VOA标准英语2014--Drylands Vulnerable to Climate Change（在线收听）

Drylands Vulnerable to Climate Change

Researchers warn that the world’s drylands are being severely affected by climate change. They say that could harm the livelihoods and food security for billions of people.

Scientists describe the projected effects of climate change on drylands as alarming. Dr. Jan Ruppert is among those raising concerns.

“Drylands cover a rather big amount of the terrestrial land surface with 40-percent – a little bit more even. And they are home to approximately two-point-five-billion people of which, more or less, one-billion directly live upon rangelands or upon very basic ecosystem services, such as fodder to herd animals. They are very important for a huge amount of people,” he said.

Ruppert is a rangeland ecologist at the University of Cologne. He conducted the research with his university colleague Dr. Anja Linstadter, who led the working group.

“Drylands are not particularly deserts. Deserts are part of drylands, but not all drylands are deserts. The main definition of drylands is that they have a scarcity of water obviously. The transpiration of the water from the soil is higher than the water that comes into the system by precipitation. Actually, if you think of a savannah – that will also be a dryland in most cases,” said Ruppert.

He said that drylands historically have fared pretty well during and after droughts. But they’re more at risk now due to the effects of climate change. Human activity, such as raising livestock, can add environmental stress.

“Due to climate change the system is getting even more variable. So, the droughts will be more regular and droughts might be even more severe. And this can trigger or can push the systems above a certain tipping point and could lead to degradation. That means a change in the vegetation that cannot not be easily recovered from anymore,” he said.

Very severe droughts that usually occur only once every 100 years, may now occur much more often.

“The systems not only suffer during a drought, but also need some time to recover after a drought to be fully functional again or to be on the same production level as they had been before the drought. And now, if you can imagine, that these droughts and even these very severe droughts – centennial-scale droughts – come in more often. Then we can expect gradual losses from the systems. The systems will not be as reliable as they have been before,” he said.

A centennial-scale drought can greatly reduce the production of plant biomass from 45 to more than 70-percent in some cases. Biomass is material from living and recently living plants.

Ruppert said, “We should also consider how these numbers have been calculated and that they only represent single year drought events. And usually a drought is a multi-year phenomenon. So these numbers are actually even more likely to underestimate the reduction in production because these effects from one year to another year – if you have a multi-year drought – might even add up and lead to even more pronounced losses.”

Some drylands could gradually turn to desert – a process called desertification.

The rangeland ecologist says the type of plants on drylands matters. For instance, drylands with mostly annual plants -- which complete their lifecycle within one year -- are more severely affected during droughts. But they recover more quickly afterwards.

It’s just the opposite when perennial plants – those that come back year after year -- are in the majority. Drylands are less severely affected during droughts, but recover more slowly. Drylands are also more resistant to animal grazing during droughts when annual plants dominate.

Ruppert said that eliminating grazing is not the answer to protecting drylands during droughts and during their recovery. Instead, he says there should be better grazing management – limiting the number of livestock on the land. Also, paying herders higher prices for a time would prevent them from increasing their livestock after a drought.

The University of Cologne rangeland ecologist said protecting drylands is a food security and a livelihood issue. However, he says it does not get the attention it deserves at climate conferences. The next conference – COP 20 – opens in Lima, Peru December 1st.