Posted by: Saving Water SA (Cape Town, South Africa) – partnered with Water Rhapsody conservation systems – 12 October 2010

The arid soil of the Karoo bursts into life after the first rains

The soils in large areas of the Southern Hemisphere, including major portions of Australia, Africa and South America, have been drying up in the past decade, a group of researchers conclude in the first major study to ever examine “evapo-transpiration” on a global basis.

Most climate models have suggested that evapo-transpiration, which is the movement of water from the land to the atmosphere, would increase with global warming. The new research, published online in the journal Nature, found that’s exactly what was happening from 1982 to the late 1990s.

But in 1998, this significant increase in evapo-transpiration – which had been seven millimetres per year – slowed dramatically or stopped.

In large portions of the world, soils are now becoming drier than they used to be, releasing less water and offsetting some moisture increases elsewhere.

Due to the limited number of decades for which data are available, scientists say they can’t be sure whether this is a natural variability or part of a longer-lasting global change. But one possibility is that on a global level, a limit to the acceleration of the hydrological cycle on land has already been reached.

If that’s the case, the consequences could be serious. They could include reduced terrestrial vegetation growth, less carbon absorption, a loss of the natural cooling mechanism provided by evapo-transpiration, more heating of the land surface, more intense heat waves and a “feedback loop” that could intensify global warming.

“This is the first time we’ve ever been able to compile observations such as this for a global analysis,” said Beverly Law, a professor of global change forest science at Oregon State University. Law is co-author of the study and science director of the AmeriFlux network of 100 research sites, which is one major part of the FLUXNET synthesis that incorporates data from around the world.

“We didn’t expect to see this shift in evapo-transpiration over such a large area of the Southern Hemisphere,” Law said. “It is critical to continue such long-term observations, because until we monitor this for a longer period of time, we can’t be sure why this is occurring.” Continue reading Global soils are drying