Set correct calendar when reading file dates (#2826)

(cherry picked from commit e2fad72)

Author: bouweandela

esmvalcore/local.py

@@ -161,8 +161,16 @@ def _get_start_end_date(
         with Dataset(file) as dataset:
             for variable in dataset.variables.values():
                 var_name = _get_var_name(variable)
-                if var_name == "time" and "units" in variable.ncattrs():
-                    time_units = Unit(variable.getncattr("units"))
+                attrs = variable.ncattrs()
+                if (
+                    var_name == "time"
+                    and "units" in attrs
+                    and "calendar" in attrs
+                ):
+                    time_units = Unit(
+                        variable.getncattr("units"),
+                        calendar=variable.getncattr("calendar"),
+                    )
                     start_date = isodate.date_isoformat(
                         time_units.num2date(variable[0]),
                         format=isodate.isostrf.DATE_BAS_COMPLETE,

tests/unit/local/test_time.py

@@ -5,6 +5,7 @@
 import iris
 import pyesgf
 import pytest
+from cf_units import Unit
 
 from esmvalcore.esgf import ESGFFile
 from esmvalcore.local import (
@@ -182,11 +183,11 @@ def test_read_datetime_from_cube(tmp_path):
     temp_file = tmp_path / "test.nc"
     cube = iris.cube.Cube([0, 0, 0, 0], var_name="var")
     time = iris.coords.DimCoord(
-        [0, 100, 200, 366],
+        [0, 100, 200, 361],
         standard_name=None,
         long_name="time",
         var_name="t",
-        units="days since 1990-01-01",
+        units=Unit("days since 1990-01-01", calendar="360_day"),
     )
     cube.add_dim_coord(time, 0)
     iris.save(cube, temp_file)