Please add option for 'weekly' frequency in the SPI family of models

[C15H24]

Addressing a Problem?

No response

Potential Solution

the function standardized_precipitation_index accepts freq = 'W' as signifying the nature of the groupings is weekly - and any downstream adjustments that would need to be made to validate the output

Additional context

Many projects in government are beginning to operate and produce products on a weekly basis

Contribution

• I would be willing/able to open a Pull Request to contribute this feature.

Code of Conduct

• I agree to follow this project's Code of Conduct

[coxipi]

Hi! We can add this indeed. Just a couple caveats:

1. It will only work with standard calendars, as .resample(time="W") and .groupby("time.week") is not yet compatible with cf-time (how to group `cftime` coordinate by `week`? pydata/xarray#6375)
2. Since there is not an integer number of weeks in a year, using .resample(time="W").mean() the days included in week1 can vary from year to year, e.g.

# days included in week 1 between 2000 and 2002
2000: [Jan 3, Jan 9]
2001: [Jan 1, Jan 7]
2002: [Dec31 2001, Jan 6]
...

sometimes Jan 1rst is not included, sometimes Week1 includes days from december, etc. I'm curious to know if this is what you envision when you consider weekly groupings.

[C15H24]

Yes, I envision strict adherence to ISO-8601 weeks :)
So, looks like it would need to be implemented upstream (cftime.datetime) first?

Thank you for your response