As our population grows we find our cities getting bigger. Sometimes they grow up, with huge skyscrapers and tall building. In other cases they grow out, with new developments around the city. In either case, the results can be destructive for the surroundings. The worst consequence of the overpopulation of cities is an increase in urban sprawl, which can have devastating impacts on the environment, such as nonpoint source pollution, fires and flooding.

Urban Sprawl is the unplanned, uncontrolled spreading of urban development into areas adjoining the edge of a city. A new housing development just outside of town, a strip mall or a sports complex are examples of urban sprawl. They all turn what was once some kind of natural wilderness into a “human friendly” environment, complete with buildings, roads, parking lots, and all the problems that comes with them.

The first major problem is nonpoint source pollution, or NPSP as it is sometimes referred to. Unlike pollution from industrial and sewage treatment plants, nonpoint source pollution comes from many diverse sources. It is caused by rainfall or snowmelt moving over and through the ground. As the runoff moves, it picks up and carries away natural and human-made pollutants that are only there because of human interference. The runoff finally deposits those pollutants into lakes, rivers, wetlands, coastal waters, and even our underground supplies of drinking water.

Sources of this type of pollution can be simple and widespread and most are a result of urban sprawl. In a parking lot, for example, a car may be leaking oil or some other chemical may have been spilled. Garbage and trash may also accumulate in this area, and when it rains all of these contaminants flow off of the parking lot and into the nearby forests or streams. Roads and parking lots can be very spread out and unlike a smokestack or sewage pipe there is no way of monitoring what pollution they are discharging. The overpopulation of cities is causing these giant paved areas that can contribute to nonpoint source pollution.

The next problem that can occur with the overpopulation of cities and urban sprawl is wildfires. Wildfires can be a natural and healthy part of an environment. They can get rid of old growth and allow new growth to form in forests, grasslands and even wetlands. Wildfires have always been an ordinary, helpful occurrence. Many types of plants can only reproduce after a fire has raised their temperature and cleared the ground of any foliage that can harm the plant.

The problem comes in when humans create unnatural environments in the ecosystems that used to be there. People do not want a natural wildfire to occur in a forest if they have built a house in that forest. If there were a wildfire, that house would probably be destroyed. The people who live in the forest therefore try to prevent forest fires. This can have devastating effects on the ecosystem.

First, the vegetation of the area can change dramatically when no natural wildfires occur. The plants that rely on fire to reproduce cannot do so. The plants that are controlled by fire are allowed to continue growing and suffocate out other species around them. Since fire was a natural force that was expected by the environment, eliminating it would mean upsetting the balance of the forest. It may seem counterintuitive that by stopping a forest from burning we are actually doing harm but in many cases this it true.

Second, although humans have made enormous gains in subjugating the environment, we do not fully have that ability yet. Therefore when there finally is a fire in one of these areas, it is huge. There is so much underbrush that hasn’t been cleared away by past fires that it will move and grow very fast and reach very high temperatures because of all the fuel that is readily available. Trees that can survive the relatively low temperature fires that used to occur cannot withstand the intensity of the fires that are possible in the context of urban sprawl. The ecosystem can survive the small fires but cannot survive the large ones that humans, and our desire to be away from everyone else, can cause.

Allowing a forest to grow unchecked by natural forces can cause devastating fires, but on the other end of the spectrum, however, humans often don’t let the forests grow which can cause flooding. Creating new developments with perfectly manicured grass and driveways and building malls and parking lots destroys more than just the land we develop. When we pave over a piece of ground and take out the plants that were there we are tampering with the course of water. Instead of being absorbed into the ground like it normally would, the rain water or snowmelt flows along the ground and onto ground that may be already saturated with water. If this happens over a great enough area and for a long enough time then the results can be quite serious.

When water runoff goes unchecked one of the first things that can happen is flooding. The water has a clear ride to the nearest river or steam, which can become overwhelmed with the increased volume of water and begin to overflow its banks. Rather than being absorbed into the ground and slowed down, or being used by the vegetation in the ground it can go right into a body of water.

Another common occurrence when runoff occurs is mudslides. Instead of flowing directly into a river or stream the rainfall or snowmelt is sometimes deposited on an undeveloped piece of land were it can be absorbed. But the ground can only hold so much moisture before it begins to turn into a stream itself. If the water from dozens of acres is be channeled onto one spot then that ground can sometimes just not withstand the intense saturation and the ground will begin to collapse and give way.

With our population getting bigger and our cities becoming larger, people must go somewhere. Often that leads to disastrous consequences. First is nonpoint source pollution, which is hard to track or contain. Next are wildfires, which were once a part of a healthy ecosystem, but can now cause huge amounts of damage. And finally, flooding which comes from the diversion of rainfall and snowmelt. All of these problems come from the expansion of the sphere of human influence, which is directly related to overpopulation.

www.answers.com/topic/urban-spraw

http://www.worldwildlife.org/forests/fires.cfm

http://www.srs.fs.usda.gov/pubs/20314