One of the biggest concerns about climate change is how it will affect global water supplies. Rising temperatures and changes in future precipitation patterns are expected to cause a spike in droughts around the world. Couple these factors with rising global populations and access to usable water is likely to be a major problem for many parts of the world in the coming decades.

A new analysis from the World Resources Institute (WRI) shows which regions are most vulnerable to water stress — in other words, the places where demand for water will be highest and supply lowest. The rankings, published on Wednesday, are based on climate models, global population projections and other socioeconomic predictions.

The analysis includes projections for the years 2020, 2030 and 2040 under three different scenarios: An optimistic scenario, in which we reduce our global greenhouse gas emissions and minimize climate change; a pessimistic scenario, in which we fail to mitigate climate change, population growth is high, and socioeconomic conditions get worse; and a “business-as-usual scenario,” in which greenhouse gas emissions rates continue on their current pathway, but socioeconomic conditions remain more or less the same.

Altogether, 33 countries, 14 of which lie in the Middle East or North Africa, are expected to face “extremely high” water risk by 2040. They include heavily populated areas where millions of people will be at risk, such as Algeria, Iran, Iraq, Pakistan, Syria, Greece and Spain.

Some of the 33 nations are already fairly stressed now. Others, including Botswana, Namibia and Chile,  are expected to experience dramatic increases in their water problems by 2040.

Interestingly, the projections for water stress around the world are similar no matter which trajectory is applied.] In 2040, under all three scenarios, projections for the top eight most water-stressed nations remain the same: Bahrain, Kuwait, Qatar, San Marino (a small state contained within Italy), Singapore, United Arab Emirates, Palestine and Israel.

There are two major reasons the different scenarios don’t seem to make much of a difference in the rankings, says Charles Iceland, director of the WRI’s Aqueduct project, a water risk mapping tool that was used to compile the recent rankings. One is that the projections only go to 2040, and many of the major climate consequences  aren’t expected to start taking effect until mid-century.

“The second reason is the different drivers of the models tend to cancel each other out,” Iceland says. “Basically, we found that in scenarios where there was greater climate change due to increases in greenhouse gas emissions, you’re also seeing decreasing levels of population and more efficient uses of water taking place in those scenarios.”

Many of the nations at highest risk lie in regions of the world already racked with political turmoil. In some of these nations, water shortages may have actually contributed to their current unrest, and rising water stress is likely to exacerbate any existing tensions, Iceland says.

One point that the rankings don’t address is the effectiveness of different countries at addressing their water shortage issues. Some of the nations with the highest projected water risk might actually have highly effective strategies in place for meeting their water needs, through programs such as water recycling.

Improving such programs is one key to addressing impending water stress, says Iceland, who recommends that nations start examining ways they can increase the efficiency of their food production, as well as their industrial and municipal water use. Beyond these measures, he says, the biggest priority should be to continue efforts to cut down on greenhouse gas emissions so the projections don’t become even bleaker post-2040.  

Taking the water problem seriously is a critical step toward protecting not just the well-being of individuals and families, but also of entire nations, as water availability is inextricably linked to large-scale issues such as agricultural output, food prices, public health and urbanization. And if the WRI’s projections are any indicator of what’s to come, with dozens of countries around the world facing an increasingly dry future, the conversation has never been more important.