Floods are the most common and widespread of all natural disasters. A flood occurs  when the water level rises in an area where there was normally little or no water before. Floods can occur dramatically and quickly or could happen slowly over a time.
Floods are natural phenomena common in many places around the world where there is either a river nearby or the local weather can dump large amounts of rain. Usually floods happens due to severe weather conditions such as extreme rainfall which may result in sudden increase of water level or due to overflow of rivers or streams or bursting of dam or river banks.

What Are Flash Floods? Flash floods are short-term events, occurring within few hours (2-8hrs) of the causative event (heavy rain, dam break, levee failure, rapid, snowmelt and ice jams) and often within 2 hours of the start of high intensity rainfall. A flash flood is characterized by a rapid stream rise with depths of water that can reach well above the banks of the creek. Flash flood damage and most fatalities tend to occur in areas immediately adjacent to a stream or arroyo. Additionally, heavy rain falling on steep terrain can weaken soil and cause mud slides, damaging homes, roads and property.

How Flash Floods Occurs: ?

Since many flash floods occur along small streams, you can determine your risk by knowing your proximity to streams. Flooding can be caused by rain that falls several miles upstream and then moves rapidly downstream. Highly populated areas have a high risk for flash floods. The construction of buildings, highways, driveways, and parking lots increases runoff by reducing the amount of rain that the ground can absorb. This runoff increases the flash flood potential. Sometimes, streams through cities and towns are routed underground into storm drains. During periods of heavy rainfall, storm drains may become overwhelmed and flood roads and buildings. Low spots, such as underpasses, underground parking garages and basements can become death traps. Embankments, known as levees, are built

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Is Global Warming led climate change is causing more floods?

As climate continue to change due to global warming, scientists believe that frequency and severity of  such weather patterns such as severe rainfall, more powerful hurricanes and violent floods may be linked to it. They are predicting that more extreme rainfall and greater flooding may occur this century.
According to their projections, it will be particularly striking at northern latitudes—across Canada, Alaska, northern Europe, and northern Asia, regions that already receive the most precipitation. But the equatorial tropics and Southeast Asia are also likely to have increased rainfall and flooding.

Can floods be predicted:

Several types of data can be collected to assist hydrologists in predicting when and where floods might occur. The first and most important is the amount of rainfall occurring on a real-time basis, and second is the rate of change in river stage on a real-time basis. The rate of change can help indicate the severity and immediacy of the threat.

Type Of Floods:

Estuarine floods
Estuarine floods are caused by surge in sea tides which in turn may be caused by storm winds.
 

Riverine floods
They are usually flooding of creek due to heavy monsoonal rain a runoff from sustained rainfall or rapid snowmelt exceeding the capacity of a river's channel. flash floods are examples of these floods

Coastal floods
Caused by severe sea storms, or as a result of another hazard (e.g. tsunami or hurricane).

Catastrophic floods
Can be caused by bursting of dam due to earthquake or volcanic eruption.