Differences between AgERA5 and ERA5-Land

Hi,

here you cancheck the main differences between ERA5 and ERA5-Land:

https://confluence.ecmwf.int/x/fdJ0B

Regarding daily data please have a look at the following link:

https://confluence.ecmwf.int/x/BD6kDQ

Best

Michela

Hi Michela

Thanks! But that link doesn't provide me with information on the differences between AgERA5 and ERA5-Land. Both provide data at high resolution. As a naïve user  which one should I use? Some guidance on this would be helpful, and should probably be included on the main catalogue pages, and not hidden away in the documentation.

Thanks!

Rutger

Hi Rutger,

ERA5-Land is a reanalysis dataset which provides output at 0.1 degree resolution (and is forced by ERA5 atmospheric parameters); AgERA5 uses the ERA5 dataset (0.25 degree resolution) which is interpolated to 0.1 degree resolution.

This page may help:

The family of ERA5 datasets

The user can then decide which dataset is most appropriate for their own particular needs.

Hope that helps,

Kevin

Thanks Kevin!

Again, AgERA5 is not mentioned on the page that you linked. I fear that for many users it will not be clear whether (or when) the interpolated reanalysis would be preferable to the land surface component at similar resolution. I guess we'll need to do some evaluation first!

Thanks in any case

Rutger

Hi Rutger; you are correct, the page I sent lists the original ERA5 family of datasets; as AgERA5 is a dataset based on ERA5 which is produced by a 3rd party so is not included on that page. It would be good to see the results of your evaluation! 

Thanks,

Kevin

Hi Rutger,

I have recently had the similar dilemma when I needed to recommend the dataset to a partner on the project I am working on. They were interested in daily data for the small area in Austria.

Besides of probable differences in accuracy, which I guess the analysis still needs to be done, there are a few technical and practical things to consider:

• The parameters in AgERA5 and ERA5-Land are not the same so this played a big role in which dataset we decided to use
• When downloading ERA5-Land you can download all parameters in one request. However when downloading AgERA5 you can only do one parameter per request. And not all the parameters have all same statistics calculated.
• Even though in AgERA5 daily statistics are calculated that doesn't mean the less data is downloaded, because in this dataset you can't choose the area. The daily data for the whole globe is way bigger than hourly data on a small area. In my case this played a role...
• The limit on number of fields in one request in ERA5-Land is 100.000 and for AgERA5 is 100, so in one case it will be one request in the other most likely bunch of small requests (more loops and more code)

I hope this helps a little...

Regards,
Milana

Hi just to revive this old thread again, but some important differences between AgERA5 and ERA5-land were not mentioned:

• AgERA5 is indeed coarser then ERA5-land. The reason for this is that AgERA5 is based on a statistical bias correction of ERA5, while for ERA5-land a full model reanalysis is carried out. The statistical bias corrections were derived from the differences between the ECMWF HRES model and ERA5. Therefore, if you need to combine a historical weather dataset with a weather forecast you may be better off using AgERA5+HRES instead of ERA5-Land+HRES.
• The variables in AgERA5 were designed with agrometeorological applications in mind which means that the dataset may be less suitable outside this domain.
• The aggregation of hourly to daily values takes into account the local day/night definition across the earth. This is different from the daily aggregated values that are for example available on Google Earth: https://developers.google.com/earth-engine/datasets/catalog/ECMWF_ERA5_LAND_DAILY_RAW

Moreover, I see some comments regarding limitations on data downloads for AgERA5 which are not clear to me. But if you are interested in using AgERA5 you may want to give AgERA5tools a try: https://agera5tools.readthedocs.io AgERA5tools can do the downloading and sub-setting for you and has the capacity to serve time-series of AgERA5 data on an HTTP API.

Finally, it should be realized that the development of AgERA5 was already started when ERA5-land did not exist. Moreover, for a long time ERA5-Land had quite a long delay on real time (was 3 months, now about 5 days) while AgERA5 always had a delay similar to ERA5. Nevertheless, for developing an AgERA5 v2 it would be logical to take ERA5-Land as its base instead of ERA5.