Feasibility of Relative Strain Index (RSI) for the Assessment of Heat Stress in Outdoor Environments: Case Study in Three Different Climates of Iran

Objectives: Different indices are used to evaluate heat stress in outdoor environments. This study was aimed at examining the applicability of the Relative Strain Index (RSI) to the assessment of heat stress in several climates of Iran. Methods: Based on the Köppen classification, three different climates were studied. Arak, Bandar Abbas, and Sari were selected as representative of semi-arid and cold climates, hot and dry, and Mediterranean, respectively. The data recorded by the meteorological organization, including air temperature, relative humidity and air velocity were surveyed during 15-year period in three different climates. The RSI index was calculated by the formula. Also, the Wet Bulb Globe Temperature (WBGT) index was computed using a model presented by the Australian Bureau of Meteorology (ABM). Data were analyzed using SPSS v.22, descriptive statistics, Pearson correlation coefficient, and linear regression. Results: The mean RSI index in summer of the 15 years in Arak was 0.033 ± 0.33, in Bandar Abbas 0.54 ± 0.6 and for Sari was 0.17 ± 0.05. A high correlation was found between environmental variables and RSI index in three different climates. As well, there was a positive and significant correlation between both RSI and WBGT indices in three different climates (R2>0.96). Conclusion: The RSI index is a simple and empirical index and can be used for the evaluation of heat stress along with other indices. The index estimates the situation more than expected to be stressful in warm and dry conditions. So, it is not a useful index for hot and dry climates such as Bandar Abbas.

Do Biometeorological Indices Improve Modeling Outcomes of Heat-Related Mortality?

Various biometeorological indices and temperature measures have been used to assess heat-related health risks. Composite indices are expected to assess human comfort more accurately than do temperature measures alone. The performances of several common biometeorological indices and temperature measures in evaluating the heat-related mortality in Brisbane, Australia—a city with a subtropical climate—were compared. Daily counts of deaths from organic causes [International Statistical Classification of Diseases and Related Health Problems, 9th Revision, (ICD9) codes 001–799 and ICD, 10th Revision, (ICD10) codes A00–R99] during the period from 1 January 1996 to 30 November 2004 were used. Several composite biometeorological indices were considered, such as apparent temperature, relative strain index, Thom discomfort index, the humidex, and wet-bulb globe temperature. Hot days were defined as those days falling into the 95th percentile of each thermal stress indicator. Case-crossover analysis was applied to estimate the relationship between exposure to heat and mortality. The performances of various biometeorological indices and temperature measures were compared using the jackknife resampling method. The results show that more deaths were likely to occur on hot days than on other (i.e., control) days regardless of the temperature measure or biometeorological index that is considered. The magnitude of the odds ratios varied with temperature indicators, between 1.08 [95% confidence interval (CI): 1.02–1.14] and 1.41 (95% CI: 1.22–1.64) after adjusting for air pollutants (particulate matter with aerodynamic diameter less than 10 μm and ozone). Average temperature performed similarly to the composite indices, but minimum and maximum temperatures performed relatively poorer. Thus, average temperature may be suitable for the development of weather–health warning systems if the findings presented herein are confirmed in different locations.