Scientists have found that the so-called “sky-hidden rivers” in the atmosphere are the cause of dry conditions in East Africa.
The study, published in the journal Nature, shows how east-west river valleys funnel millions of tons of Indian Ocean water vapor from East Africa into the Congo rainforest, thereby reducing rainfall in East Africa.
It has always been believed that the geography of East Africa makes this region arid and drought-prone, but the exact mechanism has remained unclear to scientists until now.
The results of a new study show that east-west river valleys are a critical factor in reducing annual rainfall.
Dr. Calum Munday of the Smith School Oxford REACH program, who led the study, explains: “Usually when we think of valleys and water, we think of land-based rivers. In East Africa, deep valleys such as the Turkana Valley are driven by strong winds “And this creates invisible rivers in the sky. These invisible rivers carry millions of tons of water vapor, which is the main component of precipitation.”
The team, which had previously traveled to Kenya to measure “invisible rivers” with weather balloons, wanted to see how valleys affect Africa’s climate.
To do this, they developed a series of simulation experiments that reshaped the 6,000-kilometer East African Rift System (EARS) by gradually filling river channels.
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Study co-author Professor Richard Washington explains: “Experiments show that valleys influence climate on a continental scale. The rains cannot be uniform everywhere, and the valleys help maintain heavy rainfall in the Congo Basin, leaving East Africa vulnerable to drought.”
The team says that understanding climate trade-offs in precipitation between different regions on a continental scale can help us improve our ability to predict future precipitation patterns in Africa.
This is especially important given the political implications of climate change in Africa.
The Congo Basin is also a hotspot of biodiversity and a carbon store. The Horn of Africa, east of the valleys, is currently experiencing the longest and most severe drought on record.
Although the valleys do not affect the annual fluctuations in precipitation, Professor Washington notes: “By creating an environment in which there is very little rainfall, the valleys make East Africa more vulnerable to drought.”
On longer scales, experiments could help explain the environmental pressures faced by our early hominin ancestors millions of years ago.
The work was published in the journal Nature.