|Part two of a three part series.
Part 1: Bright Lights, Big City
Part 3: Urbanization’s Aftermath
When most animals in the wild multiply to the point where they require more food than is available in their habitat, they eat what they can and then starve in droves. From dinosaurs to present-day deer populations, this basic rule of nature has held fast for nearly every animal species with one notable exceptionus. Many anthropologists believe that 10,000 years ago, when the human population reached its natural limit of 10 million people (Imhoff et al., 2000), the agricultural revolution began so that the hunter-gatherers could ensure their survival. Ever since, we humans have been growing in number, precariously and diligently avoiding what seems to be a Malthusian fate by engineering new ways of reviving our soil, changing the flow of the Earths water, and even genetically altering our crops.
Now that the number of people on the planet has surpassed the six billion mark, it is more important than ever that we actively protect our natural resources. Yet, many researchers fear we may be doing the exact opposite. As our population continues to swell, our self-made urban and suburban habitats have begun to consume enormous tracts of once rural landscape. What is worse, some researchers believe, a majority of this landscape is prime farmland.
Tracking this phenomenon, however, has always been difficult. Urbanization moves relatively fast and its outlines are often hard to discern. Recently, a group of researchers at Goddard Space Flight Center, led by climatologist and remote sensing specialist Marc Imhoff, came across a solution. Using satellite images of city lights at night, they constructed a map of the urbanized areas of the United States and several other countries. They then integrated this map with a soil map that the United Nations prepared. These NASA researchers found that while the residents of these countries are not going to starve tomorrow, they may indeed be destroying their best soils and putting future generations at risk.
|The Aura of Urbanization|
Since researchers first suspected that this trend was taking place, the single biggest problem in tracking it has been in finding a way to measure the full extent of urbanization across very large regions, such as whole continents. Several years ago, Imhoff came across a solution. He discovered satellite images displaying the illumination cities and towns generate at night. The images were taken by the Defense Meteorological Satellite Programs Operational Linescan System (OLS). The satellite network was originally designed to aid in aircraft navigation by detecting the lunar illumination off of nighttime clouds. What the Air Force realized is that on evenings when there was a new moon, the satellite was sensitive enough to record the illumination from city lights. Over a period of several new moons, the data the satellite retrieved could be pieced together to produce a global image of city lights.
Using computer algorithms, Imhoff figured out a way to create maps of the approximate population density across an entire country or continent from the images (see Bright Lights, Big City). "We essentially scaled back on the brightness levels of the imaging data," says Imhoff. The first full map of population density he constructed was of the United States. With help from U.S. Census Bureau statistics, the Goddard team was able to classify all land area in the United States into three categoriesurban, peri-urban, and non-urban areas.
An urban region, Imhoff elaborates, is defined as an area with 1000 people or more per square mile. These are regions where humans have developed and completely transformed the natural ecosystem. Any scientist looking at a region classified as urban on the map can be fairly certain that there are parking lots, office buildings, some strip malls, and maybe a fast-food restaurant or two. Peri-urban areas, on the other hand, have only been lightly populated. They usually consist of farmland, light suburban development or small towns and are classified as having an average of 100 people per square mile. In most instances, this is the type of land development that occurs as cities expand. Finally, non-urban areas are regions such as central Montana and western Maine, where only ten people or less live per square mile.
Based upon satellite measurements of city lights, this image is a map of the urban population density of North America. Red yellow and green are urban areas, and blue is peri-urban. The city light data is laid over elevation data (black is sea level, light grey is over 10,000 feet). Most major cities are in level areas along an ocean bay, large lake, or navigable river. (Image courtesy Marc Imhoff, NASA GSFC, and Flashback Imaging Corporation, Ontario, Canada)
|Saving What Weve Got Before Its Gone|
What does all this mean for the U. S.? For now, Imhoff believes that
the United States still has plenty of good soil and that we are not
going to run out of food anytime soon if we work to curb our urban
sprawl. However, in other countries there is possibly more to worry
about in the near future. "We did a similar study in China,"
says Imhoff. "In China, theyre also having the same trends.
The best soils are being developed now with their increased economic
development. But they have fewer soils to rely on." Probably the
worst-case scenario is in Egypt. They have very little arable land and
it is all along the Nile Delta where everybody lives. As the population
in Egypt expands, people either have the choice of building on prime
farmland or of moving out onto very inhospitable areas of the Sahara.
In order for the world to save its farmlands for future use as the
population expands, Imhoff feels that city planners need to start
building and developing city infrastructure on rocky, non-level, and
arid soils. "I think that land use planning has to have some teeth.
We need to leave the land that is productive in agricultural use,"
he says. Until then the Goddard team will continue to monitor the U.S.
as well as other countries and alert people to this problem before we
get to the point where we have plenty of big lawns and convenience
stores, but very little food.
A photograph of Cairo, Egypt, taken from the space shuttle. Located at the southern end of the Nile Delta, Cairo is one of the worlds fastest growing cities. It is also located on what was once prime farmland. Grey urbanized areas are continually eating into the green cropland along the Nile RiverEgypts only arable land. (Photograph courtesy NASA Johnson Space Center Astronaut Photography)
World Resources Institute, 1996: World Resources 1996-97, Washington, DC.
Among the soil types shown, only fluvisols are suitable for farming. Fluvisols are soils deposited by flowing water, specifically the rich silt laid down by the Nile Rivers annual flooding. Other soils in Egypt are too dry, too salty, or too rocky for farming. (Image courtesy Marc Imhoff, NASA GSFC)