Hydrology & Water Resources Engineering - Vol 2 | 19. Evapotranspiration by Abraham | Learn Smarter
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19. Evapotranspiration

Evapotranspiration (ET) is a crucial component of the hydrologic cycle, integrating both evaporation and transpiration processes, influencing water demand and resource management. Understanding ET is essential for effective agricultural practices, particularly in regions with limited water resources, as it depends on various climatic, crop, and soil factors. The chapter explores methods for estimating ET, measurement techniques, and the impacts of climate change on ET dynamics.

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Sections

  • 19

    Evapotranspiration

    Evapotranspiration (ET) combines evaporation and transpiration processes, representing water loss to the atmosphere, crucial for water resource management.

    Learning Practice

  • 19.1

    Evapotranspiration – Definition And Concept

    Evapotranspiration (ET) comprises the combined processes of evaporation and transpiration, representing the total water loss from vegetated surfaces to the atmosphere.

    Learning Practice

  • 19.2

    Components Of Evapotranspiration

    Evapotranspiration consists of two main components: evaporation and transpiration, both of which are influenced by climatic and biophysical factors.

    Learning Practice

  • 19.2.1

    Evaporation (E)

    Evaporation is a key component of evapotranspiration that refers to the physical loss of water from soil, plants, and water bodies to the atmosphere.

    Learning Practice

  • 19.2.2

    Transpiration (T)

    Transpiration is a key process in the evapotranspiration cycle where plants release water vapor into the atmosphere, influenced by various botanical and environmental factors.

    Learning Practice

  • 19.3

    Factors Affecting Evapotranspiration

    Evapotranspiration is influenced by various climatic, crop, soil, and management factors that collectively determine water loss from the atmosphere.

    Learning Practice

  • 19.4

    Potential And Actual Evapotranspiration

    This section defines Potential Evapotranspiration (PET) and Actual Evapotranspiration (AET), highlighting the difference that conditions have on water loss in the atmosphere.

    Learning Practice

  • 19.5

    Methods Of Estimating Evapotranspiration

    Various methods are employed to estimate evapotranspiration (ET), classified into empirical, energy balance, and combination methods.

    Learning Practice

  • 19.5.1

    Empirical Methods

    Empirical methods are used to estimate evapotranspiration (ET) through the analysis of climatological data and regression equations.

    Learning Practice

  • 19.5.1.1

    Blaney-Criddle Method

    The Blaney-Criddle Method is an empirical approach to estimate potential evapotranspiration based on temperature and daylight hours.

    Learning Practice

  • 19.5.1.2

    Hargreaves Method

    The Hargreaves Method is a straightforward temperature-based approach for estimating evapotranspiration (ET) using maximum and minimum temperature data along with extraterrestrial radiation.

    Learning Practice

  • 19.5.1.3

    Pan Evaporation Method

    The Pan Evaporation Method estimates evapotranspiration based on measurements from a Class A evaporation pan, utilizing a pan coefficient to adjust values for various environmental conditions.

    Learning Practice

  • 19.5.2

    Energy Balance Methods

    Energy Balance Methods for estimating evapotranspiration involve the conservation of energy at the land surface.

    Learning Practice

  • 19.5.2.1

    Energy Budget Equation

    The Energy Budget Equation details the relationship between net radiation and heat fluxes at the land surface, critical for estimating evapotranspiration (ET).

    Learning Practice

  • 19.5.3

    Combination Methods

    Combination methods for estimating evapotranspiration integrate various approaches to enhance accuracy.

    Learning Practice

  • 19.5.3.1

    Penman Method

    The Penman Method combines energy balance and aerodynamic approaches to estimate evapotranspiration, providing a standard and accurate method for reference ET estimation.

    Learning Practice

  • 19.5.3.2

    Fao Penman-Monteith Method

    The FAO Penman-Monteith Method provides a standardized approach for estimating reference evapotranspiration (ET) based on climatic data and vegetation characteristics.

    Learning Practice

  • 19.6

    Measurement Techniques For Et

    This section discusses various measurement techniques for evapotranspiration (ET), including both direct and indirect methods.

    Learning Practice

  • 19.6.1

    Lysimeter

    A lysimeter is a crucial device used for accurately measuring evapotranspiration (ET) by observing mass changes in a soil-plant column.

    Learning Practice

  • 19.6.2

    Atmometer (Evaporimeter)

    The atmometer, or evaporimeter, is an instrument used to measure the rate of evaporation as a proxy for evapotranspiration.

    Learning Practice

  • 19.6.3

    Eddy Covariance System

    The Eddy Covariance System is an advanced method for measuring evapotranspiration using high-frequency wind and humidity data.

    Learning Practice

  • 19.6.4

    Bowen Ratio Energy Balance Method

    The Bowen Ratio Energy Balance Method is a technique used to measure evapotranspiration by analyzing temperature and humidity gradients.

    Learning Practice

  • 19.6.5

    Remote Sensing Techniques

    Remote sensing techniques utilize satellite data to estimate evapotranspiration (ET) over extensive areas using various vegetation indices.

    Learning Practice

  • 19.7

    Crop Coefficient (Kc) Concept

    The Crop Coefficient (Kc) is a vital parameter used to calculate the evapotranspiration (ET) of various crops based on their growth stage.

    Learning Practice

  • 19.8

    Applications Of Evapotranspiration Data

    Evapotranspiration data is crucial for various applications related to water management, agriculture, and climate studies.

    Learning Practice

  • 19.9

    Evapotranspiration Under Changing Climate

    This section discusses how climate change impacts evapotranspiration (ET) through changes in temperature, precipitation, and wind patterns.

    Learning Practice

References

Chapter_19_Evapo.pdf

Class Notes

Memorization

What we have learnt

  • Evapotranspiration is the t...
  • Factors influencing evapotr...
  • Potential ET represents max...

Final Test

Revision Tests