Evapotranspiration, the movement of water from the Earth's surface to the atmosphere, has been steadily decreasing in the southern hemisphere. What's causing this unprecedented moisture shortage, and how will it affect people down under?


Evapotranspiration comes from a couple different sources, the evaporation from land surfaces and the transpiration of water from plants. It's part of a number of larger climatic cycles, and it's crucial in the proper movement of energy and water throughout the system. At its most basic, evapotranspiration rates determine how much water plants can get, not to mention how much water is available for human consumption.

One of the suspected side effects of climate change is a shift in the water cycle, and scientists had predicted a decrease in the evapotranspiration rates. Now researchers have been able to find evidence for that shift on a global scale, as this water movement has decreased in the southern hemisphere since the last big El Niño event back in 1998. This decrease follows fifteen years of increasing evapotranspiration from 1982 to 1997. The team has found evidence for the decrease throughout the world, but the effects are strongest in Africa and Australia.


Here's the potentially good news - the decrease is real, but it's a small one. It's still possible that this is a moment of natural variability in the land water cycle, and that's maybe bolstered by the fact that the change is tied with El Niño, which is a naturally occurring event...except of course the El Niño events themselves are thought to have increased in strength and quantity over the last century because of global warming.

Either way, if the evapotranspiration rate keeps falling, it will soon threaten the survival of vulnerable ecosystems and human access to water, which is already a major problem in parts of the southern hemisphere.

[Nature]