Water systems

Evaporation requires energy to break bonds between water molecules. This energy is absorbed from the surroundings, so the surroundings lose energy and cool down.

When water vapour condenses (gas to liquid), molecular bonds form and energy is released to the surroundings. The surroundings gain energy and warm up.

Matter: closed (same water recycled). Energy: open (solar energy enters, heat leaves).

The continuous movement of water between atmosphere, land, and oceans through evaporation, condensation, precipitation, infiltration and runoff.

Evapotranspiration is the combined total water loss from an area through both evaporation and transpiration.

A change of state of water, such as liquid to gas (evaporation) or gas to liquid (condensation).

Evaporation is liquid water changing to water vapour from non-living surfaces such as oceans, lakes, rivers or wet soil, absorbing latent heat.

Transpiration is the loss of water vapour from living plants through stomata in leaves, absorbing latent heat.

Examples include sweating cooling the body, feeling cold after swimming as water evaporates from skin, wet clothes making you feel colder, or a wet cloth cooling a fever.

Examples include storms/hurricanes intensifying as condensation releases latent heat, a warm bathroom after a hot shower as steam condenses, or steam burns being severe when steam condenses on skin.

Oceans, ice/glaciers, and groundwater (also rivers/lakes, atmosphere, living things).

Latent heat is the “hidden” energy absorbed or released during a phase change without changing temperature.

Energy absorbed or released during a phase change without a change in temperature.

Higher temperature, lower humidity, and stronger wind increase evapotranspiration (also greater vegetation cover and higher water availability).

Evaporation, precipitation, and runoff (also transpiration, condensation, infiltration, percolation).

Low humidity increases evapotranspiration because dry air can accept more water vapour, maintaining a strong diffusion gradient from surfaces and leaves.

(1) Condensation releases energy when molecular bonds form. (2) This energy is transferred to the surroundings. (3) The surroundings gain energy so temperature increases (warming).

Evaporation occurs from non-living surfaces, while transpiration occurs from living plants (via stomata).

(1) Evaporation requires energy to break molecular bonds. (2) This energy is absorbed from the surroundings. (3) The surroundings lose energy so temperature decreases (cooling).

Absorbed. Energy is required to break bonds as liquid water becomes water vapour.

Evaporation = from non-living surfaces. Transpiration = from plants (stomata). Evapotranspiration = both combined total water loss.

Both absorb latent heat from the surroundings during the liquid to gas phase change, producing a cooling effect.

Solar energy drives evaporation. Latent heat is absorbed during evaporation (cooling). Latent heat is released during condensation (warming). This transfers and redistributes heat within the atmosphere.

Wind removes moist air from the surface/leaf boundary layer and replaces it with drier air, increasing evaporation and transpiration rates.

Energy is absorbed at Earth’s surface during evaporation (often in warm regions) and released higher in the atmosphere during condensation, transferring heat and helping move energy around the planet.

Trees transpire large amounts of water vapour. This transpiration absorbs latent heat from the surroundings, lowering local air temperature.

Released. Energy is transferred to the surroundings as bonds form when vapour becomes liquid.

Matter is closed (no net water enters or leaves Earth). Energy is open (solar energy enters and heat energy leaves).

Because energy is used to break or form molecular bonds rather than increasing or decreasing kinetic energy, so temperature does not change.

A forest, because it has much more vegetation and leaf area (more stomata), so transpiration is far greater than in a desert.

Evaporation is the loss of water vapour from non-living surfaces such as oceans and lakes, whereas transpiration is the loss of water vapour from plants through stomata; both are driven by solar energy and absorb latent heat.

Deforestation reduces transpiration and evaporation from vegetation. With less latent heat absorption, less energy is taken from the surroundings, so local cooling decreases and temperatures rise.

Solar energy, which powers evaporation and drives energy transfers through phase changes.

Evaporation absorbs latent heat from the surroundings (cooling) whereas condensation releases latent heat to the surroundings (warming).

Evaporation absorbs latent heat; condensation releases latent heat.

About 97% is in oceans (saltwater) and about 3% is freshwater.

Because water absorbs, stores, and redistributes heat, reducing temperature extremes and helping stabilise climate.

An aquifer is an underground rock layer that stores water in pores and cracks.

Water can absorb a lot of heat energy with only a small temperature rise, so oceans act as heat sinks that buffer daily and seasonal temperature changes.

Evaporation absorbs latent heat (cooling) and condensation releases latent heat (warming), moving energy around the atmosphere.

Residence time is how long water remains in a store before moving to another part of the system.

Ocean currents redistribute heat from the tropics to higher latitudes; for example, warm currents can raise temperatures in nearby coastal regions.

Infiltration is water soaking into the soil surface. Percolation is water moving downward through soil/rock to groundwater or aquifers.

Ice and snow have high albedo so they reflect more solar radiation (cooling). When ice melts, darker water absorbs more radiation (warming).

If extraction exceeds recharge, aquifers can take centuries to refill, so water can run out within human lifetimes.

Catchment (drainage basin) is the AREA where water drains to one river. Watershed is the BOUNDARY line between basins.

A drainage basin is an area of land where all precipitation drains into a single river system, bounded by a watershed.

Precipitation is the main water input and solar energy drives processes like evapotranspiration.

A watershed is the boundary line (usually high ground like hills/ridges) that separates two drainage basins.

Examples include the source, tributaries, confluence, main channel, floodplain, and the mouth.

River discharge to the sea/lake and evapotranspiration are key outputs (also abstraction by humans).

A confluence is the point where two rivers or streams meet.

At the local scale a drainage basin is an open system: water enters as precipitation and leaves via evapotranspiration and runoff/discharge.

Water, sediments, and pollutants move through tributaries into the main river, so land use upstream can change flooding, water quality, and ecosystems downstream.

Because activities anywhere in the basin can change flow, sediment, and pollution, affecting ecosystems and people downstream.

High specific heat capacity, latent heat transfer (evaporation/condensation), ocean currents, water vapour greenhouse effect, and albedo effects of ice/snow.

High specific heat capacity: water absorbs lots of heat with little temperature change, so oceans buffer climate.

Evaporation absorbs heat (cooling). Condensation releases heat (warming).

Warming increases evaporation, raising atmospheric water vapour, which strengthens the greenhouse effect and causes further warming.

They move heat from the tropics toward the poles and return cooler water toward lower latitudes, redistributing energy.

Melting reduces surface albedo, exposing darker water/land that absorbs more solar radiation, increasing warming (ice–albedo feedback).

It is a greenhouse gas that traps heat, and it can increase as temperatures rise, strengthening warming feedbacks.

Oceans absorb CO2 from the atmosphere, reducing atmospheric warming, but increased CO2 dissolving can contribute to ocean acidification.

Ice and snow reflect solar radiation due to high albedo, producing a cooling effect.

Give several distinct mechanisms as separate points (one per sentence), such as specific heat capacity, latent heat transfer, currents, greenhouse effect, and albedo.

Water has an uneven charge distribution: oxygen is slightly negative and the hydrogen atoms are slightly positive, creating a dipole.

A weak attraction between the slightly positive hydrogen of one water molecule and the slightly negative oxygen of another water molecule.

Cohesion is attraction between water molecules; adhesion is attraction between water molecules and other surfaces (like soil or plant tissue).

Because its polarity allows it to surround and separate ions and other polar molecules, so they dissolve and can be transported.

Surface tension (from cohesion) supports small organisms at the surface and helps water move through plants via capillary action.

The energy required to raise the temperature of 1 kg of a substance by 1°C.

Water has a high specific heat capacity, so oceans heat up and cool down slowly, reducing temperature extremes near coasts.

Energy absorbed or released during a phase change (melting/evaporation/condensation) without a temperature change.

Evaporation requires energy (latent heat) which is taken from the surroundings, reducing local temperature.

Warming increases evaporation, adding more water vapour (a greenhouse gas) which increases warming further.

Water is less dense as a solid than as a liquid, so ice floats on liquid water.

Floating ice forms an insulating layer so water below stays liquid, allowing aquatic organisms to survive.

The upper layer of water where light penetrates enough for photosynthesis to occur.

Turbidity reduces light penetration, shrinking the photic zone and lowering photosynthesis and primary productivity.

Clear water allows deeper light penetration, supporting more photosynthetic organisms and often higher biodiversity in the photic zone.

Hydrogen bonding between polar water molecules causes unusual thermal, density, and solvent properties.

High specific heat capacity and high latent heat (especially during evaporation and condensation).

It makes water a solvent for ions and polar molecules, enabling nutrient transport and chemical reactions in organisms.

Because it prevents lakes from freezing solid, keeping liquid water and habitat available below the ice.

Hydrogen bonding makes water a stable climate buffer and a life-supporting solvent, shaping ecosystem productivity and survival.