Use ResamplingIndicatorWithIndexing for chill_units

tests/test_atmos.py

@@ -6,6 +6,7 @@
 import xarray as xr
 
 from xclim import atmos, set_options
+from xclim.indices.helpers import make_hourly_temperature
 
 K2C = 273.16
 
@@ -624,3 +625,16 @@ def test_late_frost_days(self, atmosds):
         lfd = atmos.late_frost_days(tasmin, date_bounds=("04-01", "06-30"))
 
         np.testing.assert_allclose(lfd.isel(time=0), exp, rtol=1e-03)
+
+
+def test_chill_units(atmosds):
+    tasmax = atmosds.tasmax
+    tasmin = atmosds.tasmin
+    tas = make_hourly_temperature(tasmin, tasmax)
+    cu = atmos.chill_units(tas, date_bounds=("04-01", "06-30"))
+    assert cu.attrs["units"] == "1"
+    assert cu.name == "cu"
+    assert cu.time.size == 4
+
+    exp = [-5029.5, -6634.5, -5993.0, -6596.0, -5654.0]
+    np.testing.assert_allclose(cu.isel(time=0), exp, rtol=1e-03)

xclim/indicators/atmos/_temperature.py

@@ -116,6 +116,13 @@ class TempWithIndexing(ResamplingIndicatorWithIndexing):
     keywords = "temperature"
 
 
+class TempHourlyWithIndexing(ResamplingIndicatorWithIndexing):
+    """Indicators involving hourly temperature and adding an indexing possibility."""
+
+    src_freq = "h"
+    keywords = "temperature"
+
+
 tn_days_above = TempWithIndexing(
     title="Number of days with minimum temperature above a given threshold",
     identifier="tn_days_above",
@@ -1459,8 +1466,7 @@ def cfcheck(self, tas, snd=None):
     title="Chill portions",
     identifier="cp",
     units="",
-    # TODO: check what this does
-    cell_methods="",
+    cell_methods="time: sum",
     description="Chill portions are a measure to estimate the bud breaking potential of different crops. "
     "The constants and functions are taken from Luedeling et al. (2009) which formalises "
     "the method described in Fishman et al. (1987). ",
@@ -1478,14 +1484,15 @@ def cfcheck(self, tas, snd=None):
     compute=indices.chill_portions,
 )
 
-chill_units = TempHourly(
+chill_units = TempHourlyWithIndexing(
     title="Chill units",
     identifier="cu",
     units="",
+    cell_methods="time: sum",
     description="Chill units are a measure to estimate the bud breaking potential of different crops based on the Utah model developed in "
     "Richardson et al. (1974). The Utah model assigns a weight to each hour depending on the temperature recognising that high temperatures can "
     "actually decrease the potential for bud breaking.",
     long_name="Chill units after the Utah Model",
-    allowed_periods=["A"],
+    allowed_periods=["Y"],
     compute=indices.chill_units,
 )

xclim/indices/_agro.py

@@ -1570,6 +1570,7 @@ def _apply_chill_portion_one_season(tas_K):
         tas_K,
         input_core_dims=[["time"]],
         output_core_dims=[["time"]],
+        output_dtypes=[tas_K.dtype],
         dask="parallelized",
     ).sum("time")