Scientists say climate change will not affect all regions of the world equally – especially when it comes to fresh water. The latest computer models indicate some places will get a lot less, while others get a lot more.

Dr. Jacob Schewe and his colleagues say that “water scarcity is a major threat for human development” if greenhouse gas emissions remain unchecked. They’ve published their findings in a special issue of the Proceedings of the National Academy of Sciences.

“The reason we’re concerned is that it’s a very important issue for a lot of people. We all depend on water for so many different purposes," he said. "And water scarcity, where it exists, really impairs many things that people do and that people live on.”

Schewe works at the Potsdam Institute for Climate Impact Research. He said the “steepest increase of global water scarcity” could happen if global warming rises two to three degrees Celsius above pre-industrial levels. That could happen, he said, in the next few decades.

“Under climate change, patterns of precipitation, patterns of temperature, of evaporation, and all these variables are going to change. And that means changes will occur in the hydrological cycles and the water cycle of the planet," he said. "And it will of course affect the availability of water around the world. So the question is in which way it will affect the water availability and will it make water even more scare in a given region, in a given place or will it lead to more water being available?”

Schewe gives some examples of where he believes the computer models are accurate.

“One example,” he said, “is the Mediterranean region. Most of the models really project a strong drying. So much less water being available. That’s mainly southern Europe, northern Africa. So these places will be affected most probably by a reduction in water availability. Another strong signal in the opposite direction is in the high northern latitudes, so, Siberia, northern Canada. These places will probably get more water.”

He said countries such as Israel, Turkey, Spain and Morocco could see as much as a 50-percent reduction from what they have now.

Findings given a medium to high confidence rating indicate that the southern United States will become drier. But there are many areas where the models disagree. And it can be difficult to develop a model that fits a particular region. One such region is West Africa’s Niger Delta.

Nevertheless, Schewe said he hopes policymakers take notice of the findings so far.

“One thing that we hope will happen is that not only national policymakers will consider them, but actually also the people who are busy with the policy negotiations about climate change mitigation. The best way to cope with it is simply not to let it happen, right? And you can still avoid a lot of these changes by simply mitigating climate change,” he said.

Agriculture is the biggest consumer of freshwater.

He said, “if you have a country that depends a lot on agriculture, where you’ve got a lot of agriculture, and you see that the water resources will go down in the future, then maybe now you still have some time to find the resources, find the funding, develop the technologies or buy the technologies and to use the water more efficiently. And also, to put regulations in place to avoid overuse of the resources -- and to distribute it evenly across the different users.”

Schewe is calling on more researchers to develop climate change models.

Co-author, Dr. Pavel Kabat – of the International Institute for Applied Systems Analysis – said if human-made climate change continues the very basis of life for millions of people will be put at risk – even under the more optimistic scenarios and models.