Water-related

Flooding is (1) an overflowing by water of the normal confines of a watercourse or other body of water; (2) an accumulation of drainage water over areas which are not normally submerged; (3) a controlled spreading of water for irrigation (WMO and UNESCO, 2012). 

Coastal flooding occurs from multiple sources, including storm surges, waves and swell, seiches, riverine and flash floods near the coast, tides, sea-level rise and tsunamis. It is most frequently the result of storm surges and high winds coinciding with high tides. The surge itself is the result of the raising of sea levels due to low atmospheric pressure. In particular configurations, such as major estuaries or confined sea areas, the piling up of water is amplified by a combination of the shallowing of the seabed and retarding of return flow (WMO, 2011; WMO, 2022).

Estuarine flooding is flooding over and near coastal areas caused by storm surges and high winds coincident with high tides, thereby obstructing the seaward river flow. Estuarine flooding can be caused by tsunamis in specific cases (WMO, 2011).

A flash flood is a flood of short duration with a relatively high peak discharge  (WMO, 2021). 

Overflowing by water of the normal confines of a watercourse or other body of water (WMO, 2012). 

A groundwater flood is the emergence of groundwater at the ground surface away from perennial river channels or the rising of groundwater into man-made ground, under conditions where the ‘normal’ ranges of groundwater level and groundwater flow are exceeded (BGS, 2010). 

An ice-jam flood including debris is defined as an accumulation of shuga including ice cakes, below ice cover. It is broken ice in a river which causes a narrowing of the river channel, a rise in water level and local floods (WMO, 2012).

Shuga is defined as the accumulation of spongy white ice lumps, a few centimetres across, formed from grease ice or slush, and sometimes from anchor ice rising to the surface (WMO, 2012).

A ponding flood is a flood that results from rainwater ponding at or near the point where it falls because it is falling faster than the drainage system (natural or man-made) can carry it away (WMO, 2006). 

A snowmelt flood is a significant flood rise in a river caused by the melting of snowpack accumulated during the winter (WMO, 2012). 

Surface water flooding is that part of the rain which remains on the ground surface during rain and either runs off or infiltrates after the rain ends, not including depression storage (WMO, 2012).