WBGT is a weighted average of air temperature, natural wet bulb temperature, and black globe temperature. Because black globe temperature and natural wet bulb temperature are not typically reported meteorological variables, they are approximated using humidity, wind speed, solar radiation, surface pressure, and air temperature. Levels of risk have been defined for WBGT, with adjustments based on activity level, clothing, and acclimation to guide decisions on what level of activity is safe given the current conditions. This presentation evaluates the ability to the ERA5 reanalysis to recreate WBGT by comparing to the Oklahoma Mesonet. The ability of ERA5 reanalysis to reasonably reconstruct observational data and climatology is important to identify methods that are appropriate for future work on the predictability of WBGT. ERA5 data is available hourly, allowing both daily and hourly climatology to be reconstructed and compared to Oklahoma Mesonet data. Further, having access to hourly reanalysis will allow future research to consider intraday variations in WBGT. Initial calculations suggest that prior to bias correction ERA5 can reconstruct WBGT to within ±2 ˚F based on Root Mean Squared Difference (RMSD), with a bias of magnitude <1 ˚F, compared to WBGT calculated from Oklahoma Mesonet observations. However, ERA5 tends to overestimate WBGT during the afternoon. Efforts to bias correct the WBGT input variables in ERA5 are ongoing. A correction applied to wind speed reduces the magnitude of the WBGT bias in ERA5 to <0.5 ˚F and provides a slight reduction to WBGT RMSD.