Hello all,

I have a question about the unit of monthly total precipitation of ERA5 monthly averaged data on single levels. I saw that the unit of it indicates as 'meter', so it mean that in order to have precipitation in mm/month I should only multiple it to 1000? I ask it because after multiplying to 1000 I saw some high values in the data.

So, I want to ask you if you please tell me after downloading these data (in monthly average, not hourly) is it enough to just multiple them by 1000 to have monthly precipitation data in mm/month?

Thank you all

9 Comments

  1. Michela Giusti

    Hi,

    the accumulations in monthly means have been scaled to have units that include "per day", so the hydrological parameters are in units of "m of water per day". To have data in mm/month:

    total (mm per month) =1000* total precipitation*no. days/month


    Thanks

    1. mohamed abdallah

      Hello,
      Michela Giusti
      Thank you for the interesting information, I am interested in this data and I downloaded it from 1979 to 2021, to convert to mm/month I multiply by 1000*30 is it right?

      1. Michela Giusti

        Hi,

        please have a look at the following link (table 1 row 3 column 8):

        https://confluence.ecmwf.int/x/hrTICw

        Thanks

        1. mohamed abdallah

          Thank you Michela Giusti,

  2. Behzad Navidi

    Dear Michela Giusti
    Thank you,
    But I believe monthly total precipitation values are given as monthly sums.
    And all other parameters are provided as monthly averages.

    I found it after posting my question. Here is the reference: https://developers.google.com/earth-engine/datasets/catalog/ECMWF_ERA5_MONTHLY#description


    1. Michela Giusti

      Dear Behzad Navidi

      the reference above is not a Copernicus product. If you download the data from the Copernicus Climate Data Store the monthly total precipitation values of ERA5 monthly averaged data on single levels from 1979 to present have units that include m of water per day. Please have a look at the following link: ERA5: data documentation#Monthlymeans


      Thanks

      Michela

  3. Behzad Navidi

    Well, is this an official answer from ECMWF staff or not?

    1. Michela Giusti

      Hello Behzad,

      Yes, I work on the C3S Support Desk, where we deal with queries regarding ERA5.

      The dataset you referred to is not an ‘official’ C3S dataset. C3S data are available to all users to reuse (subject to agreement to the relevant licence).

      They (Google) have taken the data and post-processed it to produce a new dataset for the Google Earth Engine. As such, we have no control over how they process and present the data.

      The C3S ERA5 data from Copernicus Climate Data Store are the ‘official’ ERA5 data, and are described in detail in the official ERA5: data documentation. In this document it states that the monthly data are given in units of m (per day) for each month.

      Hope that helps,

      Michela

      1. Behzad Navidi

        You are right. Thank You so Much.

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