Teaching focus
Level: A-level Geography
Topics: Water cycle; precipitation; ocean–atmosphere interactions; ENSO; regional water availability; global atmospheric connections.
Use the simulation to move students from describing rainfall patterns to explaining the processes that produce them. Keep returning to the relationship between moisture supply, movement of air, ascent, cooling, condensation and precipitation.
Learning objectives
Students should be able to:
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Describe the usual relationship between easterly trade winds, warm surface water and rainfall across the tropical Pacific.
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Explain how weakening trade winds and changing ocean conditions accompany the development of El Niño.
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Explain precipitation formation using evaporation, moisture transport, convergence, uplift, adiabatic cooling and condensation.
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Compare rainfall responses in Australia/Indonesia, the central/eastern Pacific and contrasting parts of South America.
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Connect changes in precipitation to soil moisture, runoff, river flow and vegetation stress.
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Explain how atmospheric teleconnections produce rainfall effects beyond the Pacific.
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Recognise that rainfall responses vary between places, seasons and individual events.
Prior understanding
Students should already understand evaporation, condensation and precipitation, and recognise precipitation as an input to a drainage basin. Briefly revisit soil-water storage, infiltration and runoff before using the regional comparisons.
Introduce convergence as air coming together and subsidence as descending air. Explain adiabatic cooling as cooling caused by expansion as rising air encounters lower pressure.
Suggested teaching sequence
- Establish the neutral Pacific pattern
Begin with Pacific mechanism, select Neutral, and identify the western and eastern sides of the basin.
Work through the four process buttons: Trade winds, Ocean response, Making rain and Rainfall shifts. Ask students to describe the arrows before explaining their significance.
Establish that easterly trade winds blow towards the west and help accumulate warm surface water in the western Pacific. Colder water rises towards the surface in the eastern Pacific through upwelling.
Use the cloud and upward arrows to construct the precipitation sequence:
Evaporation supplies water vapour → moist air converges and rises → air expands and cools → condensation forms cloud droplets → droplets or ice particles grow → precipitation falls.
Ask students to distinguish the upward movement of air from the downward movement of precipitation. Remind them that water vapour is invisible; visible clouds contain liquid droplets and/or ice crystals.
- Predict and observe El Niño developing
Before pressing Develop El Niño, ask students to predict what might happen if the easterly trade winds weaken.
Pause at several stages and track three changes:
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The progressive fading of the trade-wind arrows.
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The redistribution of warm surface water and changing thermocline.
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The movement of the main rising-air and rainfall zone.
Explain that the eastern thermocline deepens as the warm surface layer extends eastwards, reducing the supply of cold water to the surface. The main tropical convective rain zone becomes displaced towards the central/eastern Pacific.
Keep the explanation focused on linked ocean and atmospheric changes. The simulation presents a teaching sequence, but El Niño is a coupled system in which winds, ocean temperatures and circulation influence one another.
- Compare regional water-cycle responses
Open Regional water cycle. Begin with Australia & Indonesia, where land is on the left and the Pacific is on the right.
Explain the visual conventions before changing the slider:
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Teal arrows show near-surface air movement and ascent.
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Dashed atmospheric paths show returning and descending air.
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Blue rainfall and runoff markings show water moving to the surface and returning towards the sea.
Ask students to follow the atmospheric circulation first, then trace the water transfers separately.
Use all four regional comparisons:
These are regional tendencies. Australian drying is particularly associated with winter and spring; the coastal and northern South American examples shown emphasise December–February.
A useful recording task is:
What changes in the atmosphere? → What happens to precipitation? → What could happen to water stores and transfers?
Encourage conditional wording such as can reduce, may increase and becomes more likely. Catchment responses also depend on antecedent conditions, soils, drainage and land cover.
- Use the forest changes to connect processes and impacts
Return to the Australia/Indonesia comparison and watch the vegetation change as the selected state develops.
Ask students to explain the sequence from lower precipitation to declining soil moisture and drier vegetation. The fire animation represents a possible outcome if ignition occurs. El Niño-related drying can allow fires to spread more readily, but El Niño does not itself ignite the forest.
Use this to distinguish a physical process, an environmental condition and a hazard:
Reduced precipitation → drier vegetation and fuel → increased fire risk if ignited.
- Extend from regional to global effects
Open Global connections and introduce a teleconnection as a relationship through which changes in one region influence weather or climate elsewhere.
Use the southern United States example to show how Pacific changes can alter the jet stream and winter rainfall far from the main tropical convective zone.
Students should then select three contrasting regions and record:
Use the seasonal filter before making comparisons. The “all seasonal examples” map combines responses from different times of year.
Important model conventions and misconceptions
Evaporation continues in the west.
Reduced rainfall should not be explained as “the ocean stops evaporating”. Direct students back to moisture convergence, uplift and cooling.
Disappearing trade arrows represent weakening winds.
The four arrows fade for visual clarity. Their disappearance does not mean that all surface winds cease.
The reversed western regional circulation is illustrative.
The selected panel shows one possible local circulation response. It should not be presented as a necessary reversal of all Pacific trade winds or as a daily sea breeze.
The main cloud represents a convective region.
It is not one individual cloud travelling across the entire Pacific. Likewise, removing the small edge clouds at full development does not mean that those regions receive no rain. Keep the coastal Ecuador/northern Peru comparison in view when explaining this simplification.
The forest represents tropical Indonesia.
The combined Australia/Indonesia scene does not imply that all of Australia is covered by rainforest. The diagram combines neighbouring regions schematically.
The slider is conceptual.
Its position is not an ENSO index, a measured temperature anomaly, a rainfall total or a real event timeline. Arrow speeds, raindrop numbers and changing water stores are qualitative illustrations.
A rainfall tendency is not a guaranteed drought or flood.
Individual El Niño events differ, and event strength alone does not determine the severity of Australian rainfall impacts.
Discussion and assessment questions
QuestionExpected reasoning**Why does rising moist air produce cloud and potentially precipitation?**Rising air expands and cools. Condensation forms droplets or ice crystals, which must grow sufficiently before falling as precipitation.**Why can western rainfall decrease while ocean evaporation continues?**Moisture availability alone is insufficient: reduced convergence and ascent, together with subsidence, can suppress cloud development.**Why is “South America becomes wetter” too general?**Students should identify contrasting coastal and northern regional responses rather than describe the continent as a single rainfall zone.**Why must a global rainfall comparison name the season?**The map shows seasonal tendencies, so effects displayed together may occur at different times of year.**What information is missing if we want to predict an actual wildfire?**An ignition source, fuel conditions, local weather and land-management factors.
Suggested written task
Explain how El Niño can change precipitation and other water-cycle processes in two contrasting regions.
Ask students to name both regions, explain the atmospheric processes, connect precipitation to at least one water store or transfer, and acknowledge variation between events.
For support, provide the vocabulary trade winds, warm surface water, convergence, ascent, cooling, condensation, precipitation, subsidence, soil moisture and runoff.
For extension, ask students to evaluate why a schematic ENSO model can help explain regional patterns but cannot, by itself, predict the severity of drought or flooding in a particular catchment.