Evapotranspiration Explained
Understanding how much water crops require is one of the most important aspects of irrigation management. One of the key measurements used to estimate crop water demand is evapotranspiration.
Evapotranspiration, often abbreviated as ET, describes the combined process of water evaporating from the soil surface and being released by plants through transpiration. Together these processes represent the total amount of water lost from the soil–plant system to the atmosphere.
By measuring evapotranspiration, farmers can estimate how much water crops are using and determine how much irrigation is required to maintain optimal growing conditions.
The Components of Evapotranspiration
Evapotranspiration consists of two main processes.
Evaporation
Evaporation occurs when water from soil, irrigation or rainfall turns into water vapour and enters the atmosphere.
Factors that influence evaporation include:
temperature
solar radiation
wind speed
humidity
Higher temperatures and stronger winds generally increase evaporation rates.
Transpiration
Transpiration is the process by which plants release water vapour through tiny openings in their leaves called stomata.
As plants absorb water through their roots, some of that water is used for growth while the remainder is released into the atmosphere.
Together evaporation and transpiration determine the total water loss from a crop system.
Measuring Evapotranspiration with Weather Stations
Agricultural weather stations provide the environmental measurements required to estimate evapotranspiration.
Typical weather station sensors measure:
air temperature
humidity
wind speed
solar radiation
Using these measurements, evapotranspiration models can estimate how much water crops are losing each day.
These calculations help farmers determine how much water must be replaced through irrigation.
Using Evapotranspiration for Irrigation Scheduling
Evapotranspiration data can be used to guide irrigation scheduling by estimating daily crop water use.
For example, if a crop loses 5 millimetres of water through evapotranspiration during a day, irrigation systems can be adjusted to replace that amount.
This approach helps maintain optimal soil moisture levels without overwatering.
When evapotranspiration data is combined with soil moisture monitoring, farmers gain a highly accurate understanding of crop water demand.
Why Evapotranspiration Matters for Precision Agriculture
Evapotranspiration measurements play an important role in modern precision agriculture systems.
By monitoring environmental conditions and crop water demand, farmers can:
improve irrigation efficiency
reduce water consumption
optimise crop growth
improve yield consistency
Understanding evapotranspiration helps farmers move from reactive irrigation decisions to data-driven water management strategies.