Africa’s Congo rainforest, the second-largest tropical rainforest in the world, has lost its much greenness over the past decade, a new analysis of satellite data shows.

The study demonstrates that a persistent drought in the Congo region since 2000 has affected the greenness of an increasing amount of forest area and that the browning trend has intensified over the 13 years of the study.

Scientists use the satellite-derived measurements of forest “greenness” as one indicator of a forest’s health.

Published Wednesday in the journal “Nature,” the research uses several independent satellite sensors to measure the effects of long-term drought on the Congo rainforest.

The research team was led by Dr. Liming Zhou, associate professor of atmospheric and environmental sciences with University at Albany, State University of New York.

“It’s important to understand these changes because most climate models predict tropical forests may be under stress due to increasing severe water shortages in a warmer and drier 21st century climate,” said Zhou.

Straddling the equator and covering 700,000 square miles (1,800,000 km2) in six countries, the Congo rainforest contains a quarter of the world’s remaining tropical forest.

This rainforest is inhabited by some 450 species of mammals, including forest elephants, okapi, bonobos, and all three subspecies of gorillas – the mountain gorilla, lowland gorilla, and the eastern lowland gorilla.

There are 300 reptile species, 200 amphibians, over 1,000 species of birds and more than 11,000 different plant species.

Zhou and his team say if the drying trend continues it might alter the composition and structure of the Congo rainforest, affecting its biodiversity and ability to absorb the greenhouse gas carbon dioxide.

Zhou and his team analyzed intact, forested regions in the Congo basin each year during the months of April, May and June – the first of the area’s two peak rainy and growing seasons.

The study found a gradually decreasing trend in Congo rainforest greenness, or “browning,” suggesting a slow adjustment to the long-term drying trend.
This is in contrast to the more immediate response seen in the Amazon, such as large-scale tree mortality, brought about by more episodic drought events.

The browning of the forest canopy is consistent with observed decreases in the amount of water available to plants, whether that is in the form of rainfall, water stored in the ground, water in near-surface soils, or water within the vegetation.

“Forests of the Congo basin are known to be resilient to moderate climate change because they have been exposed to dry conditions in the past few hundred years. However, the recent climate anomalies as a result of climate change and warming of the Atlantic Ocean have created severe droughts in the tropics, causing major impacts on forests.”said co-author Sassan Saatchi of NASA’s Jet Propulsion Laboratory in Pasadena, California.