Air temp; humidity; wind; plant matter (characteristics as well as exposed faces, as well as health of the plant)
Some of the factors that affect a particular species' transpiration rates include the texture and size of the leaf, as well as the internal abitily of the plant to retain moisture in its fibers. Succulents, for example often have waxy outer texture and fiberous internal chambers that maintain water even through extended drought. A different mechanism that plants display to reduce transpiration is a "hairy" outer texture that is in essence shade-ing the leaf surface from the direct sunlight. Old Man's Beard castus demonstrate this technique.
Tall turf fescue grass, as an example has a large surface area from which to lose water (or transpirate) front and back of entire grass strand. At the same time, it does not have the capacity to store much water in its internal cells. It is one of the "thirstiest" plants commonly seen in American landscapes.
Evapotranspiration is the sum total of land evaporation and plant transpiration. In other words, it is the measure of the movement of water from the Earth's surface to the atmosphere. Evaporation occurs from the soil and bodies of water and transpiration occurs through the stomata (or pores) on plant leaves. It is a part of the natural water cycle on Earth. Some factors which affect it include temperature, relative air humidity, and climate conditions (drier, moving air will increase evapotranspiration versus humid, still air). Also, certain types of plants transpirate more than others depending on their relative amounts of foliage.
We know that evapotranspiration is the combination of evaporation and transpiration.There are several factors which causes evapotranspiration.Some of them are;
- humidity( the amount of water vapor in the air).when humidity increases transpiration decreases.
- air temperature
- the movement of wind and air across an area
- the moisture in plant's soil
- type of plant involved in the transpiration process