- Define the hydrological cycle and describe how water is stored and moved.
- Distinguish phase changes, atmospheric transport, and terrestrial water pathways.
- Classify forms of condensation and explain major rainfall processes.
- Explain the importance of water cycling and assess stated forms of human disruption.
The Water Cycle as a Planetary System
The cycle moves water among the planet's different water reservoirs. The oceans are the largest reservoir and contain around 97.25 percent of the planet's water.
Different reservoirs store water as solid, liquid, or gas. Solar energy powers water movement through the cycle, while gravity assists it.
Which reservoir contains around 97.25 percent of the planet's water, and in which three states can reservoirs store water?
The oceans contain around 97.25 percent of the planet's water. Reservoirs can store water as solid, liquid, or gas.
Phase Changes and Atmospheric Transport
- Evaporation changes liquid water into gas.
- Sublimation changes solid water directly into gas without an intervening liquid phase.
- Condensation changes water from gas to liquid and releases energy.
- Deposition changes water directly from gas to solid without an intervening liquid phase.
At the dew point, air is 100 percent saturated with water vapor. Hygroscopic particles such as salt, dust, and smoke typically provide nuclei around which liquid water condenses.
Name the process for a direct solid-to-gas change and the process for a direct gas-to-solid change.
A direct solid-to-gas change is sublimation. A direct gas-to-solid change is deposition. Neither has an intervening liquid phase.
Terrestrial and Plant Water Pathways
Transpiration creates a pressure gradient that enables plants to draw water from the ground. Root hairs increase the surface area available for water absorption, and water entering roots carries dissolved minerals or salts from the soil into the plant.
- Interception interrupts the movement of water toward streams and oceans.
- Infiltration moves water from the ground surface into the ground to form soil moisture or groundwater.
- Percolation moves water vertically through rocks and soil under gravity.
- Drainage-basin runoff includes surface, subsurface, and groundwater runoff.
Identify the process when water moves from the ground surface into the ground, then identify the process when it moves vertically through rocks and soil under gravity.
Movement from the surface into the ground is infiltration. Vertical movement through rocks and soil under gravity is percolation.
Forms of Condensation and Rainfall
Dew consists of liquid water droplets deposited on cooler object surfaces such as grass blades. Frost is moisture deposited as ice crystals on cold surfaces when the dew point is below water's freezing point.
| Form | Visibility |
|---|---|
| Fog | Less than 1 kilometer |
| Mist | Between 1 and 2 kilometers |
| Haze | Between 2 and 5 kilometers |
- In convectional rainfall, surface heating raises moist air, which cools aloft, condenses into clouds, and produces precipitation.
- Orographic rain forms when mountain-forced ascent cools moist air and causes cloud formation and rainfall.
- In cyclones, cyclonic rainfall occurs when air moving rapidly toward a low-pressure center rises and generates heavy rainfall.
How does rainfall differ between the windward and leeward sides of a mountain during orographic rainfall?
Orographic rainfall produces heavy rain on the windward side and very little rain on the leeward side.
Importance of the Hydrological Cycle
The hydrological cycle transfers water from oceans to land areas and supplies organisms with freshwater needed for survival.
The cycle transfers heat from hotter areas to cooler areas through the absorption and release of latent heat.
- Water moving through rivers, streams, and rivulets erodes land.
- Flowing water deposits material along rivers and near deltas.
- Whether precipitation falls as rain or snow helps determine the type of habitat that forms.
- A greater variety of habitats supports greater biodiversity.
Which produces more flood-like conditions: substantial rainfall concentrated into a short period or the same pattern described as rainfall distributed across many months?
Concentrating substantial rainfall into a short period produces more flood-like conditions than distributing it across many months.
Human Disruption of the Hydrological Cycle
- Excessive use of surface water and groundwater contributes to water bodies drying up.
- Wetlands support groundwater recharge by providing locations for substantial infiltration.
- Concrete and tar surfaces hinder water infiltration into groundwater reservoirs.
- Sediment trapped by dams contributes to the shrinkage of deltas.
- Deforestation disrupts the hydrological cycle by removing trees that perform transpiration.
Urban heat islands can reduce rainfall by warming the upper atmosphere and interfering with the cooling needed for condensation. Global warming and climate change alter the distribution of precipitation.
Imagery from 1986 to 2019 shows the Columbia Glacier's terminus retreating and its branches becoming disconnected. Glacial meltwater entering the oceans contributes to inundation of coastal areas.
Which supports groundwater recharge through substantial infiltration: wetlands or concrete and tar surfaces? What effect do the other surfaces have?
Wetlands support groundwater recharge by providing locations for substantial infiltration. Concrete and tar surfaces hinder water infiltration into groundwater reservoirs.
Common misconceptions
Watch out: Water reservoirs store water only as liquid.
Instead: Different water reservoirs store water as solid, liquid, or gas.
Watch out: Sublimation includes an intervening liquid phase.
Instead: Sublimation changes solid water directly into gas without an intervening liquid phase.
Watch out: Concrete and tar surfaces support water infiltration into groundwater reservoirs.
Instead: Concrete and tar surfaces hinder water infiltration into groundwater reservoirs.
Lesson recap
- The hydrological cycle continuously moves water on, above, and below Earth's surface.
- Evaporation, sublimation, condensation, and deposition describe changes among liquid, solid, and gas.
- Transpiration transfers water from plants to the atmosphere, while infiltration and percolation describe movement into and through the ground.
- The cycle supplies freshwater, transfers heat, and participates in erosion and deposition.
- Water overuse, impervious surfaces, dams, deforestation, urban heat islands, and climate change alter stated parts of water cycling.