Why are evaporation and transpiration often grouped together as evapotranspiration?

In hydrologic and climatic studies, the term evapotranspiration is used to describe the combined loss of water from the Earth's surface to the atmosphere through two distinct but related processes: evaporation and transpiration.12

These processes are grouped together because both represent the return of water to the atmosphere from the land surface, and they are often difficult to distinguish or measure separately in a natural environment. Specifically:2

• Evaporation involves the transition of liquid water from soil surfaces or open water bodies into water vapour.12
• Transpiration involves the process by which plants draw moisture from the soil through their roots and discharge it as water vapour through their leaves.23

Because both processes are driven by similar environmental factors—such as solar radiation, temperature, wind, and atmospheric humidity—they are collectively analyzed to determine the total water loss from a landscape, which is essential for managing irrigation and understanding the water cycle.142