Potential Evaporation on ERA5 and ERA5L


I'm working on ERA5 and ERA5L reanalysis and particularly on evaporation.

I'm trying to compare the values themselves and to compare them to Potential ET for agriculture (Penman-Monteith) via spatialized "observations" (METEO-FRANCE network).

About Potential Evaporation (PEV - var251), I cumulated PEV on 2018 (00h values for ERA5L and each hour values for ERA5) and there's a big difference over France (annual mean around 800mm for ERA5 and 1700mm for ERA5L).

There are also surprising 0mm values on the center of France on ERA5 and not on ERA5L.

What's wrong with my approach?

What's the formula used to calculate PEV for ERA5 and ERA5L ?

Is it really comparable with PET ?

Is it better to use Evapotranspiration (parameter 182) ?

Best regards.


Hi Franck,

I was just wondering if you found the answer to your questions? I have similar questions too.



HI Mohamad ! Noone answered me. We decided (Meteo-France) to calculate PET with meteorogical parameters and FAO-56 penman monteith formula (or a Meteo penman monteith formula). It's much better. F.


I am going to a similar process - now I will try to calculate ET0 from radiation and temperature according to Makkink (1957) that uses the Penman formula.

May I ask which meteorological parameters you used from ERA5-Land for this calculation?


Makkink G.F. 1957. Testing the Penman formula by means of lysimeters. J. Intern. Water Engineering, 11: 277-288.

Hi Mohamad Nobakht,

Did you found any answer for your question?

I have a similar one.

Best regards

The definitions of potential and reference evapotranspiration may vary according to the scientific application and can have the same definition in some cases. Users should therefore ensure that the definition of this parameter is suitable for their application.

Please note that to give more flexibility to users,  PEV in ERA5 and ERA5Land are not computed in the same way:

  • ERA5: the definition of PEV in ERA5 is computed for agricultural land as if it is well watered (no soil moisture stress)  and assuming that the atmosphere is not affected by this artificial surface condition. 
  • ERA5Land: the definition of PEV in ERA5Land is computed as an open water evaporation (Pan evaporation) and assuming that the atmosphere is not affected by this artificial surface condition.