Relatively sudden and widespread disturbance of the social system and life of a community or region may be a result of the action or interaction of mechanisms or processes set up by man.
The vulnerability of rural and urban populations to natural disasters is growing due to population increase and inadequately planned urbanization. The number and density of people living in cities within earthquake and tropical cyclone zones have risen dramatically in the past two decades. In many developing regions, population pressures and poverty are forcing farmers to cultivate marginal and vulnerable areas in flood plains or on hill slopes. Poor planning decisions have also led to siting potentially-hazardous facilities, such as nuclear power plants, chemical factories and major dams, in earthquake zones and densely-populated areas.
The last decade of the twentieth century witnessed fires on an unprecedented scale in the tropical forests of Brazil and Indonesia, coral bleaching that has left vast areas of reef in the Caribbean, Indian and Pacific oceans as ghosts of their former selves, the collapse of commercially viable fish stocks in the Atlantic, the ecological devastation of the Black Sea, Aral Sea and Lake Chad, and the continual loss of precious wetland and freshwater ecosystems around the world.