Water Use By Turf -pET Calculator
The use of water by plants can be estimated by
calculating what is known as potential evapotranspiration (pET). This is the possible loss
of water (or use) through evaporation and transpiration. Transpiration is the movement of water
through a plant from the soil into the roots, up the stem, and out through the leaves.
Simple calculations of pET can be based on sun, wind, temperature, and humidity.
True water use varies depending upon many other factors. When calculated
daily, the accuracy of estimates will change from day to day. However, these will usually
average out over a week to ten days, and the sum over that period may be quite accurate.
Persons using pET to estimate water use and schedule irrigation also must adjust pET
values based on their experience with their own specific conditions, especially including
Sky Conditions (sunlight):
The value of daily solar radiation is dependent on day length, angle of the
sun from the horizon throughout the day, and the amount of clouds the sunlight must
penetrate. To estimate sunlight, select cloud cover and time of year. The calculator
will automatically calculate the solar radiation value.
Average Wind Speed:
The effect of wind on pET reaches a maximum under moderately breezy
Once again, this is the average wind speed. We
often think of the gustier winds as being average because they are
most noticeable, but they are not average. Also this is a daily
average, wind conditions vary through the day.