Urban Cooling - Using potential Evapotranspiration Raster instead of ET 0

Hello,
I have a question about the input data required: does InVEST distinguish between reference and potential evapotranspiration (ET0 and ETp)? Or do you know if there are differences between ET0 and ETp, which will change my results?

The user guide explains that a raster representing reference evapotranspiration (ET0) is needed - our meteorological climate centre provides daily, monthly and yearly rasters showing potential evapotranspiration (ETp) over grass, which are calculated with the model AMBAV. This model still uses the Penman-Monteith equation, which, however, has been changed and expanded to reflect national climatic and soil-physical conditions. Therefore, I would like to use those rasters for the modelling.

Futhermore, the kc-calculator requires monthly ETp-values, which confuses me little bit.

Thank you very much!

Claudia

Hi Claudia,

Our model does not distinguish between ET0 and ETp. We use Allen et al. 1998 (http://www.fao.org/3/X0490E/x0490e00.htm#Contents) as a main source of information and that states the following:

The evapotranspiration rate from a reference surface, not short of water, is called the reference crop evapotranspiration or reference evapotranspiration and is denoted as ETo. The reference surface is a hypothetical grass reference crop with specific characteristics. The use of other denominations such as potential ET is strongly discouraged due to ambiguities in their definitions.

From your description the ETp data you have available sounds very similar in method to the ET0 data we suggest in our Users Guide (http://releases.naturalcapitalproject.org/invest-userguide/latest/reservoirhydropowerproduction.html#average-annual-reference-evapotranspiration-et-0). To get an idea of the difference between your ETp dataset and ET0 you could compare data and results with the ET0 global dataset: https://cgiarcsi.community/data/global-aridity-and-pet-database/.

I hope this helps you along.

Best,
Roy

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