Recently, increasing urban temperatures due to the Urban Heat Island (UHI) effect and Global Warming (GW) have been remarkable in some Japanese metropolises. The UHI effect and GW not only cause temperatures to rise, they also have other diverse impacts on urban dwellers. Therefore, it is important to understand the effect of temperature increase on urban dwellers to take action for preventing the occurrence of adverse impact. In this regard, the authors have shown the overall perspective of the effect of temperature change on urban dwellers by relation diagram, and evaluated the influence on energy, resources, health, air pollution etc. as much as possible quantitatively.
This paper aims to comprehensively and quantitatively evaluate the impact of urban outdoor temperature change on human health in Osaka Prefecture, based on the data accumulated by the authors and the results of past researches, conducted an annual evaluation from fatal severe to relatively mild impact. Specifically, based on the concept of endpoint-type life cycle impact assessment method, human health impact due to various diseases was integrally evaluated using DALY (disability-adjusted life year). The evaluated diseases were heat / cold stress and hyperthermia as fatal severe effect, infections such as Herpangina as relatively severe effect, sleep disturbance, fatigue and mild heatstroke as a relatively mild effect. The time range of the evaluation was from 1967 to 1977 (1970s) as the base period, from 1987 to 1997 (1990s), further from 2007 to 2017 (2010s) over the past 40 years.
The results of this research are described below.
1) With respect to the disability weight that is indispensable for the evaluation of DALY, the value of mild heatstroke was determined by questionnaire survey for 70 physicians with reference to Müller-Wenk's method. The average value was 0.081 for Grade I, 0.237 for Grade II and 0.463 for Grade III.
2) The average comprehensive value of DALY for annual evaluation was particularly remarkable increase in the period from the 1990s to the 2010s, it was about four times as much as the change from the 1970s to the 1990s.
3) The maximum comprehensive value of DALY throughout each period was recorded in 1994, this indicate slightly different from secular trend of average value and the influence of sudden and intense heat was strong.
4) The minimum comprehensive value in the 2010s was almost the same as the average value of the 1970s, this showed that DALY increased steadily and extremely low situation did not occur.
5) The comprehensive value of DALY increased from May to October due to the temperature change of 40 years but decreased from November to April. In other words, urban temperature change had a negative impact on health from the early summer to the early autumn, while a positive impact from late autumn to spring.
6) The largest increase of DALY was seen in August, especially deterioration in sleep disturbance, fatigue, death by heat stress and death by hyperthermia showed large impact. On the other hands, the largest decrease was seen in February, mitigation in fatigue and cold stress showed large impact. The annual total value of DALY increased by 2,854 [DALY].
7) The influence of sleep disturbance and fatigue had a large impact on the change in DALY. Although the disability weight and the disease period are small for these disease, these influences are indispensable to evaluate the entire of human health from the macro viewpoint of urban area.