Mountain forests are often cloudy, wet, cold and occur on isolated mountains in Africa. Rich in biodiversity, they act as water towers by capturing water from fog and clouds, providing high-quality fresh water to millions of people in the lowlands of Africa.
Over the past two decades, as much as 18% of Africa’s mountain forests have been lost due to deforestation, resulting in warming and cloud level increases twice that caused by climate change. Research has shown that air temperatures have risen by 1.4 degrees Celsius, while cloud levels have risen by 230 meters over the past twenty years.
“It has major consequences for water resources and biodiversity,” says Prof. Dirk Zeuss of the University of Marburg.
The research was published in Nature communication.
The increase in cloud level reduces water extraction
The rise of the cloud level reduces water collection because when the cloud hits the canopy, the mist (water) is deposited on the plant and land surfaces. If the cloud base is higher, this phenomenon does not occur, explains Prof. Petri Pellikka, director of Taita Research Station.
The phenomenon also requires that mountain peaks be forested, as this increases the area of land cover, and the forest stores water better in the trees and soil than in open terrain.
The study sites were in the highlands of Kenya, Tanzania, Ethiopia and South Africa. The research was one of the results of the Taita Research Station, which the University of Helsinki has maintained in southern Kenya since 2009. The University of Helsinki’s contribution to the research came from the Earth Change Observation Laboratory of the Department of Geosciences and Geography.
“Our studies in Taita Hills measured that forested mountain peaks receive 20% more water on the ground each year compared to open areas. This is due to mist deposited on the trees and dripping to the ground. In addition to the rainfall, if the clouds remain higher and do not touch the forests, this phenomenon will no longer occur,” says Pellikka.
There are still many small forested peaks in the Taita Hills. Kenya’s most important water towers are Mount Kenya, the Mau Forest, the Aberdare Mountains, Mount Elgon, the Cherangani Hills and Mount Kilimanjaro. Although Kilimanjaro is located in Tanzania, it also supplies water to the Kenyan side.
“Around Africa’s highest mountain, Mount Kilimanjaro in Tanzania, 50% of the forest has been lost since 1880,” says Dr. Andreas Hemp of the University of Bayreuth. He has been doing research in Kilimanjaro for 30 years.
Negative relationship between temperature and altitude
The study also found that due to the negative relationship between temperature and altitude, the effects of warming due to deforestation may decrease as altitude increases. Nevertheless, large-scale deforestation (i.e. a loss of tree cover of more than 70% in an area of 1 km x 1 km) can compensate for the cooling effect of altitude and similar warming can be induced at higher altitudes in African montane forests.
“The results call for urgent action because mountain deforestation, caused by cropland expansion and logging, poses a serious threat to biodiversity and ecosystem services, such as water supplies in Africa,” said Temesgen Abera, a visiting researcher at the University of Helsinki and a postdoctoral researcher in Philipps University of Marburg (Germany), funded by the Alexander von Humboldt foundation.
The study used a data-driven approach based on satellite observations, reanalysis data, as well as ensemble learning, empirical methods and independent in-situ temperature and cloud base height measurements for validation.
The research group included scientists from the University of Helsinki, the University of Marburg and the University of Bayreuth in Germany, the Finnish Meteorological Institute, Addis Ababa University in Ethiopia and Northwestern University in South Africa. The research of the ESSA project (Earth Observation and Environmental Sensing for Climate-Smart Sustainable Agropastoral Ecosystem Transformation in East Africa) was funded by the European Commission.
