Evapotranspiration, abbreviated as ET, is the combined process by which water is transferred from the Earth's surface to the atmosphere through two mechanisms, evaporation and transpiration. Evaporation is the physical process in which liquid water from surfaces such as soil, lakes, rivers, and wet vegetation changes into water vapor and enters the air. Transpiration is the biological process by which plants absorb water through their roots, transport it through their tissues, and release it as water vapor through tiny openings in their leaves called stomata.
Together, evapotranspiration represents the total water loss from the Earth's surface to the atmosphere. Evaporation and transpiration occur simultaneously and both processes depend on solar radiation, air temperature, relative humidity (vapor pressure deficit) and wind speed. Transpiration rate is also influenced by crop characteristics, environmental aspects and cultivation practices. Different kinds of plants may have different transpiration rates. Not only the type of crop, but also the crop development, environment and management should be considered when assessing transpiration.
Evapotranspiration is a component of the hydrologic cycle. It influences the movement and distribution of water in natural and agricultural systems, affects soil moisture, regulates plant water use, and plays an important role in local and regional climate by transferring both water vapor and heat to the atmosphere. The rate of evapotranspiration depends on factors such as solar radiation, air temperature, humidity, wind speed, soil moisture availability, and the type and condition of vegetation.
In hydrology, agriculture, meteorology, and water-resource engineering, evapotranspiration is commonly used to estimate water loss from land surfaces and crops. Accurate estimation of evapotranspiration is essential for irrigation planning, drought assessment, watershed management, and the sustainable use of water resources.
