The explosive growth of cities worldwide over the next two decades poses significant risks to people and the global environment, a new study has claimed.
Researchers from Yale, Arizona State, Texas A&M and Stanford universities have predicted that by 2030 urban areas will expand by 590,000 square miles to accommodate the needs of 1.47 billion more people living in urban areas.
"It is likely that these cities are going to be developed in places that are the most biologically diverse. They're going to be growing and expanding into forests, biological hotspots, savannas, coastlines -- sensitive and vulnerable places," lead researcher Prof Karen Seto of Yale University said.
Urban areas, they found, have been expanding more rapidly along coasts. "Of all the places for cities to grow, coasts are the most vulnerable. People and infrastructure are at risk to flooding, tsunamis, hurricanes and other environmental disasters," said Seto.
The study provides the first estimate of how fast urban areas are growing and how fast they may grow in the future.
"We know a lot about global patterns of urban population growth, but we know significantly less about how urban areas are changing. Changes in land cover associated with urbanisation drive many environmental changes, from habitat loss and agricultural land conversion to changes in local and regional climate," she said.
The researchers examined peer-reviewed studies that used satellite data to map urban growth and found that from 1970 to 2000 the world's urban footprint had grown by at least 22,400 square miles -- half the size of Ohio.
"We found that 48 of the most populated urban areas have been studied using satellite data, with findings in peer-reviewed journals. This means that we're not tracking the physical expansion of more than half of the world's largest cities," Seto said.
The study has been published in the latest edition of the 'PlosOne' journal.