Evapotranspiration (ET) is an important part of the hydrological cycle. Evaporation is the movement (vaporization) of water to the air from the soil, water bodies and canopy interception. Transpiration is the loss of water as vapour through stomata in the plant leaves. Together, evaporation and transpiration are known as evapotranspiration. ET is an indicator of how much water vegetation needs for healthy growth and productivity. The energy that is required for ET is provided by the sun. ET indicates the daily loss of moisture from the soil, and thus the necessary complement to maintain the necessary moisture level in the soil. ET is expressed in millimeters per week.
ETdef indicates the difference between potential ET (how much water can evaporate if there is sufficient water available) and actual ET (water that is actually evaporating). ETdef is thus the amount by which the available moisture fails to meet the demand for water, and it indicates whether irrigation is needed or not. ETdef is a direct damage parameter and an indicator of missed yield. ETdef is expressed in millimeters per week.
BM indicates the dry matter production of tubers, roots, stems, flowers, needles, cereals and fruit over time. It indicates the growth of a plant over a week. The BM is expressed in kilogram per hectare per week.
P shows the distribution of rainfall over the area. P is expressed in millimeters per week.
P-ET indicates the difference between rainfall and actual ET. It is an indication of the wetness of the soil. P-ET is expressed in millimeters per week.