Reference evapotranspiration


My colleague and I are new to InVEST. We are currently setting up the parameters and data for the InVEST Annual Water Yield model. May we ask if anyone knows if we can use the Priestley-Taylor PET method (as it is) for Reference evapotranspiration in InVEST modelling? Or is there some form of conversion required?

Thank you.

With best wishes,


Hi @ry_es_nz -

I’ve never used the Priestley-Taylor method, and taking a quick look at it, it seems fine to use, but it’s unclear to me what the output units are. The Annual Water Yield model requires an average annual value in millimeters, and I’m seeing people report values from the Priestley-Taylor method in depth units, but it seems necessary to do some research as to whether they had to apply any conversion factors. Perhaps someone else has more experience with this equation?

~ Stacie

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Hi Stacie,
Thank you for your help. The PET layer was developed by NIWA (National Institute of Water and Atmospheric Research), an NZ government research institution. The PET layer is expressed in millimetres, so we will probably run with this at the moment. However, we will also do some research and will consider any other suggestions from this discussion list.