Hydrological Cycle Study Notes

Hydrological Cycle Introduction

Learning Objectives

  • Illustrate the hydrological cycle and discuss its significance to plant growth and development.

  • Explain the role of precipitation and condensation in the water cycle.

  • Describe how transpiration from plants affects the water cycle.

  • Distinguish between runoff and groundwater.

Key Terms

  • Condensation: The process by which water vapor in the air is changed into liquid water.

  • Evaporation: The process by which water changes from a liquid to a gas or vapor.

  • Evapotranspiration: The sum of evaporation from the land surface plus transpiration from plants.

  • Groundwater: The water beneath Earth's surface in soil pore spaces and in the fractures of rock formations.

  • Hydrologic Cycle: The continuous circulation of water from land and sea to the atmosphere and back again.

  • Precipitation: The process by which water droplets fall to Earth as rain, hail, or snow.

  • Runoff: The flow of water downhill across saturated or impervious surfaces above ground.

  • Transpiration: The process by which water is taken up by plants and released into the atmosphere.

The Water Cycle

  • The water cycle has no definitive starting point; however, most of Earth's water exists in the oceans, making it a practical starting location for understanding the cycle.

  • Hydrologic Cycle Definition: The continuous circulation of water between land, sea, and the atmosphere.

  • Driving Force: The sun heats water in the oceans, leading to water changing from liquid to vapor through the process of evaporation.

  • A smaller amount of moisture is added as ice and snow, which can undergo sublimation, changing directly from solid to vapor.

Transpiration

  • Similar to human respiration, plants release water vapor, though the more precise term is transpiration.

  • Transpiration accounts for about 10% of the moisture in the atmosphere, while oceans and other water bodies supply nearly 90%, with a minimal amount from sublimation.

  • Evapotranspiration: This process sums the total evaporation from land surfaces and transpiration from plants, impacting the hydrological cycle significantly.

Condensation Process

  • Definition of Condensation: The transformation of water vapor into liquid water.

  • The vapor rises, where cooler temperatures lead to condensation, forming clouds.

  • Clouds play a crucial role in regulating Earth's energy flow by:

    • Reflecting incoming solar radiation to space.

    • Retaining outgoing terrestrial radiation near the Earth’s surface