IB Environmental systems and societies 4.1A Hydrological Cycle Notes

Hydrological cycle: a closed system of water stores and flows powered by solar energy and gravity

Solar energy drives the upward movements of water: evaporation and transpiration.

Heat gives water molecules enough energy to change from liquid to vapour and enter the atmosphere.

Gravity drives the downward movements: precipitation falls, and water flows downhill as runoff, infiltration and streamflow.

This downhill flow returns water from land to the oceans, completing the cycle.

Definition

Evaporation

Evaporation is the transformation of liquid water into vapour due to solar heating.

Definition

Transpiration

Transpiration is the release of water vapour by plants into the atmosphere.

Analogy

The Sun is the engine that lifts water into the sky, and gravity is the return system that brings it back down.

System behaviour: water is conserved globally, closed for matter but open for energy

The global hydrological cycle is a closed system for matter: water is neither added to nor lost from Earth, so the total volume stays constant.

It is an open system for energy: solar radiation enters and heat is lost, and this energy drives every flow.

The system is built from stores (reservoirs of water) linked by flows (movements between them).

Flows are either transfers that change a store's location or transformations that change water's state.

Definition

Stores

Stores are places where water accumulates or is held temporarily, such as oceans, glaciers, lakes, or groundwater.

Definition

Flow

A flow is the movement of water between stores either as a transfer or a transformation.

Stores: oceans hold almost all of Earth's water, while accessible freshwater is a tiny fraction

Earth's water sits in six main stores, which differ in volume, state and residence time.

Oceans: ~96.5% of all water, saline, the largest reservoir.

Ice caps and glaciers: ~1.7%, frozen freshwater with a long residence time.

Groundwater: ~1.7%, the largest accessible store of liquid freshwater, held in aquifers.

Surface freshwater (lakes and rivers): <0.02%, tiny but the most accessible and fastest-responding store.

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Note

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Tip

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IB Environmental systems and societies 4.1A Hydrological Cycle Notes

Hydrological cycle: a closed system of water stores and flows powered by solar energy and gravity

System behaviour: water is conserved globally, closed for matter but open for energy

Stores: oceans hold almost all of Earth's water, while accessible freshwater is a tiny fraction

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

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Hydrological cycle: a closed system of water stores and flows powered by solar energy and gravity

System behaviour: water is conserved globally, closed for matter but open for energy

Stores: oceans hold almost all of Earth's water, while accessible freshwater is a tiny fraction

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

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Topic 1: Foundation 3 subtopics

Topic 2: Ecology5 subtopics

Topic 3: Conservation and biodiversity3 subtopics

Topic 4: Water4 subtopics

Topic 5: Land2 subtopics

Topic 6: Atmosphere and climate change4 subtopics

Topic 7: Natural resources3 subtopics

Topic 8: Human populations and urban systems3 subtopics

HL lenses 3 subtopics

IB Environmental systems and societies 4.1A Hydrological Cycle Notes

Topic 1: Foundation 3 subtopics

Topic 2: Ecology5 subtopics

Topic 3: Conservation and biodiversity3 subtopics

Topic 4: Water4 subtopics

Topic 5: Land2 subtopics

Topic 6: Atmosphere and climate change4 subtopics

Topic 7: Natural resources3 subtopics

Topic 8: Human populations and urban systems3 subtopics

HL lenses 3 subtopics

Hydrological cycle: a closed system of water stores and flows powered by solar energy and gravity

System behaviour: water is conserved globally, closed for matter but open for energy

Stores: oceans hold almost all of Earth's water, while accessible freshwater is a tiny fraction

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account

Hydrological cycle: a closed system of water stores and flows powered by solar energy and gravity

System behaviour: water is conserved globally, closed for matter but open for energy

Stores: oceans hold almost all of Earth's water, while accessible freshwater is a tiny fraction

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account