Excess heat factor

[chpolste]

Description

doi:10.3390/ijerph120100227

Considered implementing this as part of thermofeel at first, but the requirement for time-series operations complicates a pure numpy implementation and strongly favours a higher-level implementation based on xarray as proposed here, using earthkit-transforms for the temporal aggregations.

TODO

• Heatwave severity index
• Cold factor implementation
• Support day-of-year climatology in significance index for warm/cold spell applications
• Example notebook, incl. local time features
• Unit handling in metadata (wait for metadata decorator support)
• Compatibility with other timedelta types (wait for earthkit time support)
• API documentation
• Unit tests

Contributor Declaration

By opening this pull request, I affirm the following:

• All authors agree to the Contributor License Agreement.
• The code follows the project's coding standards.
• I have performed self-review and added comments where needed.
• I have added or updated tests to verify that my changes are effective and functional.
• I have run all existing tests and confirmed they pass.