Define evapotranspiration and potential evapotranspiration.

• A. ET is evaporation only; PET is precipitation
• B. ET is evaporation from soil only; PET is potential rainfall
• C. ET is actual evaporation plus plant transpiration; PET is the amount of ET that would occur if water availability were unlimited
• D. ET is plant transpiration only; PET equals rainfall

Answer: (C)

ET represents how water is lost to the atmosphere from a landscape, and it includes both evaporation from surfaces (soil, water) and transpiration from plant leaves. The amount of ET that would occur if water were not limiting is called potential evapotranspiration, which depends on climate factors like temperature, solar radiation, humidity, and wind. So the correct understanding is that ET is actual evaporation plus plant transpiration, while PET is the hypothetical maximum ET under unlimited water supply. This distinguishes ET from rainfall and from evaporation alone, since plants add transpiration and water availability sets how much ET can actually happen. In practice, ET may be lower than PET when soils are dry, and PET reflects atmospheric demand rather than actual water loss.