Add percentage difference to xscen.aggregate.compute_deltas

[mccrayc]

Addressing a Problem?

When we calculate relative changes for climate change, we are often presenting deltas in terms of % change relative to the past climate. Currently, compute_deltas allows for absolute or relative deltas, but relative is a simple ratio future/past (in the case of a future and past climate delta). I believe it would be useful to add a percentage change option to "kind."

Potential Solution

In xscen.aggregate, add a new option for parameter 'kind': '%' associated with _kind = 'percentage' or 'percent'. Something like:

with xr.set_options(keep_attrs=True):
    if _kind == "absolute":
        deltas[v_name] = other_hz[vv] - ref[vv]
    elif _kind == "relative":
        deltas[v_name] = other_hz[vv] / ref[vv]
        deltas[v_name].attrs["units"] = ""
    elif _kind == "percentage":
        deltas[v_name] = (other_hz[vv] - ref[vv]) / ref[vv] * 100
        deltas[v_name].attrs["units"] = "%"

This will lead to NaNs in cases where the reference value is 0 (for example, for certain precipitation variables like prsn). I don't think this should be too much of an issue though, as this is handled well by xarray.

Additional context

The *100 to convert the decimal change to % may not be desired or could be an option.

Contribution

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