Although water scarcity is already a problem in many countries today due to factors like population growth, the effects of global warming could put millions more people at risk of absolute water scarcity, according to a new study from the Potsdam Institute for Climate Impact Research.
The study, published Monday in a special issue of the journal Proceedings of the National Academy of Sciences, found that water resources will be affected by changes in rainfall and evaporation due to climate change, putting 40 percent more people at risk of absolute water scarcity.
"We conclude that the combination of unmitigated climate change and further population growth will expose a significant fraction of the world population to chronic or absolute water scarcity," the study says.
Now, between one and two people out of 100 live in countries with absolute water scarcity, which is defined as less than 500 cubic meters of water available per year and per person, according to the study. On average, each person consumes about 1,200 cubic meters of water each year. But population growth combined with the effects of global warming could bring the ratio of people living in countries with absolute water scarcity up to about 10 in 100 people.
"The quantities that most humans need for drinking and sanitation are relatively small, and the fact that these basic needs are not satisfied for many people today is primarily a matter of access to, and quality of, available water resources," the study says.
Unless greenhouse gas emissions get cut soon, this situation could become reality "within the next few decades," Jacob Schewe, the study's lead author, said in a statement.
But because climate change does not have the same effect across or even within certain countries, some areas will be hit harder than others. The Mediterranean, the Middle East, the southern United States and southern China, for example, could see a "pronounced decrease of available water," while southern India, western China, and parts of eastern Africa could see an increase.
To account for the uncertainty of climate change – the magnitude of its effects and water scarcity changes at a regional level – the researchers used 11 hydrological models, produced by five different global climate models. The results in the study represent the multiple-model average.
"The purpose is to explore the associated uncertainties and to synthesize the current state of knowledge about the impact of climate change on renewable water resources at the global scale," the study says.
While the average level of water scarcity resulting from population change alone is amplified by 40 percent with climate change, some models suggested the amplification could be as high as 100 percent.
"This dwindling per-capita water availability is likely to pose major challenges for societies to adapt their water use and management," the study says.