The Hydrological Cycle Overview

The Hydrological Cycle

• The Hydrological cycle (also known as the global water cycle or the H2O cycle) describes the storage and movement of water between Earth's spheres:
  • biosphere
  • atmosphere
  • lithosphere
  • hydrosphere
• The amount of water on Earth remains constant, but its distribution changes between three forms:
  • Liquid (water)
  • Solid (ice)
  • Gas (water vapor)

Components of the Hydrological Cycle

• Evaporation: Surface water absorbs solar radiation energy and transforms into water vapor. Oceans contribute most to this process.
• Transpiration: Plants absorb water and release it as vapor through leaves, stems, and flowers. Transpiration combines with evaporation to form evapotranspiration.
• Sublimation: Water directly transitions from a solid (ice or snow) into a gaseous (water vapor) state, bypassing the liquid form.
• Condensation: As water vapor rises and cools, it changes into liquid water droplets. These droplets form on dust particles in the air.
• Precipitation: Water falls to Earth from clouds in various forms like rain, snow, and hail. Air currents move clouds and influence precipitation patterns.
• Runoff: A portion of precipitation flows over the land's surface, moving towards rivers, lakes, or oceans as surface or sub-surface flow. Runoff occurs when precipitation exceeds soil infiltration rates.
• Infiltration: Water soaks into the soil, percolating downwards. Porosity and pore size distribution affect the infiltration rate. Infiltrated water contributes to groundwater.
• Groundwater Discharge: Water held in cracks and spaces below the ground, known as groundwater, can be tapped by wells or flow towards the surface. This process of groundwater exiting the ground is called groundwater discharge.

Processes and Pathways of the Hydrological Cycle

• The cycle begins with oceans, where water evaporates due to solar radiation.
• Water vapor forms clouds and eventually condenses to precipitate as rain, hail, or snow.
• Some precipitation evaporates back into the atmosphere, while some reaches the ground.
• Ground infiltration replenishes soil moisture and raises the water table.
• Vegetation releases transpired water back to the atmosphere.
• Runoff flows over the land, eventually reaching rivers, lakes, and finally oceans.
• The process continues as cool air blowing over oceans carries water molecules, forming more water vapor and clouds that ultimately release precipitation.