Push and pull factors
Migration involves the permanent relocation of populations, generally due to what are called push and pull factors. Push factors are forceful, driving people from their homes, while pull factors attract people away from their homes. Often these factors are environmental. Environmental pull factors are physical attractors: warm or temperate climates, coastal areas, or mountain views, while environmental push factors usually involve adverse physical conditions.
One such push factor would be floods. A modern-day example of this would be the flooding of New Orleans in 2005 by Hurricane Katrina. In the days following Katrina, about 400,000 people were displaced. It has been estimated that, ultimately, 1.5 million people have been driven from the Gulf Coast by hurricanes Katrina and Rita to find new homes throughout the southeast region and beyond. In a more global aspect, as theories of global climate change gain credence, it is conjectured that more people, especially those living in low-lying, densely populated regions, will become "environmental refugees" due to sea level rise and extreme weather events such as 2012's Hurricane Sandy, factors which will increase the severity of flooding and soil salination.
Drought is another environmental push factor driving migration and settlement patterns. A Pre-Columbian example would be the Hopi Indians, sophisticated dry-farmers of the desert Southwest, whose population centers were abandoned during a drought lasting almost a quarter of a century in the late 1200s CE. A more recent example would be the eight-year Dust Bowl drought of the 1930s. The Dust Bowl covered an area of eight states, an ecological disaster brought on by poor farming practices. By 1940, about 2.5 million people had moved out of the Plains states. Many environmental push factors bring negative economic consequences as well, adding one more push factor that causes people to move to a different environment.
Learning Activity
The present-day New Delhi, India, is actually the eighth incarnation of the city of Delhi. In different historical eras, war, earthquakes, famine, or other events have periodically ended the life of the city. When this has happened, another Delhi has risen nearby, always calling itself "New" Delhi. What factors have led to this city's site being maintained for such a long period of time, despite disruptive events? Why have other historic cities been abandoned after natural disasters or discord? Click on the following sites to gather information for your response to this question.
http://en.wikipedia.org/wiki/New_Delhi#Geography
http://www.atlasobscura.com/articles/five-towns-abandoned-after-disasters
