When does maximum evapotranspiration (ET) generally occur?

Maximum evapotranspiration (ET) generally occurs when atmospheric demand peaks. This is typically during the warmest part of the day when temperatures are highest, and solar radiation is at its peak, leading to an increase in moisture loss from both soil and plant surfaces.

During these times, factors such as higher temperatures, increased wind speed, and greater sunlight work together to enhance the process of evapotranspiration. As a result, plants transpire more as they attempt to cool themselves, while evaporation from the soil also increases due to the higher temperatures and energy available.

The other options do not align with the conditions that promote maximum ET. Heavy rainfall, for example, often reduces ET since the soil becomes saturated and water is not lost through evaporation as readily. In the early morning and at night, lower temperatures and reduced solar radiation lead to lower atmospheric demand, consequently resulting in reduced rates of evapotranspiration compared to peak afternoon hours when demand is highest.