The Water Cycle
The global hydrological (water) cycle is a closed system in which water continuously circulates between the oceans, atmosphere, and land without any water entering or leaving the planet. Solar energy drives evaporation and transpiration into the atmosphere, while condensation and gravity return water to the surface as precipitation, infiltration, and river runoff.
- Evaporation
- The process by which liquid water gains enough heat energy (mainly from the Sun) to change into water vapour and rise into the atmosphere. Most evaporation occurs from the oceans, which cover about 71% of Earth's surface.
- Condensation
- The change of water vapour back into tiny liquid droplets as air cools and reaches its dew point. This is how clouds and fog form, as vapour condenses around microscopic particles called condensation nuclei.
- Precipitation
- Water that falls from clouds to the surface as rain, snow, sleet, or hail, once droplets combine and grow heavy enough to overcome updrafts. It is the main way water returns from the atmosphere to the land and oceans.
The Water Cycle: Flood Hydrographs, Plate Margins & Global Systems
Test how land use changes storm hydrograph lag times, compare plate boundaries, and inspect global atmospheric cells and the Demographic Transition Model.
Key Concepts & Exam Definitions (5)
- Evaporation
- The process by which liquid water gains enough heat energy (mainly from the Sun) to change into water vapour and rise into the atmosphere. Most evaporation occurs from the oceans, which cover about 71% of Earth's surface.
- Condensation
- The change of water vapour back into tiny liquid droplets as air cools and reaches its dew point. This is how clouds and fog form, as vapour condenses around microscopic particles called condensation nuclei.
- Precipitation
- Water that falls from clouds to the surface as rain, snow, sleet, or hail, once droplets combine and grow heavy enough to overcome updrafts. It is the main way water returns from the atmosphere to the land and oceans.
- Transpiration
- The release of water vapour from plants into the atmosphere, mostly through tiny pores in leaves called stomata. Combined with evaporation from soil and water surfaces, it is referred to as evapotranspiration.
- Runoff and Infiltration
- Runoff is precipitation that flows over the land surface into streams, rivers, lakes, and oceans, while infiltration is water soaking down into the soil and rock to replenish groundwater. Together they control how water moves back toward the sea.
Quick-Fire Flashcards (5)
Click any card to check the answer, then mark it as Known to track your progress.
What is the main source of energy that drives the water cycle?
Name the four core processes of the water cycle.
What is the difference between evaporation and transpiration?
How do clouds form in the water cycle?
What is sublimation in the context of the water cycle?
Exam-Style Questions & Mark Schemes (3)
Write or think through your answer first, then click Check Mark Scheme to see the exact points examiners award marks for.
- Q1
Explain why the water cycle is described as a 'closed system' at the global scale.
Click “Check Mark Scheme” to compare your answer, It is closed because the total amount of water on Earth stays roughly constant; water is not created or destroyed but continuously recycled between the oceans, atmosphere, and land. It only changes state (solid, liquid, gas) and location, rather than the overall quantity changing.
- Q2
A student observes dew forming on grass on a cold morning. Which process of the water cycle does this demonstrate, and why does it happen?
Click “Check Mark Scheme” to compare your answer, This demonstrates condensation. Overnight the ground and air cool, and when the air temperature drops to its dew point, water vapour can no longer stay as a gas, so it condenses into liquid droplets on cool surfaces like grass.
- Q3
Describe how deforestation could disrupt the water cycle in a region.
Click “Check Mark Scheme” to compare your answer, Removing trees reduces transpiration, so less water vapour enters the atmosphere, which can lower local humidity and rainfall. Fewer roots and less canopy also reduce infiltration and increase surface runoff, raising the risk of flooding, soil erosion, and reduced groundwater recharge.
Common Exam Questions (3)
What are the four main processes of the water cycle?
The four main processes are evaporation (liquid water heated by the Sun turns into water vapour), condensation (rising water vapour cools to form cloud droplets), precipitation (water falls as rain, snow, sleet, or hail), and collection/runoff (water flows over land or infiltrates soil to return to rivers and oceans).
What drives the water cycle?
Thermal energy from the Sun powers evaporation and transpiration, while gravity pulls precipitation to the ground and drives surface runoff, infiltration, and groundwater flow back to the oceans.
What is transpiration?
Transpiration is the evaporation of water from the internal surfaces of plant leaves and its diffusion as water vapour into the atmosphere through microscopic pores called stomata. Combined with evaporation from soil and water bodies, it is known as evapotranspiration.
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