The Water Cycle Explained for KS3 Geography

The water cycle (also called the hydrological cycle) is the continuous movement of water between the land, the oceans and the atmosphere. Water evaporates from the surface, rises and cools to form clouds, falls as precipitation, and flows back to the sea — then the process repeats endlessly. No water is created or destroyed; it is constantly recycled through the same system.

Why does the water cycle matter?

The water cycle distributes freshwater across the planet, regulates temperature, shapes river systems and determines where plants can grow. Without it, rainfall would be unevenly distributed and the land surface would rapidly become too dry or too waterlogged to support life as we know it.

For KS3 geography, understanding the water cycle also underpins topics including rivers and flooding, drought and water scarcity, and the impacts of deforestation and urbanisation on local water systems.

The main stages of the water cycle

1. Evaporation

Evaporation is the process by which liquid water is converted into water vapour (gas) and enters the atmosphere. It happens from the surface of oceans, lakes, rivers and puddles when solar energy heats the water. Approximately 86 per cent of all water that enters the atmosphere does so through evaporation from the oceans.

The rate of evaporation increases with higher temperature, lower humidity, and stronger winds — which is why hot, windy desert regions experience high evaporation rates despite having little rainfall.

2. Transpiration and evapotranspiration

Plants absorb water through their roots and release water vapour through tiny pores in their leaves called stomata. This process is called transpiration. Because evaporation from soil and transpiration from plants are difficult to separate in practice, geographers often refer to evapotranspiration — the combined total water lost to the atmosphere from both processes.

Forests play a critical role in the water cycle: a single large tree can transpire hundreds of litres of water per day. Large-scale deforestation reduces evapotranspiration, which in turn reduces local rainfall and can disrupt the regional water cycle — a key argument in debates about deforestation in the Amazon.

3. Condensation and cloud formation

As water vapour rises into cooler parts of the atmosphere, it cools below its dew point — the temperature at which the air can no longer hold all the water vapour — and condenses around tiny particles of dust or sea salt to form water droplets. Billions of these microscopic droplets together form a cloud.

Different cloud types form at different altitudes and under different atmospheric conditions, and they indicate different types of coming weather. At KS3, students are usually expected to understand the basic principle that warm, moist air rising = cloud formation = potential precipitation.

4. Precipitation

Precipitation is any form of water falling from clouds to the Earth's surface. It includes:

Rain — the most common form in the UK

Snow — precipitation that freezes before reaching the ground, common in upland areas and during cold spells

Sleet — a mixture of rain and snow

Hail — balls of ice formed by strong updraughts in storm clouds repeatedly pushing water droplets through the freezing layer

In the UK, the west coast receives significantly more rainfall than the east because prevailing westerly winds carry moisture from the Atlantic, and the mountains of Wales, the Lake District and Scotland force the air upwards — a process called relief (orographic) rainfall — causing heavy precipitation. The leeward (east) side of these uplands is drier — this is the rain shadow effect.

5. Surface run-off and overland flow

When precipitation falls on the land, several things can happen to it. It can soak into the ground (infiltration), be absorbed by plant roots, or flow across the surface as run-off (also called overland flow). Run-off collects into streams and rivers, which ultimately carry the water back to the sea — completing the cycle.

The proportion of water that becomes run-off versus infiltrating the ground depends on:

Soil type: sandy soils allow rapid infiltration; clay soils do not.

Gradient: steep slopes increase run-off speed.

Ground cover: bare, hard, or frozen ground prevents infiltration and increases run-off.

Land use: urban areas with tarmac and concrete surfaces dramatically increase run-off rates, which is why flooding risk is higher in cities. This is directly relevant to discussions of river management and flood prevention at KS3.

6. Groundwater flow and the water table

Water that infiltrates the soil and rocks slowly percolates downward until it reaches saturated rock — the water table. Below this level, all pores and cracks in the rock are filled with water (groundwater). Groundwater flows very slowly through permeable rocks called aquifers and eventually emerges at the surface as springs or discharges into rivers and the sea.

Aquifers are critical freshwater resources: in England, the Chalk aquifer beneath much of the South East provides a significant proportion of the region's drinking water. The Environment Agency monitors aquifer levels to manage water resources sustainably.

How human activity affects the water cycle

Human actions can significantly alter the natural water cycle:

Deforestation reduces transpiration and interception, increases surface run-off, and can reduce local rainfall.

Urbanisation replaces permeable land with impermeable surfaces, increasing the speed and volume of surface run-off and raising flood risk downstream.

Irrigation and water abstraction remove water from rivers and aquifers faster than they can naturally recharge, lowering water tables and reducing river flow.

Climate change is altering precipitation patterns globally — intensifying rainfall events in some regions, extending droughts in others, and accelerating glacial melt that affects long-term river flows.

Frequently asked questions

What is the order of the water cycle?

The water cycle does not have a fixed starting point — it is continuous — but a convenient way to trace it is: solar energy heats water at the surface → water evaporates and rises → water vapour condenses into clouds → precipitation falls → water flows over or through the land as run-off or infiltration → rivers carry water back to the sea → the cycle continues.

What is the difference between evaporation and transpiration?

Evaporation is the conversion of liquid water into water vapour from any open water surface (oceans, lakes, puddles). Transpiration is the release of water vapour specifically by plants through their leaves. Both add water to the atmosphere; together they are called evapotranspiration. The distinction matters because deforestation primarily reduces transpiration, not evaporation from open water.

What is infiltration in the water cycle?

Infiltration is the process by which water soaks from the surface into the soil and rock below. It is the opposite of surface run-off. High rates of infiltration mean less water reaches rivers quickly, reducing flood risk. Low rates (on clay soils or urban surfaces) mean more run-off and faster response to rainfall in river systems, increasing flood risk.

How does deforestation affect the water cycle?

Deforestation reduces transpiration (less water is released by plants), reduces interception (leaves no longer catch and slowly release rainfall), and increases surface run-off (bare ground infiltrates less water). The combined effect is that more water reaches rivers rapidly after rain, increasing flood risk, while long-term rainfall in the region may decrease because there is less evapotranspiration to maintain moisture in the local atmosphere.

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