Floods represent encroachment of water over land that is usually dry. In the sense of “flowing water”, the word may also be applied to the inflow of the tide. Human induced changes to the environment often increase the intensity, and frequency of flooding; for example land use changes such as deforestation, and removal of wetlands, changes in waterway course or flood controls such as with levees, and larger environmental issues such as climate change, and sea level rise.
Flooding may occur as an overflow of water from water bodies, such as a river, lake, or ocean, in which the water overtops or breaks levees, resulting in some of that water escaping its usual boundaries,or it may occur due to an accumulation of rainwater on saturated ground in an areal flood. While the size of a lake or other body of water will vary with seasonal changes in precipitation and snow melt, these changes in size are unlikely to be considered significant unless they flood property or drown domestic animals.
Floods can also occur in rivers when the flow rate exceeds the capacity of the river channel, particularly at bends or meanders in the waterway. Floods often cause damage to homes, and businesses if these are located in the natural flood plains of rivers. While riverine flood damage can be eliminated by moving away from rivers, and other bodies of water, people have traditionally lived, and worked by rivers because the land is usually flat, and fertile, and because rivers provide easy travel, and access to commerce, and industry.
Flooding can lead to secondary consequences in addition to damage to property, such as long-term displacement of residents, and increased spread of waterborne diseases, and vector-borne diseases transmitted by mosquitos.
Large proportion of the Indian subcontinent is prone to seasonal floods. The hill areas often experience flash floods that are caused by sudden, and heavy localised rainfall in the catchment area of rivers and streams. The Himalayan state of Uttarakhand has witnessed severe floods in 2010, 2012, and 2013 of which 2013 flooding of Mandakini valley caused major devastation, and human losses around Kedarnath, Rambara, and Gaurikund.