Overview

• The Water Cycle, also known as the hydrologic cycle, describes the continuous movement of water on, above, and below the surface of the Earth.
• Water is vital for all forms of life and it exists in the Earth’s system in all three states: solid, liquid, and gas.

Key Stages in the Water Cycle

Evaporation and Transpiration

• Evaporation is the process by which water changes from a liquid to a gas or vapour, predominantly from oceans and seas, but also from other bodies of water and other surfaces.
• Plants also lose water to the atmosphere through transpiration.

Condensation and Precipitation

• Once water vapour resides in the atmosphere, it can condense to form clouds or fog in a process called condensation.
• The condensed water droplets in the clouds can combine into larger droplets and when they are heavy enough, they fall from the sky as precipitation.

Runoff and Infiltration

• Some of the water falling as precipitation may evaporate again, some might be taken up by plants, but the majority will either infiltrate into the ground in a process called infiltration, or it may flow over the surface as runoff and end up in the sea, allowing the cycle to begin anew.

Role of Humans and Impact on the Water Cycle

• Human activities like urbanisation, deforestation, and climate change have considerable effects on the water cycle.
• Urbanisation changes the landscape which can affect runoff and infiltration processes.
• Deforestation reduces transpiration, which can lead to lower rainfall levels in the surrounding area.
• Climate change caused primarily by human activities is expected to cause intense rainfall and prolonged droughts, disrupting the natural balance of the water cycle.

Key Points to Remember

• The Water Cycle is a dynamic system that continuously recycles Earth's water supply.
• Understanding of the water cycle helps in managing our water resources and predicting water availability.
• It is important to understand how human activities impact the water cycle and how we can mitigate those impacts, including through water conservation, reforestation, and the use of sustainable building materials.