What are the causes of a flash flood?

Flash floods occur due to both, manmade and natural causes. Given below are a few of the most common causes of flash flooding:

1. A few minutes or hours of excessive rainfall
2. Failure of a dam or levee
3. Sudden release of water held by an ice jam
4. Persistent thunderstorms over the same area for extended periods
5. Combined rainfall and snowmelt

Further Reading: 

• What are Floods?
• Indian Meteorological Department