Annemarie Schneider and other researchers from Boston University used NASA's Landsat and other satellites to analyze the growth of 30 mid-sized world cities between 1990 and 2000. According to this NASA/Goddard Space Flight Center news release, the results are spectacular.
For example, below are images from Landsat showing how Chengdu, in China, grew between 1990 and 2000.
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| Chengdu in 1990 |
Chengdu in 2000 |
Difference 1990 - 2000 |
Vegetation appears green, water looks blue, and built up land is depicted as purple. The map of urban land in 1990 is shown in yellow in the last panel, while new urban growth from 1990-2000 is shown in orange (Credit: Annemarie Schneider/NASA Landsat).
You can see other examples, such as Sacramento or Calgary, by reading this Goddard Space Flight Center feature story.
The study showed that some of these cities grew by as much as 25 percent during these ten years.
"Cities such as Johannesburg and Shanghai have grown extensively, and we need maps that reflect this," Schneider said. "These maps will not only be useful to scientists studying energy transfer, hydrology and climate interactions, but to social scientists trying to understand the land impacts of population and economic activity at a global scale."
To obtain a complete assessment of global urban areas, Schneider combined data from NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Terra satellite, with the Defense Meteorological Satellite Program's (DMSP) nighttime lights imagery and population density data from 2001.
Each data source has its advantages and disadvantages. For example, the MODIS imagery provides coarse 1 kilometer (0.6 miles) resolution data of the Earth, but has trouble distinguishing between urban areas and barren landscapes. Meanwhile, the DMSP nighttime lights data capture lit areas globally, but distributions of light do not represent built environments or patterns of settlement. Schneider compensated for inadequacies in each data source by fusing information from all three.
The researchers found three common spatial patterns among these mid-sized cities.
First, land developments have formed in clusters outside the city. While fairly common in the U.S., Schneider noticed this trend in large cities of China and India as well. Second, there are a number of cities where growth has occurred along roads leading out of the city. This trend poses challenges both to city managers and governments who must provide water, sewage, adequate housing, schools and health care services to dispersed people, and to the citizens, who face increasingly difficult commutes. Finally, Schneider found scattered, patchy development around cities, with less structure than the first two trends. This is the first time actual data have been used to confirm theories made by urban researchers during the last century.
The study was presented this week at the American Geophysical Union Fall Meeting in San Francisco (AGU 2003).
Here is a link to the abstract of the study, "Urban Growth as a Component of Global Change."
And for even more information, you can visit the Urbanization as a Component of Global Change website.
Source: NASA/Goddard Space Flight Center, December 12, 2003
12:58:56 PM
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