The Water Cycle & Drainage Basin System

A Closed System

Think of the hydrological cycle like a sealed terrarium sitting on a windowsill. Nothing new water ever gets added to it, and no water ever truly leaves it — it just keeps changing form and location, over and over, forever. That's exactly what "closed system" means here: the total amount of water on Earth stays the same. It just gets constantly recycled between the atmosphere, the land surface, underground, and the oceans.

Because nothing enters or leaves the system, geographers say the hydrological cycle only has two kinds of components: stores (places where water sits still for a while) and transfers (the processes that move water from one store to another). There are no "inputs" or "outputs" — that terminology is reserved for open systems, like the drainage basin you'll meet in Topic 2.

Stores of the Hydrological Cycle

A store is simply anywhere water is held for a period of time before it moves on again — it could be held for seconds (a raindrop on a leaf) or thousands of years (deep groundwater in an aquifer). The main stores are:

• Atmosphere — water sits here as invisible water vapour or as visible water droplets in clouds.