综合湿度和温度影响的中国未来热浪预估

Projection of heatwaves by the combined impact of humidity and temperature in China

地面空气湿度直接影响人体驱散热负荷的效率,持续高温高湿天气将会严重影响人体健康。基于综合考虑温度和湿度协同作用的热胁迫指数--湿球黑球温度(WBGT)指数定义热浪,利用参考时期(1986-2005年)中国824个气象站点逐日平均气温和逐日相对湿度资料以及CMIP5多模式相应模拟数据,论文定量描述了未来时期(2076-2095年)不同排放情景下(RCP2.6、RCP4.5和RCP8.5)中国大陆地区可能遭遇的热浪事件的空间分布特征及其变化。研究结果表明:①最有效的减排情景(RCP2.6)和高排放情景(RCP8.5)下中国大陆地区的平均热浪日数分别是参考时期的3.4倍和6.6倍,平均热浪强度(一年内所有热浪事件中日平均WBGT指数的最大值)也相对升高了1.6℃和4.9℃,未来时期RCP8.5情景下中国东部和南部地区的最高年均热浪强度甚至将达到40℃;②虽然青藏高原地区的热浪强度等级低,但是未来时期热浪日数的增加幅度较为显著;③华南、长江中下游以及少数西南地区是综合考虑气温和湿度协同作用对人体热舒适的影响下,未来时期可能发生热浪最严重的地区,如果不考虑湿度要素的影响,那么将极有可能低估热浪在中国华南和东部等湿度较高地区的强度和影响。

Humidity is a significant factor contributing to heat stress but it is not fully considered in studies quantifying heat stress or in heat risk assessment. It is directly related to human body heat exchange and the cooccurrence of consecutive hot and humid days during a heatwave can strongly affect human health. In this study,wet-bulb globe temperature(WBGT) considering both temperature and humidity effects was utilized as a heat index to define heatwaves. Using daily mean air temperature and relative humidity data from 824 meteorological stations for the reference period(1986-2005) and the corresponding CMIP5 multi-model simulations, spatial distribution characteristics and change of heatwaves that would occur in China’s mainland were analyzed for the future period(2076-2095) under different greenhouse gas emission scenarios(RCP2.6, RCP4.5, and RCP8.5).Our analysis suggests that the average number of heatwave days in a year would be 3.4 and 6.6 times of that for the reference period under the most aggressive mitigation scenario(RCP2.6) and high emission scenario(RCP8.5), respectively. Average heatwave amplitude(as defined by the peak daily WBGT in the hottest heatwave in a year) would increase 4.9 ℃ under RCP8.5 as opposed to about 1.6 ℃ under RCP2.6. In the future period, the highest annual heatwave amplitude of eastern and southern China would reach 40 ℃ under the RCP8.5 scenario, which is higher than the optimum body core temperature(near 37 ℃). Although the Tibet Plateau has low heat amplitude, increase in the annual total heatwave days is rather significant in the future period. Heatwaves in the future would be most serious over southern China, the middle and lower reaches of the Yangtze River and parts of southwestern China considering both temperature and humidity effects on human thermal comfort. It suggests that without taking surface air humidity into consideration, there could likely be an underestimation of intensity and influences of heatwaves over areas with high humidity(such as southern and eastern China).