Draft:Amann’s Index of Hygrothermy

Amann's Index of Hygrothermy is an equation proposed by the Swiss botanist Jules Amann. The equation was first published in his paper L'hygrothermie du climat, facteur déterminant la répartition des espèces atlantiques (1929) and is used to quantify "hygrothermy," a measurement of climatic variably for Atlantic oceanic climates.

Usage
The Atlantic group consists of plants primarily found along Atlantic coastlines. Generally, this implies that plants within this group thrive in an oceanic climate, meaning they do best in places with lots of rain, mild winters, cool summers, and not much change in temperature throughout the year. Plants within these biogeographical groupings may have different needs when it comes to soil, like some prefer lime-rich soil, some like acidic conditions, and others aren't picky at all.

The main question explored by this equation is "What are  the  biological  factors  of  climate  and  terrain  that determine  the  distribution  of  these  Atlantic  species?" In other words, it asks whether we can use weather data to come up with a number that shows how much an area's climate is like the oceanic climate these plants need. To measure this, Amann determined that hygrothermy (a measure of moisture and warmth) increases with more rainfall and higher temperatures but decreases when the temperature changes a lot. This number tells us if these Atlantic groups could live there or not. This index aligns with other methods used to gauge oceanicity, which have been successfully employed in biogeographical studies of several different species, such as in bryophytes and lichen communities.

It is important to note that this model should not be used for very localized studies, as the survival of Atlantic plants often depends on the specific, sometimes very localized climate of their immediate environment, which can vary greatly from the general climate of the area. This explains why certain plants are found in unexpected places. Local spots with the right moisture and warmth can support plant species that require specific conditions, even if the broader region doesn't have an ideal climate. This is particularly true for small plants like mosses, which are highly sensitive to their immediate surroundings.

Formula
Hygrothermy ($$H$$) is measured by the following equation:

$$H = \frac{P \times T}{T_h - T_c}$$

Where:
 * $$P$$ = mean annual precipitation
 * $$T$$ = mean annual temperature
 * $$T_h$$ = mean temperature of the warmest month
 * $$T_c$$ = mean temperature of the coldest month