There are many causes for such condition to arise, and there are different types of flooding. A Flood is commonly called River Flood when there is high flow or overflow of water from a river or similar body of water. Flash Floods are quick-rising floods that usually occur as the result of heavy rains over a short period of time, few hours or less. Several factors contribute to flooding. The two key elements are rainfall intensity and duration.
Intensity is the rate of rainfall, and duration as in how long the rain continued.
Topography, soil conditions, and ground cover also play an important role. Floods occur within a few minutes or hours of excessive rainfall, a dam breakage, or a sudden release of water held by an ice jam. Flooding is not restricted to specific areas or to a specific country. Certain geographical locations may be more prone to annual flooding from a sudden rainfall. A drought can set in when an expected rainfall does not arrive or does not last for long.