Water systems

River discharge exceeding channel capacity so that water spills over the banks and covers the floodplain for days.

Also: riverine flood, overbank flood

A fast, violent rise of water in a small catchment or dry channel within hours of intense rain.

Water ponding and running over land where intense rain exceeds the capacity of the ground and the drains, away from any river.

Also: urban flood, ponding, drainage flood

Rising groundwater emerging at the surface in low ground, flooding basements and fields for weeks.

High river flow when a snowpack melts quickly in spring or under warm rain.

River water backing up behind an ice blockage and flooding adjacent land, sometimes with ice and debris.

Flooding downstream when a reservoir must spill or release water fast to protect its dam or to empty a surcharge.

A flood wave released when a landslide, moraine or ice dam that blocked a valley fails.

Also: landslide dam flood, moraine dam flood

A lake or inland sea standing above its normal shore for months, flooding shorelines and low-lying land.

A prolonged shortfall of rain against the local normal, the starting point of every other kind of drought.

Also: rainfall deficit, dry spell

Soil moisture too low for crops and pasture during the growing season, cutting yields and herd condition.

Also: soil moisture drought

Streamflow, lake and reservoir levels falling below normal, restricting supply, hydropower and river navigation.

Also: low river flow, reservoir drawdown

Aquifers drawn down faster than they refill, lowering wells and driving land subsidence and saltwater intrusion.

Also: aquifer decline

A rapid dry-down of soil caused by heat and little rain over a few weeks, hitting crops without a long drought warning.

Demand exceeding the water a system can deliver, so that rationing or cuts follow for homes, farms and industry.

Also: water scarcity, water rationing

A drought lasting decades over a large region, often deepened by warming, that empties reservoirs and aquifers and forces lasting changes in farming and settlement.

Also: multi-decadal drought, aridification

Shrinking or drying of a lake or inland sea from upstream diversion and drought, exposing toxic dust beds, collapsing fisheries and changing local climate.

Also: shrinking lake, terminal lake drying

Falling dry-season river flow once shrinking glaciers have passed their peak meltwater yield, removing a buffer for irrigation, hydropower and towns downstream.

Also: peak water, meltwater decline

Sea level pushed above the tide by storm wind and low pressure, flooding the coast.

The combined water level of storm surge on top of the astronomical tide, which is the level that actually reaches the shore.

Seawater overtopping or breaching the shoreline and flooding land, from surge, waves, high tides or a raised sea level.

Also: sea flood, overtopping

Flooding in tidal river mouths where river flow, tide and surge meet and block one another.

Also: tidal river flood

Repeated shallow flooding of low coast at the highest tides, with no storm needed.

Also: king tide, nuisance flooding, sunny-day flooding

A train of long sea waves from a sudden displacement of the sea floor or water column, flooding coasts even far from the source.

Also: seismic sea wave

A standing-wave oscillation of a lake, bay or harbour, after wind, pressure or an earthquake, that sloshes water onto shores.

An unexpectedly large ocean wave, far taller than its neighbours, that can sink or damage ships and platforms.

Also: freak wave

Large breaking waves that sweep people and boats off beaches, rocks and breakwaters.

Also: high surf, heavy swell

A narrow channel of water flowing away from the shore that pulls swimmers out beyond the breaking waves.

A long-term rise of mean sea level that raises the baseline for floods, erosion and saltwater intrusion.

Seawater moving into coastal aquifers and estuaries, making water too salty to drink or irrigate.

Also: seawater intrusion

Tsunami-like waves raised by a fast-moving pressure jump or squall line over shallow water, flooding harbours and beaches with little warning.

Also: meteorological tsunami

A spell of unusually warm sea water that stresses reefs, fish and kelp and fuels storms and rain.

A slow drop in sea-water pH as the ocean absorbs carbon dioxide, weakening organisms that build shells and skeletons.

Low-oxygen zones in sea water that suffocate fish and bottom life, often after algal blooms or from warming.

Also: dead zone, low-oxygen water

Strengthening of the density layering of the upper ocean as surface water warms and freshens, cutting nutrient and oxygen exchange and lowering productivity and fisheries.

Also: ocean layering, reduced ocean mixing

A spell of unusually cold seawater, from upwelling or cold-air outbreaks, that kills fish, turtles and corals and disrupts aquaculture.

Also: cold-water event, upwelling cold shock

A period of unusually warm lake or river water that lowers oxygen, kills fish, fuels toxic blooms and forces power plants to cut cooling.

Also: lake heatwave, river warming, thermal stress in rivers

Excess nutrients in water driving algal growth, oxygen loss and fish kills.

Also: nutrient enrichment

A surge of algae or cyanobacteria that releases toxins or strips oxygen, poisoning people, animals and fisheries.

Also: red tide, cyanobacterial bloom

Rising salt and ion levels in rivers, lakes and groundwater from road salt, mining, irrigation return and drought, harming aquatic life and corroding supply systems.

Also: river salinisation, road salt pollution, salinisation syndrome

Massive drifts of floating seaweed that pile on beaches and rot, releasing hydrogen sulphide, choking coastal waters and harming fisheries and tourism.

Also: seaweed inundation, sargassum strandings