Are there any smart solutions to mitigate this looming crisis?
In 1900, most people lived in the countryside, with a little over 10 per cent of the world’s population living in cities. (see graph from New Scientist: City Living - By 2007 most people will be urbanites. )
Scientists are predicting that by next year, for the first time in human history, more people on earth will be living in urban settings -in cities than in rural areas, and this will only increase.
"By 2025, according to one United Nations estimate, 60 to 70 percent of all people will live in cities. Many of the fastest-growing areas for city growth are in arid areas."
The current issue of New Scientist explores this growth phenomenon, proposing that Ecocities are the answer to solving future migration and urbanization problems.
"The migration from rural idyll to urban living can now be seen in the meteoric growth of megacities across the globe – there are now 20 such cities with populations over 10 million.
And the environmental impact they have on the planet could be catastrophic. But far from being parasites on the earth, cities could hold the key to sustainable living for the world’s booming population. All you need to do is build them right. Designers are already planning eco-cities - where you would recycle everything, cut car use, build energy efficient buildings, integrate your work place with living areas, and embrace urban farming"
In the past, planners have designed cities around cars rather than people.
The New Scientist cover page (see above) is interesting to explore. It illustrates the contrast in thinking from old to new. It shows neatly manicured organic gardens and urban farming replacing concrete roadways and cars. Rooftop gardens and trellises offer wintertime insulation and reflect heat in the summer as well as a local supply of fruits and vegetables, not to mentio noise reduction and fresh air. A sleek monorail whisks people from station to station. Glass enclosed tube-shaped walkways connect one energy efficient building to another. Hanging gardens and water fountains cool the air. Wind turbines and solar cells generate up to 85 per cent of the electricity used in buildings, and rooftop rainwater collectors supply 70 per cent of its water needs.
Later this year work is due to begin on such an ecocity project, an ecological island on the doorstep of Shanghai-called Dongtan.
"The plan is to develop a new way of living that could demonstrate to the world that rich cities don’t have to ruin the environment but could form a blueprint for future green cities."
Thanks to one of our blog readers, Meelena Oleksiuk from MIT, who is coincidently writing a term paper called Environmental Sustainability and the City: Planning Opportunities, which she was good enough to pass along.
In her term paper, Meelena offers a definition of Smart Growth:
"The following are the principles of Smart Growth, as outlined by The Smart Growth Network: mixed land uses; compact building design; a range of housing opportunities and choices; walkable neighborhoods; distinctive, attractive communities with a strong sense of place; open space; farmland; development directed towards existing communities; a variety of transportation choices; predictable, fair and cost effective development decisions; and community and stakeholder collaboration. The main focus of smart growth is on the minimizing of the human spatial and environmental footprint through the infill of already urban but neglected areas with simultaneous protection of unurbanized land."
Source: Lantsberg, Alex. Sustainable Urban Energy Planning: A Roadmap for Research and Funding. California Energy Comission, 2005.
Panacea or Persistent Problem?
But some scientists are not convinced that the effects of growing urbanization will be benign.
Human activities in arid urban environments can affect rainfall and the water cycle
A study by a climatologist in the department of geography at the University of Georgia has shown, using a unique 108-year-old data record and NASA's Tropical Rainfall Measuring Mission satellite, that arid cities such as Riyadh in Saudi Arabia and Phoenix have an effect on rainfall patterns around them.
As important, it appears that human activities such as land use, aerosols and irrigation in these arid urban environments affect the entire water cycle as well.
In the past half-century, cities have begun to expand in some of the Earth's most arid areas. While scientists have known for some time that the so-called "heat-island" effect of large cities such as Atlanta and Houston can affect their weather, they knew less about this effect and other processes in arid cities, such as Phoenix, which have experienced explosive population growth.
"Many of the fastest-growing urban areas are in arid regimes," said Marshall Shepherd, author of the report just published in the online edition of the Journal of Arid Environments. "Because their total rainfall is low, these areas have been largely ignored in studies on how human activities affect the water cycle. But these cities are particularly sensitive to such changes, since the water supply is so critical."
Cities in arid areas are excellent models for understanding human-induced changes in the water cycle. In most cases, the cities have shown great growth only in the last 30-50 years because of new methods of irrigation and ways to obtain water for daily use. In the case of Phoenix, Shepherd had access to a unique 108-year-old data record that covered pre-and post-urban times and for the first time confirmed that a statistically significant change in rainfall took place in certain areas of Phoenix from the late 1890s to the present.
The stakes in understanding how weather affects the water-cycle in all cities are enormous.
One of the most interesting findings in the new study was a 12-14 percent increase (which scientists call an anomaly) in rainfall in the northeast suburbs of Phoenix from the pre-urban (1895-1949) to post-urban (1950-2003) periods. A previous study first noted the possible anomaly but focused only on the post-urban period, so it was not clear whether the change was tied to post-1950 urbanization around Phoenix. It is hypothesized that this anomaly is related to urban-topographic interactions and possibly irrigation moisture. Indeed, the role of irrigation in changing the weather of cities in arid areas is one of the more intriguing findings, and one that will bear more study.
"We think that these human activities can actually alter the natural system and interact with monsoon flow and mountain convection," said Shepherd. The weather in Phoenix, in fact, is affected by both.
Riyadh has also shown significant grown in the past few decades, and its weather also has been affected by the heat-island affect. (The large surface of pavement and buildings actually increases the heat of a city area, and when that heat rises, it can change weather patterns in and near cities.) Precipitation patterns have changed in Riyadh as well, though the causes are less clear than in Phoenix. Ground data confirm a recent significant increase in rainfall around Riyadh.
Through use of rainfall records and information from the Landsat, Aster and TRMM satellites, Shepherd was able to demonstrate unusual patterns that clearly show how human activities are affecting the weather in arid regions. This study also illustrates how satellite data can be used to observe the changing landscape and climate in regions like the Middle East, where traditional measurements are sparse or inaccessible.
"The results showed us just how sensitive the water cycle can be to human-induced changes," said Shepherd, "even under arid or drought conditions. These findings have real implications for water resource management, agricultural efficiency and urban planning."
Indeed, weather and climate models for these areas must increasingly deal with patterns of urban land use, aerosols and irrigation if they are to help planners understand and predict these large-scale processes.
"It's fair to say we don't yet understand how all these variables work together to change the water cycle in these arid regions," said Shepherd, "but these cities live and die by their water supplies, and we must begin to study these anomalies more and find out how they work."
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