The Hydrological Cycle
The Hydrological Cycle
Overview
- The hydrological cycle describes how water moves around the Earth, from the atmosphere to the Earth and back again.
- This cycle is also known as the water cycle.
- It includes a series of stages: evaporation, transpiration, condensation, precipitation, overland flow, throughflow and groundwater flow.
Evaporation
- Evaporation is when the sun heats up water on the surface of rivers, lakes, or oceans, turning it into vapour that rises into the atmosphere.
- Evaporation is a major method through which water enters the atmosphere.
Transpiration
- Transpiration is another way water enters the atmosphere; this is when water is absorbed by plants and then released through small pores called stomata.
- Together, evaporation and transpiration are sometimes referred to as evapotranspiration.
Condensation
- Condensation is the process through which water vapour in the atmosphere cools down and forms liquid water droplets, which cluster together to create clouds.
- Condensation is a vital stage - without it, water could not return to the Earth's surface.
Precipitation
- Precipitation refers to any form of water - solid or liquid - that falls from the atmosphere to the Earth's surface. This includes rain, snow, sleet, and hail.
- Precipitation occurs when condensed water droplets in clouds become too heavy and fall to the ground.
- The amount and type of precipitation that occurs is greatly influenced by the local weather and climate conditions.
Overland Flow
- The overland flow (or surface runoff) happens when water from precipitation flows over the Earth's surface. This happens when the land is unable to absorb the water quickly enough due to its being saturated or having an impermeable layer.
- Overland flow is a significant contribution to river flow, and it can lead to soil erosion if not managed properly.
Throughflow
- Throughflow is when water travels downwards through the underlying soil layers towards the riverbeds.
- This water movement is influenced by the soil structure, vegetation, and slope steepness.
Groundwater Flow
- Groundwater flow takes place when water infiltrates deeper and fills up the spaces and cracks in permeable rock formations, creating water-bearing rocks known as aquifers.
- This water can slowly move towards lakes, oceans, and rivers or can be brought up to the surface through natural springs.