Tropical Rainforest Climate and Canopy Structure

In the Köppen climate classification, first published by the German climatologist Wladimir Köppen in 1900 and refined through several later editions, the tropical rainforest climate is designated Af, where "A" marks a tropical climate with every month averaging above 18°C and "f" indicates that no month falls below roughly 60 millimeters of precipitation — a threshold chosen because it approximates the minimum monthly rainfall a tropical forest needs to avoid soil moisture deficit. The result is a climate with almost no true seasonality in the temperate sense: day length varies little across the year this close to the equator, temperatures stay within a narrow band typically between 25°C and 30°C, and annual rainfall commonly exceeds 2,000 millimeters, occasionally surpassing 4,000 millimeters in the wettest sites, such as parts of the western Colombian Chocó and the Cameroon coast near Mount Cameroon. The 2006 update to the Köppen-Geiger world map by Markus Kottek, Jürgen Grieser, Christoph Beck, Bruno Rudolf, and Franz Rubel, published in Meteorologische Zeitschrift, remains the standard reference cartographers and climatologists use today to delineate the Af zone's modern boundaries against satellite-era climate normals.