Fix ERA5 native6 fix to handle single monthly-averaged NetCDF files.

esmvalcore/cmor/_fixes/native6/era5.py

@@ -23,18 +23,21 @@ def get_frequency(cube):
         return "fx"
 
     time.convert_units("days since 1850-1-1 00:00:00.0")
-    if len(time.points) == 1:
-        if cube.long_name != "Geopotential":
-            raise ValueError(
-                "Unable to infer frequency of cube "
-                f"with length 1 time dimension: {cube}"
-            )
-        return "fx"
 
-    interval = time.points[1] - time.points[0]
-    if interval - 1 / 24 < 1e-4:
-        return "hourly"
+    if len(time.points) == 1 and cube.long_name == "Geopotential":
+        return "fx"
 
+    if len(time.points) > 1:
+        interval = time.points[1] - time.points[0]
+        if interval - 1 / 24 < 1e-4:
+            return "hourly"
+    else:
+        logger.warning(
+            "Unable to infer frequency of cube "
+            "with length 1 time dimension: %s,"
+            "assuming 'monthly' frequency",
+            str(cube),
+        )
     return "monthly"
 
 

tests/integration/cmor/_fixes/native6/test_era5.py

@@ -89,8 +89,7 @@ def test_get_frequency_fx():
     )
     assert get_frequency(cube) == "fx"
     cube.long_name = "Not geopotential"
-    with pytest.raises(ValueError):
-        get_frequency(cube)
+    assert get_frequency(cube) == "monthly"
 
 
 def _era5_latitude():