@TomNicholas I forgot about this sorry.

No worries!

I just made a quick check with the latest xarray master and I still have the problem ... see code.

3498 added a new keyword argument to open_mfdataset, to choose which file to load to attributes from, can you try using that?

time.encoding is empty while it is as expected when opening any of the files with open_dataset instead

If this is the case, then to solve your original problem, you could also try using the preprocess argument to open_mfdataset to store the encoding somewhere where it won't be lost? i.e.

```python def store_encoding(ds): encoding = ds['time'].encoding ds.time.attrs['calendar_encoding'] = encoding return ds

snw = xr.open_mfdataset(l_f, combine='nested', concat_dim='time', master_file=lf[0], preprocess=store_encoding)['snw'] ```

Related question but maybe out of line, is there any way to know that the snw.time type is cftime.DatetimeNoLeap (as it is visible in the overview of snw.time)?

I'm not familiar with these classes, but presumably you mean more than just checking with isinstance()? e.g. python from cftime import DatetimeNoLeap print(isinstance(snw.time.values, cftime.DatetimeNoLeap))

@sbiner I know it's been a while, but I expect that #3498 and #3877 probably resolve your issue?

If open_mfdataset() is actually dropping the encoding, then this is an issue related to #1614. That's because in open_mfdataset() while the attrs are explicitly set to those of the first supplied dataset, I don't see any similar explicit treatment of the encoding. I think that means the encoding is being set by what happens inside the core of auto_combine(), and is presumably being lost upon some of the concat or merge operations which happen inside auto_combine().

So I think to fix this then either open_mfdataset() should contain explicit treatment of the encoding, or the rules for propagating the encoding through the auto_combine() should be solidified.