今日の猛暑は、熱指数を暗示するよりもずっと暑く感じられます。(Today’s heat waves feel a lot hotter than heat index implies)

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2022-08-15 カリフォルニア大学バークレー校(UCB)


The heat index is a measure of how hot it feels and rises with increasing humidity even as the temperature remains the same. If the index rises above 125-130, heat stroke is considered likely. (Graphic by Climate Central)

気象学者や国立気象局(NWS)が湿度を考慮して暑さを示すために算出する見かけの気温(暑さ指数)は、現在経験している猛暑日の体感温度を、時には華氏20度以上も過小評価していることが判明した。
暑さ指数は、湿度が高く、発汗による冷却効果が低くなると、体がどのように暑さに対処するかを示す指標であるため、この発見は、こうした熱波に苦しむ人々にとって重要な意味を持つ。

<関連情報>

慢性的に過小評価されている。拡張熱指数を用いた米国の熱波の再評価 Chronically underestimated: A reassessment of US heat waves using the extended heat index

David M. Romps and Yi-Chuan Lu
Environmental Research Letters  Accepted online: 12 August 2022
DOI:s https://doi.org/10.1088/1748-9326/ac8945

Abstract

The heat index, or apparent temperature, was never defined for extreme heat and humidity, leading to the widespread adoption of a polynomial extrapolation designed by the United States National Weather Service. Recently, however, the heat index has been extended to all combinations of temperature and humidity, presenting an opportunity to reassess past heat waves. Here, hourly temperature and humidity are used to evaluate the extended heat index over the contiguous United States during the years 1984 to 2020. It is found that the 99.9th percentile of the daily maximum heat index is highest over the Midwest. Identifying and ranking heat waves by the spatially integrated exceedance of that percentile, the Midwest once again stands out as home to the most extreme heat waves, including the top-ranked July 2011 and July 1995 heat waves. The extended heat index can also be used to evaluate the physiological stress induced by heat and humidity. It is found that the most extreme Midwest heat waves tax the cardiovascular system with a skin blood flow that is elevated severalfold, approaching the physiological limit. These effects are not captured by the National Weather Service’s polynomial extrapolation, which also underestimates the heat index by as much as 10 degrees Celsius (20 degrees Fahrenheit) during severe heat waves.

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