On the definition of a heat wave
On the definition of a heat wave
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DOI：
10.1175/1520-0450(2001)040
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发表时间：
2001-01-01
期刊：
影响因子：
--
通讯作者：
Robinson, PJ
中科院分区：
文献类型：
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作者：
Robinson, PJ
热浪是与天气有关的死亡的主要原因。鉴于目前对全球变暖的担忧，我们有理由认为，未来气候变暖的频率、严重程度、持续时间或范围可能会增加。然而，由于缺乏对热浪的适当定义，就不可能评估过去的变化或对未来可能产生的后果。本文根据美国国家气象局（NWS）制定的热应力预报标准，提出了一套定义。当白天的高温指数和夜间的低温指数（H-i）连续超过临界值至少两天，天文台便会发出观察或警告。热指数是环境温度和湿度的组合，它近似于人体热状态的环境方面，而NWS阈值代表了生理应激开始的一般估计。这些阈值不能在全国范围内直接适用。在炎热潮湿的地区，身体、社会和文化适应将要求设置更高的阈值，以确保仅识别那些被视为压力的事件。在其他较冷的地区，即使异常炎热的事件可能被视为热浪，也可能永远达不到NWS的标准。因此，所有区域都可能出现类似数量的可感知热事件，但阈值因区域而异。分析了1951- 1990年期间毗邻美国的178个台站的每小时H-i，以确定适当的阈值标准。仅使用美国国家气象局的标准就表明，美国大部分地区每十年热浪少于三次，并采用该值作为建立适当阈值的基线。对于所有区域，测试了百分位阈值方法。利用所有可用的数据，分别为每个特定百分位数建立了白天高阈值和夜间低阈值。热浪被认为是在连续两天超过同一百分位数的白天最高和夜间最低阈值时发生的。测试了几个阈值。对于大多数南方国家来说，1%的阈值产生了合适的值。因此，热浪被定义为至少48小时内，夜间最低h -i和日间最高h -i均未低于NWS热应激阈值（分别为80华氏度和105华氏度），但年度最高h -i和最低h -i观测值均超过这些阈值的站点除外，在这种情况下，1%的值被用作热浪阈值。作为扩展，“热期”的定义类似，但发生在1%值和NWS阈值之间的事件，“暖期”发生在2%和1%值之间。同样，1%或2%的H-i值超过NWS阈值的站点给出了修改后的定义。根据这些定义对热浪发生的时间和地点进行的初步调查表明，这些定义正确地确定了重大流行病学事件。一项初步的气候对比也表明，热浪在美国南部越来越少，而在中西部和东部地区越来越频繁。
Heat waves are a major cause of weather-related deaths. With the current concern for global warming it is reasonable to suppose that they may increase in frequency, severity, duration, or areal extent in the future. However, in the absence of an adequate definition of a heat wave, it is impossible to assess either changes in the past or possible consequences for the future. A set of definitions is proposed here, based on the criteria for heat stress forecasts developed by the National Weather Service (NWS). Watches or warnings are issued when thresholds of daytime high and nighttime low heat index (H-i) values are exceeded for at least two consecutive days. The heat index is a combination of ambient temperature and humidity that approximates the environmental aspect of the thermal regime of a human body, with the NWS thresholds representing a generalized estimate of the onset of physiological stress. These thresholds cannot be applied directly nationwide. In hot and humid regions, physical, social, and cultural adaptations will require that the thresholds be set higher to ensure that only those events perceived as stressful are identified. In other, cooler, areas the NWS criteria may never be reached even though unusually hot events may be perceived as heat waves. Thus, it is likely that a similar number of perceived heat events will occur in all regions, with the thresholds varying regionally. Hourly H-i for 178 stations in the coterminous United States was analyzed for the 1951-90 period to determine appropriate threshold criteria. Use of the NWS criteria alone indicated that much of the nation had less than three heat waves per decade, and this value was adopted as the baseline against which to establish suitable thresholds. For all areas, a percentile threshold approach was tested. Using all available data, daytime high and nighttime low thresholds were established separately for each specific percentile. Heat waves were treated as occurring when conditions exceeded both the daytime high and the nighttime low thresholds of the same percentile for two consecutive days. Several thresholds were tested. For much of the South, 1% thresholds produced appropriate values. Consequently, a heat wave was defined as a period of at least 48 h during which neither the overnight low nor the daytime high H-i falls below the NWS heat stress thresholds (80 degrees and 105 degreesF, respectively), except at stations for which more than 1% of both the annual high and low H-i observations exceed these thresholds, in which case the 1% values are used as the heat wave thresholds. As an extension, "hot spells'' were similarly defined, but for events falling between the 1% values and NWS thresholds, with "warm spells'' occurring between the 2% and 1% values. Again, stations for which the 1% or 2% H-i values exceed the NWS thresholds were given modified definitions. The preliminary investigation of the timing and location of heat waves resulting from these definitions indicated that they correctly identified major epidemiological events. A tentative climatic comparison also suggests that heat waves are becoming less frequent in the southern and more frequent in the midwestern and eastern parts of the nation.