Warmth index - Onryoushisuu (English spelling) index of warmth

Japanese: 温量示数 - おんりょうしすう（英語表記）index of warmth

Also called the warmth index. Invented by Tatsuo Kira in 1949, this index indicates the degree of warmth. It is a simple expression of the accumulated temperature, which is important for plant growth. It is expressed in °C per month (month degree; md). The physiological zero point of plants is set at 5 °C, and the period in which plants can grow is considered to be when the monthly mean temperature t is 5 °C or higher. The warmth index T is obtained by subtracting 5 °C from the mean temperature of each month during that period. The warmth indexes around the world are in the range of approximately 0 to 300, and some of the iso-indexes correspond well to the boundaries of actual vegetation zones. The relationship between the vegetation zones is as follows: tundra zone 0 to 15, coniferous forest zone 15 to 45, deciduous broadleaf forest zone 45 to 85, evergreen broadleaf forest zone 85 to 180, subtropical rainforest zone 180 to 240, and tropical rainforest zone 240 or higher.

Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information

Japanese:

暖かさの示数ともいう。吉良竜夫が 1949年に考案した暖かさの程度を示す示数。植物の生育にとって重要な積算温度を簡便に表わしたもの。℃・月 (month degree; m.d.) で示される。植物の生理的ゼロ点を5℃と定め，月平均気温 tが5℃以上を植物が生育できる期間とみなし，温量示数 Tは，その期間について各月の平均気温から5℃を引いた値を合計して得られる。世界各地の温量示数は，ほぼ0～300の範囲にあり，その等示数線のあるものは現実の植物帯の境界線によく一致する。植物帯との関係は，ツンドラ帯0～15，針葉樹林帯 15～45，落葉広葉樹林帯 45～85，照葉樹林帯 85～180，亜熱帯降雨林帯 180～240，熱帯降雨林帯 240以上である。

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