Rapid urban growth and climate change will leave more than 1 billion urban dwellers with a water shortage by 2050, according to a study released last week.

Published in the Proceedings of the National Academy of Sciences, the study shows urban growth rates alone leaving 993 million city residents living on less than 100 liters of water a day. The effects of climate change add 100 million people to that toll. Rob McDonald, lead author of the study, said these numbers reflect current trends and are by no means definitive.

"Fast urban growth and climate change pose a challenge," said McDonald, a scientist with the Nature Conservancy. "It's a challenge that can be met and has to be met."

The 100-liter-per-day benchmark comes from the World Health Organization and the U.S. Agency for International Development. Both recommend it as the minimum amount for consumption in normal uses like bathing, drinking and cooking. In contrast, the average American uses 376 liters a day, although that number varies per region.

For the study, McDonald and six other scientists used a projected global population of 9 billion by 2050. That paints a picture of a world where one of every nine people lacks a reliable water supply. Currently, about 150 million people worldwide get by on less than 100 liters of water every day. The U.S. Census Bureau estimates the present world population at 6.9 billion.

Between now and 2050, the study projects the world will add 3 billion people in cities, most of them in developing areas in India, West Africa and China. That's roughly the equivalent of adding a city the size of Washington, D.C., to the world every week, McDonald said.

Much of this urban growth will occur in areas with seasonal water shortages. The study projects 3.1 billion people will be dealing with seasonal water shortages by 2050.

Shifting water away from agriculture?
McDonald identifies three elements essential to urban areas providing water to people. First, there has to be enough water nearby for a city to tap into. Second, an infrastructure needs to be developed that can bring that water to its people. Finally, that water has to be clean enough to drink. His study focuses on the first element, water availability.

While a shifting climate will change different environments in different ways, it will ultimately leave more people without water than before, according to the study.

"Some cities are going to get wetter, and some will get drier," McDonald said, "but [climate change] puts 100 million more in water-stressed areas."

Since most of the projected urban growth will happen in seasonally water-stressed areas, there's a wider range of solutions for the problem than there would be in dry areas like deserts, McDonald said.

Agriculture, the world's biggest water consumer, is also one of its the biggest wasters. The report recommends improving the industry's efficiency and cites previously successful approaches. One, in South Africa, had farmers remove plantations of non-native trees that require a lot of water to survive.

The report is a part of a series of studies from the National Center for Ecological Analysis and Synthesis examining the effects of urban growth. Its funding came from the National Science Foundation and the Nature Conservancy.

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500