Causes of flood:-
There are several causes of flood like due to heavy rainfall, overflowing of the river, cloudburst, snowmelt due to global warming, landslide of the nearby mountain of the river , Catastrophic flood etc.
Now I am explaining few of these reasons.
Global warming is causing disastrously to put us on the verge of creative flood. Temperature rise on each ear raises the sea level due snowmelt of polar region and also that of mountains. These excess water raises the sea level that ultimately is affecting the rivers to flow over its banks. At this situation heavy rainfall is adding to turn the situation in rampant and is submerging the non-flood zone also.
Rapid flooding events more often occur on smaller rivers, rivers with steep valleys or rivers that flow for much of their length over impermeable terrain. Catastrophic flood occurs when a dam gets collapsed or may also be caused by earthquake inside the sea. Tsunami waves at 9.1 magnitude mainly had brought costal flood in Indonesia in 2004 (26 December) and caused death toll of more than 230,000 people; which is one of the most dangerous flood in the history. This Catastrophic flood also devastated the costal area of Bangladesh, Thailand, Maldives, Somalia, India and Srilanka.
In the year 2013 Utterakhand, Gujrat and West Bengal suffered a lot due flood. Particularly Flash Flood, landslide and cloudburst turned mandakini and alaknanda into torrential streams ; which devastated major costal area of the Mandakini and alaknanda river of Utterakhand in India.
Conlusion: Recent flood events have raised many questions that has to be taken into account to take necessary and precautionary measures so that human lives could be protected from various types of flood.
Utterakhand was natural Catastrophic flood which was forcasted well ahead of 16 April 2013, but our metereological department failed to forcasted it's intensity. So there should be more research and development regarding this.
We all people must do our best to stop soil erosion that are minimising the river's depth; which in turn causing rivers to flow over its bank. And we must be aware and responsible to check manmade causes of flood to work for the wefare of whole mankind.