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Population Growth and Climate Change Threaten Urban Freshwater Provision
May 6, 2011 By Emanuel FeldBy 2050, more than one billion urban dwellers could face perennial freshwater shortages if major improvements are not made to water management practices and infrastructure, according to a recent study published in the journal PNAS, “Urban Growth, Climate change, and Freshwater Availability.” These challenges will arise as hydrologic changes due to climate change compound “an unprecedented wave of urban growth,” with nearly three billion additional urban residents forecast by 2050. “It is a solvable problem,” the study argues, “but one that will take money, time, political will, and effective governance.”
Using demographic data from the Earth Institute at Columbia University, as well as a variety of climate and city-level demographic scenarios, the researchers estimate per-capita water availability for cities in the developing world, where urban growth will be most rapid. They advise, however, that their findings should be taken as conservative estimates, since the study assumes cities can use all nearby water and does not account for key challenges relating to water quality and delivery to urban centers.
In 2000, 150 million people in developing countries lived in urban areas that could not support their own water requirements (i.e. less than 100 liters available per person per day). By 2050, according to the study, urban population growth alone could bring this figure to 993 million and more than three billion could face intermittent shortages at least one month out of the year. When the researchers expanded the area on which cities can draw upon to include a 100 km buffer zone, these values drop to 145 million and 1.3 billion, respectively.
However, once climate and land use change are included in the models, the aggregate number of people facing perennial shortages rises a further 100 million, if only water stores within the urban area are considered, or 22 million, for the 100 km buffer zone model.
Remarkably, these aggregate figures differ very little among the various demographic and climate scenarios. The particularities of the challenge do however vary at the regional level. Perennial water shortage will generally be limited to cities in the Middle East and North Africa. Seasonal water shortages, on the other hand, will be geographically widespread, although rapidly urbanizing India and China will be especially hard hit.
The study acknowledges the temptation to view water shortage “as an engineering challenge.” Still, the lead author, Rob McDonald of The Nature Conservancy, cautions against exclusive reliance on grey infrastructure solutions (e.g. canals and dams) in an article for Nature Conservancy, saying:Some new infrastructure will be needed, of course – that’s the classic way cities have solved water shortages. But especially in parts of the world where there’s lots of cities, just going out farther or digging deeper to get water can’t be the only solution.
Instead, McDonald and co-authors Pamela Green, Deborah Balk, Balazs M. Fekete, Carmen Revenga, Megan Todd, and Mark Montgomery, emphasize the need for cities to encourage more efficient water use by their industrial and residential sectors, as well as the potential to engage the water-intensive agriculture sector in surrounding rural areas.
“Bottom line,” McDonald said in an interview with Robert Lalasz of The Nature Conservancy’s Cool Green Science blog, “don’t think of those high numbers as a forecast of doom. They are a call to action.”
Emanuel Feld is a student at Yale University studying economics and the environment.
Sources: Cool Green Science, PNAS, The Nature Conservancy.
Photo Credit: Adapted from “Chennai prayed too hard…. Part I,” courtesy of flickr user Pandiyan.Topics: Africa, climate change, development, environment, Middle East, population, urbanization, water
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