Water scarcity is already a problem in plenty of countries, and the problem is only predicted to get worse with future population growth and rainfall patterns.

Impact models have predicted that within this century there could be 40 percent more people struggling with water shortages as a result of man-made greenhouse gas emissions than there would be if climate change was not a reality, a Potsdam Institute for Climate Impact Research news release reported.

"The steepest increase of global water scarcity might happen between [two] and [three] degrees global warming above pre-industrial levels, and this is something to be experienced within the next few decades unless emissions get cut soon," lead-author Jacob Schewe of the Potsdam Institute for Climate Impact Research said in the news release. "It is well-known that water scarcity increases, but our study is the first to quantify the relative share that climate change has in that, compared to - and adding to - the increase that is simply due to population growth."

Today about one or two out of 100 people live in a country suffering from absolute water scarcity. Climate change and population growth is expected to increase that number to 10 in 100 by the time warming rises three degrees.

Absolute water scarcity means "500 cubic meters available per year and person," the news release reported.  The global average of water consumption is about 1200 cubic meters per person per year; and the number is significantly higher in many industrialized countries.

Some of the regions at risk of a drastic decrease in water availability include: "the Mediterranean, Middle East, the southern USA, and southern China."

"Water scarcity is a major threat for human development, as for instance food security in many regions depends on irrigation - agriculture is the main water user worldwide," co-author Qiuhong Tang of the Chinese Academy of Sciences said. "Still, an increase of precipitation is also challenging - the additional water may cause water logging, flooding, and malfunctioning or failure of water-related infrastructure. So the overall risks are growing."

The research was based on a review of 11 hydrological models.

"The multi-model assessment is unique in that it gives us a good measure of uncertainties in future impacts of climate change - which in turn allows us to understand which findings are most robust," co-author Pavel Kabat of the International Institute for Applied Systems Analysis (IIASA), said. "From a risk management perspective, it becomes very clear that, if human-made climate change continues, we are putting at risk the very basis of life for millions of people, even according to the more optimistic scenarios and models."

The team plans to study how the "water requirement portfolio" will develop in specific industries as well as how technological advances will help slow the spread of water scarcity.