Wet Bulb Globe Temperature as New Heat Stress Exposure Metric

June 15, 2015

Health studies on the impact of heat waves have focused for the most part on using temperature differences and metrics such as humidity index to assign heat stress, but may not be fully accounting for the physiological response to heat. Algorithms that more accurately characterize exposure by including moisture terms to calculate Wet Bulb Globe Temperature (WBGT) could improve heat stress studies. WBGT is a heat metric that more accurately reflects heat dissipation; or the ability of the atmosphere to allow evaporation of sweat, which is the body’s response to internal temperature regulation. A study by Steven C. Sherwood and Matthew Huber suggests an unrealized lower limit for humans to physiologically adapt to prolonged heat stress from climate change. Cooling through evaporation of sweat is inefficient above wet bulb temperature (WBT) of 35 °C and leads to dangerously elevated core body temperatures. In a recently published article by Matthew Huber’s research group out of the University of New Hampshire and authored by Jonathan Buzan, thirteen different heat stress metrics are compared in the Climate Land Model (CLM4.5) in a set of routines they refer to as the “HumanIndexMod” which predicts heat stress in a variety of heat and moisture conditions. The results of the analysis found that maximum moisture conditions were linked to the most severe heat stress.

The relevance of Buzan et al., show that a common framework for calculating heat stress metrics could be teamed with local weather data sets so that “HumanIndexMod” could be used for other research applications. This work could inform heat stress environmental epidemiology studies by incorporating WBT and WBGT to improve exposure assignment in heat stress studies since it is more physiologically relevant to the body’s ability to adequately respond to adverse conditions. Models similar to HumanIndexMod have been built and linked to the CLM versions for other researchers to predict world-wide WBT exposures. A next step in the field could be to integrate other heat stress factors that WBGT takes into consideration such as wind speed and solar radiation, which is acknowledged as a limitation of Buzan’s current model. Health researchers could learn from this work and develop retrospective models to apply to mortality/morbidity datasets.

Link to Article (http://www.geosci-model-dev.net/8/151/2015/gmd-8-151-2015.html)



Buzan JR, Oleson K, Huber M. Implementation and comparison of a suite of heat stress metrics within the Community Land Model version 4.5. Geosci. Model Dev., 8, 151–170, 2015

(www.geosci-model-dev.net/8/151/2015/) doi:10.5194/gmd-8-151-2015

Steven C. Sherwood and Matthew Huber. An adaptability limit to climate change due to heat stress. Proceedings of the National Academy of Sciences, 2010. 107 (21): 9552–9555

(http://www.pnas.org/content/107/21/9552.full) doi: 10.1073/pnas.0913352107