English: Clouds covered the Congo Basin on May 24, 2023, when the Moderate Resolution Imaging Spectroradiometer (MODIS) on board NASA’s Terra satellite captured this stunning true-color image. In some areas, the clouds look puffy—almost like popcorn scattered across the scene. Note, however, that clouds are completely absent over rivers and lakes in the region, including the Congo River which curves across the center of the scene.

The Congo River Basin, located along the equator in central Africa, holds a mosaic of dense rain forest, savanna, swamps, and even flooded forests, all filled with lush vegetation and considerable moisture. This area is also known as one of the cloudiest places on Earth.

Cloud formation in the Congo River Basin is in large part driven by water vapor released from trees and other plants throughout the day. Plants convert light, carbon dioxide, and water into sugar and oxygen through photosynthesis. As the plants inhale carbon dioxide, water vapor escapes, a process called transpiration. On dry, sunny days, the plants respond to the additional light by increasing photosynthesis, which releases water vapor into the atmosphere. As the warm, moist air above the plant canopy rises, it eventually begins to cool clouds form overhead.

In addition, the land itself gives off heat and moisture on warm days. This process, called evaporation, also creates clouds. The most common clouds formed in the Congo Basin are low-altitude cumulus clouds, which earned the nickname “popcorn” clouds due to their puffy appearance.

Bodies of water, on the other hand, do not change temperature as rapidly as forest and land. Water remains cooler even during full Sun exposure, typically not heating up enough to significantly warm the air above it. Because of the cooler temperatures, the air doesn’t rise, and clouds don’t form.