Hydrology & Water Resources Engineering - Vol 2 | 20. Measurement of Evapotranspiration by Abraham | Learn Smarter
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20. Measurement of Evapotranspiration

Evapotranspiration encompasses the combined processes of evaporation and transpiration, playing a vital role in the hydrologic cycle and water resource management. Accurate measurement methods, both direct and indirect, include lysimeters, water balance, and remote sensing techniques, which provide insights into water balance, irrigation planning, and drought assessment. Various factors such as climate and plant characteristics influence evapotranspiration rates, which can be quantified using mathematical models and empirical methods.

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Sections

  • 20

    Measurement Of Evapotranspiration

    Evapotranspiration is the process combining evaporation and transpiration, crucial for water resource management.

    Learning Practice

  • 20.1

    Evapotranspiration – Basic Concepts

    Evapotranspiration combines evaporation and transpiration processes, critical for water management and hydrology.

    Learning Practice

  • 20.2

    Factors Affecting Evapotranspiration

    Multiple climatic, soil, and plant-related factors influence the process of evapotranspiration.

    Learning Practice

  • 20.3

    Methods Of Measurement Of Evapotranspiration

    This section outlines both direct and indirect methods for measuring evapotranspiration, essential for effective water resource management.

    Learning Practice

  • 20.3.1

    Direct Methods

    Direct methods measure evapotranspiration through actual field observations, providing precise data on water loss.

    Learning Practice

  • 20.3.1.a

    Lysimeter Method

    The lysimeter method involves using a specialized tank to measure evapotranspiration by monitoring changes in weight due to water loss.

    Learning Practice

  • 20.3.1.b

    Field Experimental Plots

    Field experimental plots utilize controlled water applications and observe resulting plant growth and soil moisture changes to calculate evapotranspiration.

    Learning Practice

  • 20.3.2

    Indirect Methods

    Indirect methods utilize meteorological and empirical data to estimate evapotranspiration (ET).

    Learning Practice

  • 20.3.2.a

    Water Balance Method

    The Water Balance Method estimates evapotranspiration (ET) using a continuity equation that accounts for precipitation, runoff, deep percolation, and change in soil water storage.

    Learning Practice

  • 20.3.2.b

    Energy Balance Method

    The Energy Balance Method estimates evapotranspiration (ET) based on the conservation of energy principle, taking into account net radiation, soil heat flux, sensible heat flux, and latent heat flux.

    Learning Practice

  • 20.3.2.c

    Aerodynamic Method

    The Aerodynamic Method estimates evapotranspiration using wind speed and vapor pressure differences.

    Learning Practice

  • 20.3.2.d

    Combination Method (Penman Equation)

    The Combination Method, illustrated by the Penman Equation, integrates both energy balance and aerodynamic principles to estimate evapotranspiration effectively.

    Learning Practice

  • 20.4

    Empirical Methods

    Empirical methods utilize well-established equations to estimate evapotranspiration when direct measurement data is absent.

    Learning Practice

  • 20.4.1

    Blaney-Criddle Method

    The Blaney-Criddle Method is an empirical formula used to estimate evapotranspiration (ET) based on temperature and daylight hours.

    Learning Practice

  • 20.4.2

    Thornthwaite Method

    The Thornthwaite Method estimates potential evapotranspiration (PET) based on mean monthly temperature and day length.

    Learning Practice

  • 20.4.3

    Hargreaves Method

    The Hargreaves Method is a simplified approach for estimating evapotranspiration using temperature data, and is regarded as being more accurate than the Thornthwaite Method.

    Learning Practice

  • 20.5

    Measurement Of Pan Evaporation

    Pan evaporation measurements are crucial for estimating reference evapotranspiration using evaporation pans.

    Learning Practice

  • 20.6

    Remote Sensing And Et Estimation

    Remote sensing offers advanced tools to estimate evapotranspiration (ET) using satellite-based sensors.

    Learning Practice

  • 20.7

    Use Of Lysimeters In India

    Lysimeters in India are critical tools used in agriculture to measure evapotranspiration, helping to develop crop coefficients for various agro-climatic zones.

    Learning Practice

  • 20.8

    Crop Coefficients And Reference Et (Et₀)

    This section discusses the computation of reference evapotranspiration (ET₀) using crop coefficients and the significance of the FAO Penman-Monteith method.

    Learning Practice

References

Chapter_20_Measu.pdf

Class Notes

Memorization

What we have learnt

  • Evapotranspiration is a key...
  • Measurement of evapotranspi...
  • Both direct and indirect me...

Final Test

Revision Tests