Britannica
Sources used in this answer
How does precipitation seasonality distinguish Af, Am, and Aw climates?
Created from Britannica articles
using AI.
AI can make mistakes, so verify using Britannica articles.
Köppen climate classification
The major climatic types are based on patterns of average precipitation, average temperature, and natural vegetation. This map depicts the world distribution of climate types based on the classification originally invented by Wladimir Köppen in 1900.
In the Köppen climate classification system, the tropical (Type A) climates—Af, Am, and Aw—are primarily distinguished by the duration and intensity of their seasonal precipitation patterns.1
- Wet equatorial climate (Af): This climate is characterized by high rainfall that is distributed fairly evenly throughout the year, with no pronounced dry season.2
- Tropical monsoon and trade-wind littoral climate (Am): These regions experience high annual precipitation, often exceeding that of Af climates, but they are distinguished by a short, distinct dry season, typically occurring during the low-sun ("winter") period.3
- Tropical wet-dry climate (Aw): This climate features a more significant seasonal contrast, with a clear division between a wet season (occurring during the high-sun or "summer" period) and a longer, more pronounced dry season. As one moves poleward through these regions, the dry season becomes progressively longer.4
These variations are largely driven by the seasonal migration of the intertropical convergence zone and fluctuations in trade winds or monsoon circulations.413