Climate Change Impact on India and World – International Reports, Key Observations, etc.

Role of Evapotranspiration in Earth’s Dynamic Processes


From UPSC perspective, the following things are important :

Prelims level: Evapotranspiration, Water Cycle

Mains level: NA



Central Idea:  Evapotranspiration is a key process in Earth’s dynamic systems, impacting the movement of water and nutrients, influencing the water cycle, and providing crucial information for farmers to manage irrigation and water resources effectively.

Understanding Evapotranspiration

  • Definition: Evapotranspiration refers to the movement of water from terrestrial surfaces into the atmosphere and is a crucial part of the planet-wide water cycle.
  • Water cycle and its connection to evapotranspiration: Evapotranspiration is an amalgamation of evaporation (water loss from soil) and transpiration (water movement and loss by plants), both of which contribute to the overall movement of water in the water cycle.
  • Breakdown of the term: Evapotranspiration encompasses the movement of water upward through plants and its subsequent loss into the air from exposed plant parts.

Factors affecting Evapotranspiration

  • Rate of evapotranspiration: Several factors impact the rate of evapotranspiration, including solar radiation, day length, soil moisture levels, ambient temperature, wind conditions, and the amount of water vapour already present in the air.
  • Insolation and its effect: The intensity of solar radiation directly affects the rate of evapotranspiration, as it provides the energy needed to evaporate water from terrestrial surfaces.
  • Role of day length: The length of the day, soil moisture content, ambient temperature, wind patterns, and the moisture content of the air all contribute to the rate at which evapotranspiration occurs.

Historical significance of evapotranspiration

  • Origin and age of the term: The term “evapotranspiration” has been in use for at least 86 years and was initially published with a hyphenated form.
  • Contribution of Charles Warren Thornthwaite in 1944: Thornthwaite, an American climatologist, defined and popularized the term “evapotranspiration” in 1944.
  • Relevance for farmers in estimating water needs for crops: Even today, evapotranspiration remains significant for farmers who utilize it to estimate the amount of water required to irrigate their crops effectively.

Back2Basics: Water Cycle

  • The water cycle, also known as the hydrological cycle, is the continuous movement and circulation of water on, above, and below the Earth’s surface.
  • Stages of the Water Cycle include:
  1. Evaporation: The process by which water changes from a liquid state to a gaseous state, rising into the atmosphere.
  2. Condensation: The cooling of water vapor in the atmosphere, causing it to change from a gaseous state back to a liquid state, forming clouds.
  3. Precipitation: When condensed water droplets combine and fall from the atmosphere as rain, snow, sleet, or hail.
  4. Runoff: The movement of water on the Earth’s surface, flowing into streams, rivers, lakes, and eventually into the oceans.
  5. Infiltration: The process by which water seeps into the ground and becomes groundwater.
  6. Transpiration: The release of water vapor from plant surfaces into the atmosphere.


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