Key Idea: Topic 4.1 is about how water moves as a global system (hydrological cycle), how it is stored and transferred (stores + flows), how drainage basins work as open systems, and why water is crucial for climate regulation.
🔁 Hydrological cycle (key processes)
- Evaporation + transpiration (evapotranspiration) move water to the atmosphere (energy absorbed)
- Condensation forms clouds (energy released)
- Precipitation returns water to land/ocean
- Infiltration (into soil) vs runoff (over land to rivers/ocean)
Energy marks: mention solar energy drives evaporation (endothermic) and condensation releases heat (exothermic).
🏦 Stores, flows & residence time
- Stores = where water is held (oceans, ice, groundwater, lakes/rivers, atmosphere)
- Flows = transfers between stores (evaporation, precipitation, runoff)
- Residence time = average time water stays in a store
- Long residence time (oceans/ice/deep groundwater) = slow to replenish → can be effectively non-renewable on human timescales
🛁 Drainage basins as systems
- Drainage basin = land area where water drains to one river system
- Watershed = boundary between basins
- Basin is an open system: inputs (precipitation, solar energy) → stores/flows → outputs (discharge, evapotranspiration, abstraction)
If asked about impacts (e.g., dams/land-use change), explain system-wide effects: flow rate, sediment, nutrients, oxygen, biodiversity downstream.
🌡️ Water and climate regulation (why water is Earth’s thermostat)
- High specific heat capacity: oceans absorb lots of heat with little temperature change
- Latent heat: evaporation cools; condensation warms
- Ocean currents redistribute heat globally
- Ice/albedo: ice reflects sunlight (cooling); melting lowers albedo (warming)
- Oceans also absorb CO₂ (carbon sink) → links to climate + acidification
1) Name 4 water-cycle processes. 2) Define residence time. 3) Explain a drainage basin as an open system. 4) Give 3 ways water regulates climate.