Water World

Turns out we still don’t like to stray too far from a refreshing drink. A global analysis finds that, despite urbanization and modern pipelines that can carry water long distances to users, over 50% of the world’s population still lives a short walk from a river, lake or pond. But people in some parts of the world tend to live closer to water than others.

“Traditionally, people have inhabited places with ready access to fresh water,” a research team led by Matti Kummu of Aalto University in Finland writes in PLoS ONE. But the rise of cities and modern wells and pipelines could mean that “the geographical distance to a freshwater source is not as vital for everyday survival as it was in the past.”

To see whether people still feel a special draw to water, the researchers gathered maps that showed population, freshwater bodies, climate and geographical boundaries. Then, they used software to calculate how far people lived from water, how climate and geography affected residence patterns, and how “water scarcity” affected how far people lived from water.

They found that population distance to water varied around the globe. In the far north and in the tropics, for example, people tend to live very close to water, in part because there are numerous lakes or rivers. In contrast, in arid areas people tend to live further from a cool drink. Overall, however, more than 50% of the world’s population lives within 3 kilometers of freshwater, and 90% within 10 kilometers, the team found.

And average population densities tend to fall the further you get from water – within 2 kilometers of water, densities are about 150 persons per square kilometer; that falls to around 50–60 persons per square kilometer at a distance of 25 kilometers from a freshwater body.

The mapping project offers some insight into future water challenges, the authors note. For example, in arid regions “where the population lives far from water bodies, adaptation based on water transport may become prohibitively expensive and unsustainable, and groundwater use and rainwater harvesting may be more effective and/or efficient.” And similar studies could help improve water access for the some 800 million people who still lack access to “improved” drinking water sources. David Malakoff | June 11, 2011

Source: Kummu M, de Moel H, Ward PJ, Varis O (2011) How Close Do We Live to Water? A Global Analysis of Population Distance to Freshwater Bodies. PLoS ONE 6(6): e20578. doi:10.1371/journal.pone.0020578

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