A study on soils in major parts of the Southern Hemisphere revealed that they have been getting drier in recent decades, with potential for severe consequences in those areas.
Dry areas account for a significant share of the global land surface. Findings in a study by researchers from the Oregon State University suggested that these places may be getting even drier.
The study, the first major one to investigate a phenomenon known as evapotranspiration globally, showed that significant parts of Australia, Africa, and South America have been getting drier.
The common expectation was that evapotranspiration would increase along with global warming. However, a dramatic drop or halt was observed in this research.
Soils in great portions of the Southern Hemisphere are drying out. They are giving off less water while also canceling out rises in moisture somewhere else. This can produce serious adverse effects on the environment and vegetation.
This study, which was co-authored by Professor Beverly Law, appeared in Nature.
Changes in evapotranspiration
Evapotranspiration refers to the loss of water to the atmosphere through both evaporations from land surfaces and transpiration from plants.
According to experts, around 60 percent of annual rainfall is released back to the atmosphere through evapotranspiration. The process is estimated to use over 50 percent of the solar energy that land surfaces absorb.
Evapotranspiration is a critical part of the global climate system. It links the water cycle to carbon and energy cycles.
Going by the majority of climate models, this total water loss should increase alongside global warming. This is because of an expected rise in ocean evaporation and higher overall precipitation. And that’s what researchers observed in the years from 1982 to late in the 1990s.
However, the increase in evapotranspiration was found to slow or almost stop in 1998. This finding was observed to coincide with a key El Nino incident, although this did not suggest causation.
Researchers were surprised to see a change in evapotranspiration over a vast area in the Southern Hemisphere.
A significant part of Australia and southeast Africa were among those found to be most affected. Wide portions of South America, parts of Indonesia, and central India were also impacted by critical drying.
Many of these places are naturally dry. However, some are in fact tropical rain forests.
Possible dire consequences
Researchers in this study said they were not fully sure whether the observed changes were natural or the effects of long-term global change. This was because of data being available for only a few decades.
It is feared that an acceleration limit of land’s hydrological cycle may have been reached on the global stage. If that turns out to be the case, there could be grave consequences.
Reduced growth of vegetation, increased temperature on the land surface, and lower carbon consumption are among the possible consequences. Others include loss of evapotranspiration’s intrinsic cooling mechanism and more extreme heatwaves.
A halt to the hydrological cycle’s acceleration could create a “feedback loop,” capable of worsening global warming.
Greater drought stress on vegetation would most likely be accompanied by reduced overall productivity.
A number of these concerns were observed in several sites investigated in the study. These sites around the Metolius River watershed in central Oregon’s Cascade Mountains have suffered several years of drought. They showed increased vegetative stress and have witnessed major forest fires.
Law expressed the need for long-term observations to better understand why the observed shift in evapotranspiration occurred. These would help to rule out this taking place just as a result of natural variability.