Floods are one of the most powerful – and deadly – forces on earth, claiming more lives in the United States than any other weather phenomena. It is vital to understand the scientific principles behind flooding so as to aid in their prevention and protect those impacted by this common occurrence.
A basic understanding of water can illuminate the basis for flooding. Despite the fact that it appears that humans use up water, the amount on the planet actually remains about the same, and has so for millions of years. A small amount is lost in the upper atmosphere but this is offset by the same amount that is created by volcanic activity in the inner Earth.
The distribution of water is anything but constant, however. How it is spread throughout the earth changes. Also, it comes in many different forms such as liquid (oceans, rivers, lakes), solid (ice of the poles) and gas (water vapor in the air, which cannot be seen). Wind currents help to change the form of water and create a cycle.
The cycle of water occurs every day on earth. The heat from the sun causes the liquid water of the ocean to transform into a gaseous state. It ascends through the atmosphere, carried by wind currents. As it cools, it condenses, and clouds are formed from little droplets of water or ice. When enough condenses so that it is too heavy to sustain itself, precipitation occurs and the water once again returns to the earth. It flows into rivers and streams, which subsequently flow into the ocean to begin the cycle again.
When looked at over time the wind currents are fairly consistent, and thus the cycle of water is as well. Specific rivers, lakes, ponds, streams and other bodies that manage the water are created. They are created to handle the “normal and predictable” amount of precipitation. The problem occurs because on a daily basis the weather is not so predictable. Thus the danger for flooding arises.
The daily weather in an area can range greatly. Temperature changes, seasonal affects and other weather factors can all change the weather to create more precipitation than the area typically handles. Floods occur when the precipitation in one area is of a greater amount than this area normally receives. The natural waterways cannot handle this excess water. The water overflows the banks and runs into the land, accumulating in places populated by humans and animals.
Flooding often occurs when there is a long or sustained amount of thunderstorms in an area. As the rain continues to pour, the waterways cannot handle the excess water and it overflows. Humans build artificial barriers such as dams to protect against flooding in susceptible areas, but in many cases even these can be overwrought by nature.
An event such as a hurricane can also cause flooding. In these cases, rain comes extremely hard for a sustained period of time. Because of the intensity, the water does not get a chance to evaporate or dry out before it overflows.
Another factor in flooding is the absorbency of the nearby land. Soil can soak up water to a great extent just as a sponge would. When the land has been relatively dry, the water from the flooding may be absorbed by the land and have less of an impact. If that becomes saturated or if there is no soil to absorb it then the impact may be greater. If it is in a populated area, it will also depend on the drainage and other systems put in place to avoid flooding.
Floods are a common and unfortunate occurrence on Mother Earth. As understanding of the patterns and dangers occur, life -saving measures will hopefully be undertaken to reduce floods and their impact.
Resources:
http://www.livescience.com/6592-science-flash-floods.html
http://www.brainpop.com/science/earthsystem/floods/preview.weml
http://www.fema.gov/kids/floods.htm
http://science.howstuffworks.com/nature/natural-disasters/flood.htm
