Reviewed by Lexie CornerAug 20 2024
International researchers from Finland, Germany, South Africa, and Ethiopia have discovered that deforestation over the past 20 years has contributed more to global warming and increased cloud cover than climate change alone. This has endangered the biodiversity and water supply of African montane forests. Their findings have been published in Nature Communications.
In Africa's montane forests, air temperature has increased by 1.4 ℃, while cloud level has risen by 230 m during the last 20 years. Image from Taita Hills in Kenya. Image Credit: Petri Pellikka
Montane forests, located on remote African mountains, are often characterized by their gloomy, wet, and cold environments. These forests are rich in biodiversity and play a crucial role as "water towers," capturing precipitation from clouds and fog and providing clean, fresh water to millions of people in Africa's lowlands.
Over the past 20 years, deforestation has destroyed up to 18 % of Africa's montane forests, leading to an increase in global temperatures and cloud cover that is twice as severe as the impact of climate change alone. Research indicates that during this period, cloud cover has risen by 230 meters, and air temperatures have increased by 1.4 °C.
It has strong consequences to the water resources and biodiversity.
Dirk Zeuss, Professor, University of Marburg
Cloud Level Rise Decreases Water Harvesting
When clouds come into contact with the forest canopy, they deposit water as fog on plant and land surfaces, enhancing water retention. However, this process doesn't occur if the cloud base is higher, as Prof. Petri Pellikka, director of Taita Research Station, explains. The phenomenon increases the surface area of land cover, and since forests store water more effectively in soil and trees than open spaces do, it is crucial for mountain tops to remain forested.
The study was conducted at sites in the highlands of Kenya, Tanzania, Ethiopia, and South Africa. It is one of the key outcomes of the Taita Research Station, which has been operated by the University of Helsinki in southern Kenya since 2009. The research received support from the Earth Change Observation Laboratory at the Department of Geosciences and Geography at the University of Helsinki.
In our studies in Taita Hills, it was measured that annually in forested mountain tops, 20 % more water was landing on the ground compared to open areas. This is due to fog deposited on the trees, which drips on the ground as droplets. This is additional to the rainfall. If the clouds remain higher and do not touch the forests, this phenomenon does not take place anymore.
Petri Pellikka, Professor and Director, Taita Research Station
The Taita Hills still contain numerous little forested mountain summits. Mount Kenya, the Mau Forest, the Aberdare Mountains, Mt. Elgon, the Cherangani Hills, and Mt. Kilimanjaro are among Kenya's most significant water towers. Even though Mt. Kilimanjaro is in Tanzania, Kenya benefits from its water supply.
“Around the highest mountain in Africa, Kilimanjaro in Tanzania, 50 % of the forest is lost since 1880,” said Dr. Andreas Hemp, University of Bayreuth, who has been conducting research on Kilimanjaro for 30 years.
Negative Relationship Between Temperature and Elevation
The study also discovered that the effects of warming brought on by deforestation can lessen with elevation because of the inverse relationship between temperature and elevation. Large-scale deforestation, however, can counteract the cooling effect of elevation and cause comparable warming at higher elevations in African montane forests (i.e., tree cover loss exceeding 70% at a 1 km × 1 km area).
The results call for urgent action as montane deforestation induced by cropland expansion and logging poses serious threats to biodiversity and ecosystem services, such as water supply in Africa.
Temesgen Abera, Visiting Scholar and Postdoctoral Researcher, University of Helsinki, Philipps University of Marburg (Germany)
The Alexander von Humboldt Foundation has funded the study.
The study employed a data-driven methodology based on satellite observations, reanalysis data, ensemble learning, empirical techniques, and independent in-situ temperature and cloud-base height measurements for validation.
The research team comprised scientists from the Finnish Meteorological Institute, Addis Abeba University in Ethiopia, North-West University in South Africa, and the Universities of Helsinki, Marburg, and Bayreuth in Germany. The study was part of the European Commission-funded ESSA project (Earth Observation and environmental sensing for climate-smart sustainable agropastoral ecosystem transformation in East Africa).
Journal Reference:
Abera, A. T., et al. (2024) Deforestation amplifies climate change effects on warming and cloud level rise in African montane forests. Nature Communications. doi.org/10.1038/s41467-024-51324-7