Empirically Derived Equation from Simple Heat Index for Calculating Wet Bulb Globe Temperature: A Case Study of Thailand

Abstract

The Wet Bulb Globe Temperature (WBGT) index is a standard for assessing environmental heat stress, but the requirement of expensive instrument with specialized maintenance is limited its use. This study aims to develop the empirical equation to estimate the WBGT from Heat Index (HI) calculated from portable temperature and humidity recorder (THR), based on the data collected at seven sites covering all regions of Thailand. Comparative analysis shows that the HI values calculated from THR (HITHR) are consistent well with those measured from the thermal environmental monitor (HIQT36) as evidenced by a highly positive correlation between them (r=0.97; p<0.01; n=4,303). These results suggest high reliability of the portable THR and its acceptance to be used instead of the standard QT36 device. Based on a simple linear regression developed to estimate WBGT from the HITHR, it was found that the model accounts for at least 90% of the variance of the observed WBGT (dependent variable). In addition, validation of the model with the statistical methods shows relatively small errors of the estimated WBGT values in comparison to the observed values. With this evidence, the developed empirical regression equation can be used to estimate WBGT with high accuracy and confidence. Simple and easier to use for the practitioners who are involved in public health works at community level, a heat monitoring tool kit consisting of a THR, WBGT chart and recommended actions were further developed based on the results obtained. This tool kit is a low-cost and simple device which can be used by various community-level stakeholders to prevent and reduce heat injuries and deaths of risk groups, especially the elderly. This tool is necessary in light of anthropogenic-induced warming and Thailand’s aging society.

Development of a hot weather warning tool for heat index monitoring in Thailand

“…Additionally, we selected pilot areas based on variability and trend of Heat Index in Thailand from 1975-2017. 9 The EHTs were used at the Lao Bua Ban Health Promoting Hospital in Maha Sarakham Province, Hua Ta Lae Subdistrict Administrative Organization in Chaiyaphum Province, and Ban Ao Nam Bor School in Phuket Province as the pilot areas to evaluate its performance. The data collected in the pilot areas from March 2022 to May 2022 were used to validate the EHTs (Figure 2).…”

“…This is probably because temperature and relative humidity were elevated during the hottest month in Thailand, leading to correspondingly high HI values. 66 In addition, analysis of bias, RMSE, percentage error, and accuracy as statistical techniques to evaluate the EHT skills shows relatively small errors of HIEHT values in comparison to the HIQT36 values with the averages of bias (-0. 54) , RMSE (0.…”

“…[7][8] The Heat Index in Thailand as a whole has increased significantly by 0.53°C per decade (2.3°C for 43 years). 9 It was at the caution level (27 to <32°C) but will gradually rise to the extreme caution level (HI 32 to <41°C) in the future. Under a high emission scenario (Representative Concentration Pathway 8.5; RCP8.5) with little effort to reduce greenhouse gases emissions, heat-related deaths among the elderly are projected to increase from 3 deaths to about 58 deaths per 100,000 by 2080.…”

“…11 These findings suggest that extremely hot weather contributes to elevated cases of heat-sensitive illness and poses health risks to the public and especially the elderly, whose numbers have quickly grown due to an ageing society. 9,[12][13] Nowadays, major governmental agencies in Thailand primarily use daily measurements of maximum temperature obtained from the Thai Meteorological Department (TMD) to communicate and warn the public of extremely hot weather and heat. 14 Most provinces only have a single monitoring station which does not adequately capture the true extent of extremely hot weather and heat stress at a larger spatial scale.…”

Relative Influence of Meteorological Variables of Human Thermal Stress in Peninsular Malaysia

“…Heat stress indices are utilized to evaluate the potential effects of heat on human health and well-being. Heat Index (HI) or "Feels Like" Temperature, Wet Bulb Globe Temperature (WBGT), Humidex, Apparent Temperature (AT), Predicted Heat Strain (PHS), Universal Thermal Climate Index (UTCI), and Discomfort Index (DI) are some commonly used heat stress indices [19][20][21][22]. The information provided by these indices [19] assists individuals, communities, and industries in recognizing and mitigating the hazards associated with heat stress [18].…”