How a very dry desert “recycles” fog and dew
The ocean is not the only source of fog and dew that is vital for the many plants and animals of the Namib Desert, researchers report.
“Knowing exactly where the fog and dew are coming from will help us predict the availability of non-rainwater in the future, both in Namib and elsewhere,” says Lixin Wang, ecohydrologist and assistant professor of earth sciences at Indiana-Purdue University. University Indianapolis, who led the new study. “With this knowledge, we may be able to determine ways to harvest new water sources for potential use in water scarcity situations.”
Surprisingly, non-oceanic fog accounted for more than half of the total fog events in the Namib during the one-year period of the study. Fog derived from groundwater was the most important locally generated fog, serving as the source of more than a quarter of desert fog. Soil water, which comes from precipitation and is below the surface but located higher than the water table, also turns out to be an unexpected source of moisture.
In the desert cave, microbes feed on water, rocks, air
Arid lands, which in addition to deserts include parched but non-desert areas of the Great Plains and southwestern United States, cover about 40 percent of the earth’s surface and are home to about 2.5 billion people. With global warming, more and more areas in the United States and around the world are becoming drier and more desert-like.
“Dryland ecosystems have some of the lowest annual precipitation amounts on Earth,” says Tom Torgersen, a program manager in the Earth Sciences division of the National Science Foundation, which funded the work. “To survive, these ecosystems recycle water in the form of fog and dew. In the driest places on the planet, even seemingly minor components of the water cycle, such as fog and dew, become major and are essential to keeping the environment alive and functioning.
Much more rain once fell on the Sahara
Like other dryland ecosystems around the world, the Namib is likely to experience changes in its hydrological cycle in response to global climate change. Considering the abundance and importance of fog and dew in this desert, it provides an ideal location for studying non-stormwater.
Many parts of the Namib receive virtually no rain.
The Namib, which borders the Atlantic Ocean for 1,243 miles with temperatures ranging from less than 32 ° F (0 ° C) to 140 ° F (60 ° C), is almost completely devoid of surface water. Many parts of the Namib receive virtually no rain. Some years are without rain; other years there may only be an inch or two of rain, although some areas can receive as much as four inches. But the Namib is home to a wide variety of specially adapted organisms, such as a fog beetle. It is believed that most plants and animals in Namib derive moisture from fog or dew during periods without rain in order to survive.
Fog is made up of tiny droplets of water suspended in the air, and dew is made up of tiny droplets that form on the surface of plants, soil, and other ground objects.
Wang used analysis for stable isotopes in water – the same element with different numbers of neutrons in nuclei such as hydrogen and oxygen – to trace the origins of non-rainwater. In his future research, he plans to explore the mechanisms by which groundwater and soil water turn into fog and dew. The long-term goal is to expand this ecohydrological research beyond the Namib on a global scale.
The study appears in Scientists progress.