Storms and Rainfall

• Extended storms can cause the level of rivers to rise, resulting in mass flooding. For instance, South America witnessed flooding caused by heavy rains in September, 2008. The rains persisted for more than one month, and flooding resulted in more than 80 deaths across the continent.
  
  

Snowmelt

• During summers, the snow starts melting in the mountains. Excessive flow of water down to the rivers again results in flood.
  
  

Global Warming

• Global warming is causing the temperatures to rise. The excessive heating is not only causing snowmelt in the mountainous regions, but is also melting the massive snow belts in the Arctic and Antarctica regions. This is causing the sea level to rise, and the phenomenon is expected to cause massive floods in the future.
  
  

Low-lying Areas

• Naturally, an area that lies below the sea level is more prone to floods. The flow of rivers in such areas tends to slow down, causing an increase in the volume of water, ultimately resulting in a rise in water level and flooding.
  
  

Deforestation

• The process of clear-cutting trees causes the land to erode. The eroded rock and soil sediment fall down and rest on the beds of rivers and seas, causing an increase in the water level. In 1998, Yangtze, a Chinese region which had lost more than 85 percent of its forest over the past few decades, witnessed a destructive flood.
  
  

Dam Breakages

• Dams can be natural or manmade, but are created to store large quantities of water, thus regulating the flow of a body of water. When a dam breaks, it results in massive flow of water that mostly pours down to the dry lands.