WASHINGTON šC While a city is not a living organism, it behaves very much like one. Its metabolic processes may be manifested in growth spurts, metamorphosis over time and even decay. Researchers using satellite imagery have tracked the vital signs of six major global cities, detecting a distinctive ¡°urban pulse¡± in each.

The researchers looked at Dubai, Lagos, Mexico City, Mumbai, Seattle and Shenzhen using a new way to document dynamic changes unfolding in each ?of these cities in near real-time.

Historically, experts have relied upon aggregated and infrequent data to document urbanization, such as a yearly census, annual ?economic figures ?or a map showing how a city¡¯s footprint has changed over a decade ¡ª essentially using specific outcomes as metrics. But ?the scientists behind the new study said such an approach provides an incomplete understanding of a city and can miss the nuances as a metropolis evolves.

¡°We got the inspiration from the human pulse, which tells us different information about our health than weight or height,¡± said study lead author Zhe ?Zhu, a professor of remote sensing and director of the Global Environmental Remote Sensing Laboratory at the University of Connecticut¡¯s Department of Natural Resources and the Environment.

¡°The urban ?pulse measures the high-frequency process of development, and therefore we can spot early warning signs of economic stress or stagnation before they become full-blown crises,¡± Zhu said. ¡°We compare traditional metrics to looking at a heart attack ¡ª the outcome ¡ª whereas the ¡¯urban pulse¡¯ is like monitoring the ?daily lifestyle and vital signs leading up to that heart ?attack ¡ª the process.¡±

The biggest takeaway from the study, published in the journal Proceedings of the National Academy of Sciences, is that urbanization is not smooth and steady, the researchers said.

¡°Urbanization is actually ¡¯spiky,¡¯ meaning that it ?happens in abrupt and?intense bursts,?¡¯cyclical,¡¯ moving ?through boom-and-rest phases that don¡¯t match annual seasons, or ¡¯asynchronous,¡¯ as different neighborhoods in the exact same city ?develop at completely different, uncoordinated times,¡± said study senior author Karen Seto, a Yale University professor of geography and urbanization science.

¡°This ?is important because, ?for decades, researchers have characterized cities through static maps,¡± Seto said.

The researchers used dense and high-frequency satellite imagery from?NASA¡¯s Landsat and the European Space Agency¡¯s Sentinel-2 satellites. They tracked physical changes in the cities such as new building construction, demolition, major infrastructure improvements and expansion into green spaces.

¡°We selected cities with a wide range of political-economic conditions including the state-led development of ?Shenzhen, the market-driven growth of Seattle, the informal expansion of Lagos and the megaprojects of Dubai,¡± Zhu said.

Shenzhen, formerly a small fishing village near Hong Kong that has become a megacity, exhibited the highest magnitude...