better calendar options and doc

Co-authored-by: Pascal Bourgault <[email protected]>

CHANGELOG.rst

@@ -29,7 +29,7 @@ New features and enhancements
 * ``xclim.indices.run_length.runs_with_holes`` allows to input a condition that must be met for a run to start and a second condition that must be met for the run to stop. (:pull:`1778`).
 * New generic compute function ``xclim.indices.generic.thresholded_events`` that finds events based on a threshold condition and returns basic stats for each. See also ``xclim.indices.run_length.find_events``. (:pull:`1778`).
 * ``xclim.core.units.rate2amount`` and ``xclim.core.units.amount2rate`` can now also accept quantities (pint objects or strings), in which case the ``dim`` argument must be the ``time`` coordinate through which we can find the sampling rate. (:pull:`1778`).
-* ``xclim.indices.stats.standardized_index`` now supports a weekly resampling frequency. Only "standard" calendar is supported for this mode. (:issue:`1892`, :pull:`1952`)
+* ``xclim.indices.stats.standardized_index`` now supports a weekly resampling frequency. Only "standard" calendars using numpy's `datetime64` dtype are supported for this mode. (:issue:`1892`, :pull:`1952`)
 
 Bug fixes
 ^^^^^^^^^

tests/test_indices.py

@@ -672,7 +672,7 @@ def test_standardized_precipitation_index(
             ds = ds.convert_calendar("366_day", missing=np.nan)
         elif freq == "W":
             # only standard calendar supported with freq="W"
-            ds = ds.convert_calendar("standard", missing=np.nan, align_on="year")
+            ds = ds.convert_calendar("standard", missing=np.nan, align_on="year", use_cftime=False)
         pr = ds.pr.sel(time=slice("1998", "2000"))
         pr_cal = ds.pr.sel(time=slice("1950", "1980"))
         fitkwargs = {}

xclim/indices/_agro.py

@@ -1163,7 +1163,7 @@ def standardized_precipitation_index(
     * Supported statistical distributions are: ["gamma", "fisk"], where "fisk" is scipy's implementation of
        a log-logistic distribution
     * Supported frequencies are daily ("D"), weekly ("W"), and monthly ("MS").
-      Weekly frequency will only work if the input array has a "standard" calendar.
+      Weekly frequency will only work if the input array has a "standard" (non-cftime) calendar.
     * If `params` is given as input, it overrides the `cal_start`, `cal_end`, `freq` and `window`, `dist` and `method` options.
     * "APP" method only supports two-parameter distributions. Parameter `loc` needs to be fixed to use method `APP`.
     * The standardized index is bounded by ±8.21. 8.21 is the largest standardized index as constrained by the float64 precision in