What do hydrological disasters include?

Hydrological disaster is a violent, sudden and destructive change either in quality of earth’s water or in distribution or movement of water on land below the surface or in atmosphere. Flood and limnic eruption are hydrological.
   A flood is an overflow of an expanse of water that submerges land. The EU Floods directive defines a flood as a temporary covering by water of land not normally covered by water. In the sense of "flowing water" , the word may also be applied to the inflow of the tide. Flooding may result from the volume of water within a body of water, such as a river or lake, which overflows or breaks levees, with the result that some of the water escapes its usual boundaries. While the size of a lake or other body of water will vary with seasonal changes in precipitation and snow melt, it is not a significant flood unless the water covers land used by man like a village, city or other inhabited area, roads, expanses of farmland, etc.
   A limnic eruption occurs when a gas, usually CO₂, suddenly erupts from deep lake water, posing the threat of suffocating wildlife, livestock and humans. Such an eruption may also cause tsunamis in the lake as the rising gas displaces water. Scientists believe landslides, volcanic activity, or explosions can trigger such an eruption. To date, only two limnic eruptions have been observed and recorded: In 1984, in Cameroon, a limnic eruption in Lake Monoun caused the deaths of 37 nearby residents. At nearby Lake Nyos in 1986 a much larger eruption killed between 1, 700 and 1,800 people by asphyxiation.