Ouranosinc / xclim / 11387045798

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Build Type

push

github

Committed by web-flow

Commit Message

Support for temperature differences in CF attributes (#1836)

Set ``units_metadata`` attribute to ``"temperature: difference"`` for
arrays representing a difference between two temperatures.

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### Pull Request Checklist:
- [x] This PR addresses an already opened issue (for bug fixes /
features)
    - This PR fixes #1822
- [x] Tests for the changes have been added (for bug fixes / features)
- [x] (If applicable) Documentation has been added / updated (for bug
fixes / features)
- [x] CHANGELOG.rst has been updated (with summary of main changes)
- [x] Link to issue (:issue:`number`) and pull request (:pull:`number`)
has been added

### What kind of change does this PR introduce?

* Add ``units_metadata`` attribute set to ``"temperature: difference"``
whenever values represent a difference between two temperatures (degree
days, diurnal amplitude, bias, etc).
* Adjust the units handling functions to recognize this attribute. 
* Modify indices that set units to `delta_degC`, which is not CF
compliant, by the original input DataArray units and the
``units_metadata`` attribute.
* Create new function ``pint2cfattrs`` to convert delta units into a
dictionary of attributes, including ``units_metadata``.


### Does this PR introduce a breaking change?

Yes, units returned by some indices will change.

### Other information:

Run Details

67 of 68 new or added lines in 6 files covered. (98.53%)

12 existing lines in 1 file now uncovered.

9361 of 10476 relevant lines covered (89.36%)

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