Development of a Diagnostic Index on the Heat-wave considering Accumulative Effect of Heat-stress: the Accumulated Heat stress Index (AHI)

Heat stress accumulates in the human body when a person is exposed to thermal condition for a long time. Considering this fact, we have developed the accumulated heat stress index (AHI) in order to quantify the level of accumulated heat stress. AHI represents the heat stress accumulated 72-h period using a time-weighted function, and the accumulated heat stress is then standardized using an equiprobability transformation (from a fitted Weibull distribution to the standard normal distribution). To verify the advantage offered by the AHI, it was compared with four thermal indices – the Humidex, Heat Index, Wet-Bulb Globe Temperature, and Perceived Temperature – used by national meteorological agencies. The results indicated that the AHI provides better detection of dangerous days than the other indices. In particular, the AHI detected deaths that were caused not only by extremely hot and humid weather, but also by the persistence of moderately hot and humid weather (for example, consecutive daily maximum temperatures of 28–32°C) that the other indices failed to detect.