News: Heat Stress Index (HSI)

Image Source: Integrated Pub.

The Heat Stress Index (HSI) is a relative index that evaluates how people respond to variable meteorological conditions based on location and time of season. For example, the HSI accounts for the fact that a temperature of 95°F with clear skies may cause significant stress to people in Philadelphia, PA but have virtually no effect in Phoenix, AZ, where such conditions are common during the summer months. In addition, a temperature of 90°F in Philadelphia in July would create little problem, but similar temperatures in late April would induce stressful conditions.

The HSI is designed to evaluate daily relative stress values for locations throughout the United States and Canada based on deviations from average conditions during the months of May through September. The index is based on apparent temperature (a measure of temperature and humidity) and other derived meteorological variables including cloud cover, cooling degree days, and the number of consecutive days of extreme heat.

The daily HSI value is based on a scale from 0 to 10. An index value ranging from 4 to 6 indicates that the conditions at a given location are typical for that time of year. Therefore, when the index values are between 0 and 3, conditions are cooler than average and added stress due to heat will not be a factor on those days. However, index values ranging from 7 to 10 are indicative of above average heat stress conditions. There may be some discomfort associated with heat stress when the index is between 7 and 9. A HSI above 9.0 indicates severe stress, and people need to take precautions because they are not acclimated to such extreme conditions.

References
http://www.rescuedynamics.ca/articles/humidex.htm
http://www.sedhd.org/pdf/Heat%20Stress/Heat%20Index%20table.pdf
http://www.tpub.com/content/aerographer/14269/css/14269_68.htm

Source Non-Mobile: http://climate.geog.udel.edu/~jdwatts/index_web/HSI_summary.htm

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