Ace the Skies with the 2025 Navy FAM Ground School Weather Test – Cloud Nine Awaits!

The primary source of moisture for the majority of global precipitation is the oceans. Oceans cover about 71% of the Earth's surface and are responsible for evaporating large quantities of water due to sunlight and temperature differences. This water vapor then enters the atmosphere, where it can travel long distances before condensing into clouds and ultimately falling as precipitation in the form of rain, snow, or other forms.

While rivers, forests, and lakes also contribute to local moisture, their impact on global precipitation levels is relatively minor compared to the vast amounts of water that evaporate from the oceans. For instance, rivers and lakes can provide localized moisture but are significantly smaller reservoirs of water compared to the oceans. Similarly, forests can contribute to local humidity through transpiration, but this is a much smaller effect on the global scale. Thus, oceans serve as the dominant source of moisture for precipitation worldwide.