💧 The Water Cycle
In one sentence: Water moves between the ocean, air, land, and living things — changing form but never disappearing.
🔑 The key exam point
Global scale
- CLOSED system
- No water enters or leaves Earth
- Same water recycled forever
Local scale
- OPEN system
- Water flows in and out
- Rivers bring water in, evaporation takes it out
Earth has had the same water for billions of years — you might be drinking water a dinosaur peed in! 🦕
📦 Where water is stored
Think of these as water tanks around the planet:
- 🌊 Oceans — the BIG one (97% of all water, but salty!)
- 🧊 Ice & glaciers — frozen freshwater at poles and mountains
- 🕳️ Groundwater — underground in rocks and soil (aquifers)
- 🏞️ Rivers & lakes — surface freshwater we can see
- ☁️ Atmosphere — tiny amount, but moves a LOT of water
- 🌱 Living things — water inside plants and animals
🔄 How water moves (the flows)
Water moves between stores through these processes:
- ☀️ Evaporation — sun heats water → turns to vapour (liquid → gas)
- 🌿 Transpiration — plants release water through their leaves
- ☁️ Condensation — vapour cools → forms clouds (gas → liquid)
- 🌧️ Precipitation — water falls as rain, snow, hail
- ⬇️ Infiltration — water soaks into soil
- ⬇️⬇️ Percolation — water sinks deeper into groundwater
- 🏃 Runoff — water flows over land into rivers/sea
Memory trick: Evapotranspiration = evaporation + transpiration combined. Examiners love this word!
🏗️ How humans mess with the water cycle
- 🏙️ Cities & roads — concrete stops infiltration → more flooding
- 🪓 Deforestation — fewer trees = less transpiration + more runoff
- 🚿 Taking too much water — lowers rivers and groundwater
- 🌡️ Climate change — changes when and where rain falls
Humans change both where water is stored and how fast it moves.
📝 What examiners actually ask
- Name the stores and flows in the water cycle
- Explain why it's closed globally but open locally
- Describe how deforestation or urbanisation affects the cycle
- Draw and label a simple diagram
Exam Tips:
- Always use proper terms: say 'precipitation' not just 'rain'
- If asked about stores and flows — name BOTH and explain the connection
- Link human impacts to SPECIFIC processes (e.g., 'concrete reduces infiltration')
- Remember: closed system globally, open system locally — this is a favourite trick question!