Evaporation is water becoming vapour from any surface — a puddle, a lake, wet clothing. Transpiration is the same physical change but specifically water moving through a plant and released as vapour through its leaves. Transpiration is a biological process; evaporation is a purely physical one.
The core difference
The same change of state, distinguished by whether a plant is involved.
- evaporation — liquid water to vapour from any surface.
- transpiration — water drawn up through a plant and released through the stomata in its leaves.
- evapotranspiration — the combined total, which is what hydrologists actually measure.
Why transpiration matters
It is not a side effect. Transpiration is what pulls water up from the roots — evaporation at the leaves creates the tension that drags the whole column upward, which is how water reaches the top of a tall tree without a pump. It also cools the plant.
The combined term
In practice the two are difficult to separate in the field, which is why evapotranspiration exists as a single measured quantity in hydrology and agriculture.
