Impact of heatwave definition on health effect assessment: Evidence from Thailand
P90）和 P95、 P97、 P98；持续时间包括≥ 2 d、≥ 3 d、≥ 4 d。采用随机效应meta分析定量合并60个省的结果，计算热浪对泰国人群各疾病死亡的总效应值，即以相对危险度（ RR）及其95%可信区间（ CI）的大小衡量人群对热浪敏感性的高低。 结果
P90且持续≥ 2 d），总死亡的风险增高12.8%（95% CI：10.6%~15.1%）。热浪期间人群死亡的 RR，并非完全随着热浪强度或持续时间的增加而增加。在持续≥ 2 d时，肺炎引起的死亡 RR（95% CI）为1.42（1.27~1.59）和糖尿病引起的死亡 RR（95% CI）为1.34（1.17~1.52），对以 P97定义的热浪最敏感；而总死亡（ RR：1.16，95% CI：1.13~1.20）和缺血性心脏病引起的死亡（ RR：1.35，95% CI：1.24~1.48），对以 P95定义的热浪最敏感。而以 P98定义时为例，糖尿病引起的死亡风险随着热浪持续时间的增加而增加，但总死亡和肺炎引起的死亡风险随着热浪持续时间的增加而降低。 结论
Heatwaves are a lethal natural disaster in many countries, posing a big threat to population health. However, there is no international consensus on how to properly define a heatwave.
This study aims to understand the impact of heatwave definition on the assessment of the health effects of heatwaves, and to provide evidence for the development of heatwave early warning systems.
Data on climatic variables and cause-specific deaths in 60 provinces of Thailand from 1st January 1999 to 31st December 2008 were collected. Climatic variables included daily maximum temperature, minimum temperature, mean temperature, and relative humidity. Deaths included total deaths and deaths from ischemic heart disease, pneumonia, and diabetes. Cause of death was classified according to the International Classification of Diseases, Tenth Version (ICD10). Quasi-Poisson regression combined with distributed lag non-linear model was used to assess the short-term effect of heatwaves on deaths in Thailand, and compare the risks of total and causespecific deaths under different heatwave definitions (intensity and duration). The cut-off percentiles used for heatwave definitions were the 90th, 95th, 97th, and 98th percentiles of daily mean temperature; the durations were ≥ 2 d, ≥ 3 d, and ≥ 4 d, respectively. The total effects of heatwaves on cause-specific deathsrelative risks (
RR) and corresponding 95% confidence intervals ( CI) were estimated by random-effect meta-analysis that combined the results of the 60 provinces. Results
The risks of total and cause-specific deaths increased significantly during heatwave periods, compared with non-heatwave periods. During mild heatwaves (> the 90th percentile of mean temperature and ≥ 2 d), the risk of total deaths increased by 12.8% (95%
CI:10.6%-15.1%). The RRof deaths during heatwaves did not consistently increase with the increase of heatwave intensity or duration. When the heatwave duration was ≥ 2 d, deaths due to pneumonia RR:1.42, 95% CI:1.27-1.59 and deaths due to diabetes ( RR:1.34, 95% CI:1.17-1.52) were most vulnerable to the heatwaves defined using the 97th percentile of mean temperature distribution as the threshold; total deaths ( RR:1.16, 95% CI:1.13-1.20) as well as deaths due to ischemic heart disease ( RR:1.35, 95% CI:1.24-1.48) were most vulnerable to the heatwaves defined using the 95th percentile of mean temperature distribution as the threshold. When the heatwave cut-off percentile was the 98th percentile, with the extension of heatwave duration, the risk of deaths from diabetes increased, but the risks of total deaths and deaths due to pneumonia decreased. Conclusion
This study suggests that the impact of heatwaves on death risks changes under different intensity and duration definitions. Therefore, in the development of heatwave warning systems and other heat adaptation strategies, incorporating the characteristics of heatwave vulnerability of local population and adopting an optimal local heatwave definition may more effectively protect public health in the face of heatwaves.