Lazy derivation of vegfrac

esmvalcore/preprocessor/_derive/vegfrac.py

@@ -1,10 +1,10 @@
 """Derivation of variable `vegFrac`."""
 
 import dask.array as da
-import iris
 from iris import NameConstraint
 
 from .._regrid import regrid
+from .._shared import broadcast_to_shape
 from ._baseclass import DerivedVariableBase
 
 
@@ -15,9 +15,16 @@
     def required(project):
         """Declare the variables needed for derivation."""
         required = [
-            {"short_name": "baresoilFrac"},
-            {"short_name": "residualFrac"},
-            {"short_name": "sftlf", "mip": "fx"},
+            {
+                "short_name": "baresoilFrac",
+            },
+            {
+                "short_name": "residualFrac",
+            },
+            {
+                "short_name": "sftlf",
+                "mip": "fx",
+            },
         ]
         return required
 
@@ -34,11 +41,21 @@
 
         # Add time dimension to sftlf
         target_shape_sftlf = (baresoilfrac_cube.shape[0], *sftlf_cube.shape)
-        sftlf_data = iris.util.broadcast_to_shape(
-            sftlf_cube.data, target_shape_sftlf, (1, 2)
+        target_chunks_sftlf = (
+            tuple(
+                baresoilfrac_cube.lazy_data().chunks[0],
+                *sftlf_cube.lazy_data().chunks,
+            )
+            if baresoilfrac_cube.has_lazy_data()
+            else None
+        )
+        sftlf_data = broadcast_to_shape(
+            sftlf_cube.core_data(),
+            target_shape_sftlf,
+            dim_map=(1, 2),
+            chunks=target_chunks_sftlf,
         )
         sftlf_cube = baresoilfrac_cube.copy(sftlf_data)
-        sftlf_cube.data = sftlf_cube.lazy_data()
 
         # Regrid sftlf if necessary and adapt mask
         if sftlf_cube.shape != baresoilfrac_cube.shape: