Aerial view of illuminated cityscape, Las Vegas, Nevada, United States.

Las Vegas, Nevada, is among the many US cities that has exploded in area over the last few decades. Credit: Getty

Geography

Urban sprawl overspreads Earth at an unprecedented speed

Satellite imagery shows that although the global population is growing, urban areas are growing even faster.

Cities around the world have sprawled across a far greater area in the last three decades than scientists had thought.

Satellites can track urban sprawl from above, but the observations aren’t always detailed or taken consistently over a long period. Xia Li at East China Normal University in Shanghai, Zhenzhong Zeng at Princeton University in New Jersey and their colleagues used satellite images to map urban growth between 1985 and 2015. Each image captured 900 square metres of ground, a level of detail that allowed the scientists to study land-use change over time.

Urban areas expanded 80% over the measured period. Each year, an average of 9,687 square kilometres of land — an area bigger than New York City — converted from non-urban to urban uses. That’s four times greater than one previous estimate.

In China and India, urban growth occurred mostly within and around a handful of large cities. A much greater number of cities accounted for the bulk of US urban growth.

The rate of urban growth is substantially higher than the global rate of population growth, the authors found.