Potential Evapotranspiration 

Definition of Potential Evapotranspiration

Potential evapotranspiration is defined as the amount of evaporation that would occur if a sufficient water source were available. If the actual evapotranspiration is considered the net result of atmospheric demand for moisture from a surface and the ability of the surface to supply moisture, then PET is a measure of the demand side. Surface and air temperatures, insolation, and wind all affect this. A dryland is a place where annual potential evaporation exceeds annual precipitation.

 Potential evapotranspiration is higher in the summer, on less cloudy days, and closer to the equator, because of the higher levels of solar radiation that provides the energy for evaporation. Potential evapotranspiration is also higher on windy days because the evaporated moisture can be quickly moved from the ground or plant surface, allowing more evaporation to fill its place. Potential evapotranspiration is expressed in terms of a depth of water, and can be graphed during the year. PET is usually measured indirectly, from other climatic factors, but also depends on the surface type, such as free water (for lakes and oceans), the soil type for bare soil, and the vegetation. 


PET (average)

PET (change)

PET (anomalies)

Represented range 

PET (average): 0 mm/year - 2,700 mm/year

PET (change): -3.17 mm/year - 2.77 mm/year

PET (anomalies): -25.87 mm/year - 22.12 mm/year


The algorithm used for the MOD16 data product collection is based on the logic of the Penman-Monteith equation, which includes inputs of daily meteorological reanalysis data along with MODIS remotely sensed data products such as vegetation property dynamics, albedo, and land cover.


MOD16A2 v006 - MODIS/Terra Net Evapotranspiration 8-Day L4 Global 500 m SIN Grid 

National Aeronautics and Space Administration (NASA) – MODIS


MOD16A2 v006 - MODIS/Terra Net Evapotranspiration 8-Day L4 Global 500 m SIN Grid 


The Potential Evapotranspiration product comes from MOD16A2 MODIS/Terra Net Evapotranspiration 8-Day L4 Global 500m version 6 image collection to generate a time series for the period 2000 to 2017.

Spatial resolution 

Pixel size: 500 m

Temporal resolution 

Global time series available from 2000 to present.

 High temporal resolution: Daily revisit time, graph shows less-cloudy image during 16/8 days