Potential Evapotranspiration (PET)

The knowledge of evapotranspiration is defined as the total quantity of water used by the vegetation growth of plant tissue and that evaporated from the adjacent soil in the area in any specific time.

Content Table

Definitions

Evaporation

It may be defined to be the loss of water particles from the water bodies and soil masses under effect of temperature and wind velocity.

Transpiration

It may be defined that the amount of water leaves a living plant through it’s leaf.

Evapotranspiration

It is the total water loss from a crop of irrigated land due to transpiration of plants during their growing period and the evaporation from the adjacent soil particles.

Potential Evapotranspiration

It may be defined as the evapotranspiration from a large vegetation covered land surface with adequate moisture at all times. In other words, it may be defined as the evapotranspiration  that occurs when the ground is completely covered by actively growing vegetation and there is no limitation in the soil moisture.

Crop-Factor

It is the ratio of the consumptive use of water to the pan evaporation. It is different for different crops and is different for the same crop for the different places.

Consumptive Use of Water

The product of the locally crop factor with potential evapotranspiration is called the consumptive use of water of evapotranspiration.

Factors Affecting Evaporation

The following factors affect the evaporation are

  • Air temperature.
  • Water temperature.
  • Relative humidity.
  • Wind velocity.
  • Exposed surface area.
  • Barometric pressure.
  • Salinity of the water.

Hence higher the temperature and wind velocity, greater the evaporation, while greater the humidity and dissolved salts, smaller the evaporation.

Factors Affecting Evapotranspiration:

The following factors affect the evapotranspiration are

  • Climatological data or factors like percentage sunshine hours, wind speed, mean monthly temperature, humidity,day length etc.
  • Crop factor like the type of the crop and the percentage growing season.
  • The moisture level in the soil.

Irrigation Scheduling

For the purpose of irrigation scheduling, it is necessary to estimate an accurate PET at any region. It is also an important index of hydrologic budgets at different spatial scales and is a critical variable for understanding regional biological process.

The yield from an agricultural land depends upon several factors but the important factor is that crops need sufficient water during its various stages of growth. Some of these water requirements are fulfilled by rain. Thus if the normal rainfall is not sufficient to met the total water requirement of the crop’s grown and the time interval of the rainfall is such that water is not available whenever plants need it, then irrigation is required.

The amount of irrigation can be estimated in several ways but the knowledge of evapotranspiration is defined as the total quantity of water used by the vegetation growth of plant tissue and that evaporated from the adjacent soil in the area in any specific time.

Research

In  a Comparison of Potential Evapotranspiration (PET) by Different Methods Under Tropical and Sub-Tropical Monsoon Region in Bangladesh conducted by Uthkal Sen Gupta, the estimation of PET by two temperature based (Hamon’s & Hargraves method) and three radiation based (Solar Radiation, Net Radiation, Priestley-Taylor method) has been attempted in tropical and sub-tropical region. A correlation in between their PET has also been attempted.

Related Articles

References

Comparison of Potential Evapotranspiration (PET) by Different Methods Under Tropical and Sub-Tropical Monsoon Region in Bangladesh

Uthkal Sen Gupta BSc

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