Visualizing Beijing's urban sprawl

© NASA / JPL-Caltech

If you ever wondered how a three-dimensional computer model simulation of Beijing's frantic process of urbanization would look like, well, here it is:

Using data from NASA's QuikScat satellite, scientists of Stanford University, NASA's Jet Propulsion Laboratory at the California Institute of Technology and the University of Southampton (UK) were able to assess the city's urban expansion between the years 2000 and 2009 based on detected changes in physical infrastructure.

According to the press release from June 25:

'Gray and black indicate buildings, with the tallest and largest buildings in the city's commercial core appearing lighter gray. Other colors show changes in areas not yet urbanized (for example, clearing land or cutting down trees), with the rate of change indicated by color. Blue-green indicates the least change, yellow-orange more change, and red the greatest change.'

The new study finds that the Chinese capital virtually quadrupled in size during this time alone, leaving it to further analysis to determine how much the burgeoning mega-city has expanded since then.

Interestingly, the researchers also quantified how this phenomenal urban sprawl has modified Beijing's wind and pollution patterns by using a computer model of climate and air quality created by one of the two team leaders.

Not surprisingly, even winter temperatures have risen by circa 3 to 4 degrees Celsius and wind speed has been reduced by approximately 1 to 3 meters per second. Higher temperatures and less air circulation are highly consequential, of course, leading to more ozone pollution on the ground, for example.

Even if Beijing's administrative city limits encompass an enormously large area, it doesn't mean this space reflects its 'actual footprint', as team leader Son Nghiem of NASA's Jet Propulsion Laboratory cautions.

Nghiem succinctly points out:

'There are so many definitions of urban extent, both legislative and administrative. To learn how physical change affects the environment, you cannot use an arbitrary political definition. The reality is what's happening on the ground.'

And that's exactly what the novel technique permits scientists to specify. For everyone who wants to delve deeper into the details of this fascinating study:

The full article, to be published in the next issue of the Journal of Geophysical Research: Atmosphere, is available online here (paywall).