to_xarray from GRIB dropping units

[JamesVarndell]

What happened?

When calling to_xarray() on GRIBReader objects in earthkit-data, somnetimes the data units are lost. This seems to happen when there is a single variable in the GRIB input - but when there are multiple variables, the units are correctly carried into the xarray object.

What are the steps to reproduce the bug?

import earthkit.data

data = earthkit.data.from_source(
    'cds',
    'reanalysis-era5-single-levels',
    {
        'product_type': 'reanalysis',
        'variable': '2m_temperature',
        'year': '2024',
        'month': '08',
        'day': '09',
        'time': '18:00',
    },
)

ds = data.to_xarray()

If you look at the global and variable attributes of ds, there are no units in either. However, if we slightly tweak the above request to as for two variables as below, then the two variables in ds both have their correct units in the variable attributes.

import earthkit.data

data = earthkit.data.from_source(
    'cds',
    'reanalysis-era5-single-levels',
    {
        'product_type': 'reanalysis',
        'variable': ['2m_temperature', 'total_precipitation'],
        'year': '2024',
        'month': '08',
        'day': '09',
        'time': '18:00',
    },
)

ds = data.to_xarray()

Version

0.11.4

Platform (OS and architecture)

MacOS

Relevant log output

No response

Accompanying data

No response

Organisation

ECMWF