diff --git a/src/itzi_core/providers/memory_output.py b/src/itzi_core/providers/memory_output.py
index c29db03..243f85b 100644
--- a/src/itzi_core/providers/memory_output.py
+++ b/src/itzi_core/providers/memory_output.py
@@ -25,20 +25,17 @@
 class MemoryRasterOutputProvider(RasterOutputProvider):
     """Save rasters in memory as numpy arrays."""
 
-    def __init__(self, out_map_names: Mapping[str, str]) -> None:
-        """Initialize output provider with simulation configuration."""
-        # user-selected map names.
-        self.out_map_names = out_map_names
-        self.output_maps_dict: dict[str, list[tuple[datetime | timedelta, np.ndarray]]] = {
-            key: [] for key in self.out_map_names
-        }
+    def __init__(self) -> None:
+        self.output_maps_dict: dict[str, list[tuple[datetime | timedelta, np.ndarray]]] = {}
 
     def write_arrays(
         self, array_dict: Mapping[str, np.ndarray], sim_time: datetime | timedelta
     ) -> None:
         for arr_key, arr in array_dict.items():
             if isinstance(arr, np.ndarray):
-                self.output_maps_dict[arr_key].append((deepcopy(sim_time), arr.copy()))
+                self.output_maps_dict.setdefault(arr_key, []).append(
+                    (deepcopy(sim_time), arr.copy())
+                )
 
 
 class MemoryVectorOutputProvider(VectorOutputProvider):
diff --git a/tests/ea8b/conftest.py b/tests/ea8b/conftest.py
index 022f7ee..8fee5be 100644
--- a/tests/ea8b/conftest.py
+++ b/tests/ea8b/conftest.py
@@ -173,7 +173,7 @@ def ea8b_simulation(ea8b_data, test_data_path, ea8b_temp_path):
             simulation_end_time=sim_config.end_time,
         )
     )
-    raster_output_provider = MemoryRasterOutputProvider(sim_config.output_map_names)
+    raster_output_provider = MemoryRasterOutputProvider()
     vector_output_provider = MemoryVectorOutputProvider()
 
     simulation = (
diff --git a/tests/ea8b/helpers.py b/tests/ea8b/helpers.py
index 2e90887..71c01e8 100644
--- a/tests/ea8b/helpers.py
+++ b/tests/ea8b/helpers.py
@@ -96,7 +96,7 @@ def build_resumed_simulation(
             simulation_end_time=sim_config.end_time,
         )
     )
-    raster_output_provider = MemoryRasterOutputProvider(sim_config.output_map_names)
+    raster_output_provider = MemoryRasterOutputProvider()
     vector_output_provider = MemoryVectorOutputProvider()
 
     simulation = (
diff --git a/tests/test_5by5.py b/tests/test_5by5.py
index ef7a99f..28163e5 100644
--- a/tests/test_5by5.py
+++ b/tests/test_5by5.py
@@ -58,7 +58,7 @@ def _build_diagnostic_simulation(
         surface_flow_parameters=SurfaceFlowParameters(hmin=0.0001, dtmax=dtmax, cfl=0.2),
         infiltration_model=InfiltrationModelType.NULL,
     )
-    raster_output = MemoryRasterOutputProvider(sim_config.output_map_names)
+    raster_output = MemoryRasterOutputProvider()
     simulation = (
         SimulationBuilder(sim_config, domain_5by5.arr_mask, np.float32)
         .with_domain_data(domain_5by5.domain_data)
@@ -161,7 +161,7 @@ def _run_center_pulse_simulation(
         infiltration_model=InfiltrationModelType.NULL,
     )
 
-    raster_output = MemoryRasterOutputProvider(sim_config.output_map_names)
+    raster_output = MemoryRasterOutputProvider()
     simulation = (
         SimulationBuilder(sim_config, domain_5by5.arr_mask, np.float32)
         .with_domain_data(domain_data)
@@ -322,7 +322,7 @@ def sim_5by5(domain_5by5, helpers) -> Simulation:
     )
 
     # Create output provider
-    raster_output = MemoryRasterOutputProvider(sim_config.output_map_names)
+    raster_output = MemoryRasterOutputProvider()
 
     # Build simulation
     simulation = (
diff --git a/tests/test_analytic.py b/tests/test_analytic.py
index 0e88394..173a989 100644
--- a/tests/test_analytic.py
+++ b/tests/test_analytic.py
@@ -155,7 +155,7 @@ def mcdo_norain_sim(test_data_path, test_data_temp_path):
         ),
         surface_flow_parameters=SurfaceFlowParameters(dtmax=2, cfl=0.5),
     )
-    raster_output = MemoryRasterOutputProvider(config.output_map_names)
+    raster_output = MemoryRasterOutputProvider()
     simulation = (
         SimulationBuilder(config, array_mask, np.float32)
         .with_domain_data(domain_data)
@@ -285,7 +285,7 @@ def mcdo_rain_sim(test_data_path, test_data_temp_path):
         surface_flow_parameters=SurfaceFlowParameters(dtmax=2, cfl=0.5),
         dtinf=1,
     )
-    raster_output = MemoryRasterOutputProvider(config.output_map_names)
+    raster_output = MemoryRasterOutputProvider()
     simulation = (
         SimulationBuilder(config, array_mask, np.float32)
         .with_domain_data(domain_data)
diff --git a/tests/test_boundaries.py b/tests/test_boundaries.py
index 439f8a4..3944905 100644
--- a/tests/test_boundaries.py
+++ b/tests/test_boundaries.py
@@ -57,7 +57,7 @@ def sim_5by5_open_boundaries(domain_5by5, helpers):
     )
 
     # Create output provider
-    raster_output = MemoryRasterOutputProvider(sim_config.output_map_names)
+    raster_output = MemoryRasterOutputProvider()
 
     # Build simulation
     simulation = (
diff --git a/tests/test_ea8a.py b/tests/test_ea8a.py
index 2a51d80..849de85 100644
--- a/tests/test_ea8a.py
+++ b/tests/test_ea8a.py
@@ -314,7 +314,7 @@ def ea_test8a_sim(ea_test8a_xarray_data, test_data_path, test_data_temp_path):
     )
 
     # Create output providers
-    raster_output = MemoryRasterOutputProvider(sim_config.output_map_names)
+    raster_output = MemoryRasterOutputProvider()
     vector_output = MemoryVectorOutputProvider()
 
     # Create simulation domain data from input provider
diff --git a/tests/test_hotstart_integration.py b/tests/test_hotstart_integration.py
index afdd560..94aae6a 100644
--- a/tests/test_hotstart_integration.py
+++ b/tests/test_hotstart_integration.py
@@ -94,9 +94,7 @@ def build_simulation(
         domain_5by5: Domain fixture
         hotstart_bytes: Optional hotstart archive bytes
     """
-    raster_output = raster_output_provider or MemoryRasterOutputProvider(
-        sim_config.output_map_names
-    )
+    raster_output = raster_output_provider or MemoryRasterOutputProvider()
 
     builder = (
         SimulationBuilder(sim_config, domain_5by5.arr_mask, np.float32)
@@ -384,7 +382,7 @@ def test_resume_allows_output_provider_change(
     sim_config = baseline_hotstart_run["sim_config"]
     hotstart_bytes = baseline_hotstart_run["checkpoints"]["split_30"]["hotstart_bytes"]
 
-    resumed_output = MemoryRasterOutputProvider(sim_config.output_map_names)
+    resumed_output = MemoryRasterOutputProvider()
     sim_b = build_simulation(
         sim_config,
         domain_5by5,
@@ -414,7 +412,7 @@ def test_resume_allows_output_map_name_change(
         ["water_depth", "max_water_depth", "flow_rate_x", "flow_rate_y", "created_volume"],
     )
     sim_b_config = sim_a_config.model_copy(update={"output_map_names": resumed_output_map_names})
-    resumed_output = MemoryRasterOutputProvider(resumed_output_map_names)
+    resumed_output = MemoryRasterOutputProvider()
     sim_b = build_simulation(
         sim_b_config,
         domain_5by5,
@@ -425,7 +423,6 @@ def test_resume_allows_output_map_name_change(
     run_simulation_to_end(sim_b, skip_initialize=True)
 
     assert sim_b.report.out_map_names == resumed_output_map_names
-    assert resumed_output.out_map_names == resumed_output_map_names
     assert resumed_output.output_maps_dict["water_depth"]
     assert resumed_output.output_maps_dict["max_water_depth"]
     np.testing.assert_allclose(
@@ -466,7 +463,7 @@ def test_resume_applies_new_record_step_cadence(
 
     resumed_record_step = timedelta(seconds=10)
     resumed_config = original_config.model_copy(update={"record_step": resumed_record_step})
-    resumed_output = MemoryRasterOutputProvider(resumed_config.output_map_names)
+    resumed_output = MemoryRasterOutputProvider()
     sim_b = build_simulation(
         resumed_config,
         domain_5by5,
diff --git a/tests/test_hotstart_state_loading.py b/tests/test_hotstart_state_loading.py
index 2d2e7c0..eb1d258 100644
--- a/tests/test_hotstart_state_loading.py
+++ b/tests/test_hotstart_state_loading.py
@@ -196,7 +196,7 @@ class TestSimulationBuilderHotstart:
 
     @staticmethod
     def _create_hotstart_bytes(domain_5by5, sim_config: SimulationConfig) -> io.BytesIO:
-        raster_output = MemoryRasterOutputProvider(sim_config.output_map_names)
+        raster_output = MemoryRasterOutputProvider()
         simulation = (
             SimulationBuilder(sim_config, domain_5by5.arr_mask, np.float32)
             .with_domain_data(domain_5by5.domain_data)
@@ -217,7 +217,7 @@ def _build_with_hotstart(
         hotstart_bytes: io.BytesIO,
         domain_data: DomainData | None = None,
     ):
-        raster_output = MemoryRasterOutputProvider(sim_config.output_map_names)
+        raster_output = MemoryRasterOutputProvider()
         builder = (
             SimulationBuilder(sim_config, domain_5by5.arr_mask, np.float32)
             .with_domain_data(domain_data or domain_5by5.domain_data)
@@ -274,7 +274,7 @@ def test_with_hotstart_from_bytes(
         valid_hotstart_bytes: io.BytesIO,
     ) -> None:
         """Builder should store HotstartLoader from BytesIO."""
-        raster_output = MemoryRasterOutputProvider(sim_config.output_map_names)
+        raster_output = MemoryRasterOutputProvider()
         builder = (
             SimulationBuilder(sim_config, domain_5by5.arr_mask, np.float32)
             .with_domain_data(domain_5by5.domain_data)
@@ -298,7 +298,7 @@ def test_with_hotstart_from_file(
         valid_hotstart_bytes.seek(0)
         hotstart_file.write_bytes(valid_hotstart_bytes.read())
 
-        raster_output = MemoryRasterOutputProvider(sim_config.output_map_names)
+        raster_output = MemoryRasterOutputProvider()
         builder = (
             SimulationBuilder(sim_config, domain_5by5.arr_mask, np.float32)
             .with_domain_data(domain_5by5.domain_data)
@@ -607,7 +607,7 @@ def test_build_rejects_drainage_mismatch_hotstart_has_drainage(
             swmm_inp=None,  # No drainage
         )
 
-        raster_output = MemoryRasterOutputProvider(config_no_drainage.output_map_names)
+        raster_output = MemoryRasterOutputProvider()
 
         with pytest.raises(
             HotstartError, match="Hotstart contains drainage state but current configuration"
@@ -672,7 +672,7 @@ def test_build_rejects_drainage_mismatch_config_has_drainage(
             swmm_inp="fake.inp",  # Has drainage
         )
 
-        raster_output = MemoryRasterOutputProvider(config_with_drainage.output_map_names)
+        raster_output = MemoryRasterOutputProvider()
 
         with pytest.raises(
             HotstartError, match="Hotstart has no drainage state but current configuration"
diff --git a/tests/test_hotstart_timed_inputs.py b/tests/test_hotstart_timed_inputs.py
index 2f4a618..7ef6a02 100644
--- a/tests/test_hotstart_timed_inputs.py
+++ b/tests/test_hotstart_timed_inputs.py
@@ -237,7 +237,7 @@ def _build_provider_simulation(
     builder = (
         SimulationBuilder(sim_config, domain_5by5.arr_mask, np.float32)
         .with_input_provider(input_provider)
-        .with_raster_output_provider(MemoryRasterOutputProvider(sim_config.output_map_names))
+        .with_raster_output_provider(MemoryRasterOutputProvider())
         .with_vector_output_provider(MemoryVectorOutputProvider())
     )
     if hotstart_bytes is not None:
@@ -282,7 +282,7 @@ def _build_map_aware_provider_simulation(
     builder = (
         SimulationBuilder(sim_config, domain_5by5.arr_mask, np.float32)
         .with_input_provider(provider)
-        .with_raster_output_provider(MemoryRasterOutputProvider(sim_config.output_map_names))
+        .with_raster_output_provider(MemoryRasterOutputProvider())
         .with_vector_output_provider(MemoryVectorOutputProvider())
     )
     if hotstart_bytes is not None:
@@ -544,7 +544,7 @@ def test_resume_rejects_changed_input_map_without_provider(domain_5by5) -> None:
     builder = (
         SimulationBuilder(changed_config, domain_5by5.arr_mask, np.float32)
         .with_domain_data(domain_5by5.domain_data)
-        .with_raster_output_provider(MemoryRasterOutputProvider(changed_config.output_map_names))
+        .with_raster_output_provider(MemoryRasterOutputProvider())
         .with_vector_output_provider(MemoryVectorOutputProvider())
         .with_hotstart(hotstart_bytes)
     )
@@ -616,7 +616,7 @@ def test_resume_rejects_pending_timed_input_without_provider(domain_5by5) -> Non
     builder = (
         SimulationBuilder(sim_config, domain_5by5.arr_mask, np.float32)
         .with_domain_data(domain_5by5.domain_data)
-        .with_raster_output_provider(MemoryRasterOutputProvider(sim_config.output_map_names))
+        .with_raster_output_provider(MemoryRasterOutputProvider())
         .with_vector_output_provider(MemoryVectorOutputProvider())
         .with_hotstart(hotstart_bytes)
     )
diff --git a/tests/test_max_values.py b/tests/test_max_values.py
index 36140c6..2759c00 100644
--- a/tests/test_max_values.py
+++ b/tests/test_max_values.py
@@ -61,7 +61,7 @@ def sim_5by5_max_values(domain_5by5, helpers) -> Simulation:
     )
 
     # Create output provider
-    raster_output = MemoryRasterOutputProvider(sim_config.output_map_names)
+    raster_output = MemoryRasterOutputProvider()
 
     # Build simulation
     simulation = (
diff --git a/tests/test_rainfall_precision.py b/tests/test_rainfall_precision.py
index ef9605f..8856a37 100644
--- a/tests/test_rainfall_precision.py
+++ b/tests/test_rainfall_precision.py
@@ -126,7 +126,7 @@ def _run_rain_only_simulation(
     simulation = (
         SimulationBuilder(config, np.zeros(shape, dtype=np.bool_), dtype)
         .with_domain_data(domain_data)
-        .with_raster_output_provider(MemoryRasterOutputProvider(config.output_map_names))
+        .with_raster_output_provider(MemoryRasterOutputProvider())
         .with_vector_output_provider(MemoryVectorOutputProvider())
         .with_mass_balance_output_provider(mass_balance_output)
         .build()
@@ -175,7 +175,7 @@ def _run_combined_removal_simulation(
         infiltration_model=infiltration_model,
     )
     mass_balance_output = CaptureMassBalanceOutputProvider()
-    raster_output = MemoryRasterOutputProvider(output_map_names)
+    raster_output = MemoryRasterOutputProvider()
     dtype = np.float32
     simulation = (
         SimulationBuilder(config, np.zeros(shape, dtype=np.bool_), dtype)
diff --git a/tests/test_report.py b/tests/test_report.py
index 787e41a..279eb07 100644
--- a/tests/test_report.py
+++ b/tests/test_report.py
@@ -38,7 +38,7 @@
 def test_get_output_arrays_returns_a_fresh_selection() -> None:
     start_time = datetime(2000, 1, 1, tzinfo=UTC)
     out_map_names = {"water_depth": "depth", "max_water_depth": "depth_max"}
-    raster_provider = MemoryRasterOutputProvider(out_map_names)
+    raster_provider = MemoryRasterOutputProvider()
     report = Report(
         start_time=start_time,
         temporal_type=TemporalType.ABSOLUTE,
@@ -74,7 +74,7 @@ def test_get_output_arrays_returns_a_fresh_selection() -> None:
 def test_maxima_are_selected_independently_of_base_arrays() -> None:
     start_time = datetime(2000, 1, 1, tzinfo=UTC)
     out_map_names = {"max_water_depth": "depth_max", "max_flow_speed": "speed_max"}
-    raster_provider = MemoryRasterOutputProvider(out_map_names)
+    raster_provider = MemoryRasterOutputProvider()
     report = Report(
         start_time=start_time,
         temporal_type=TemporalType.ABSOLUTE,
@@ -117,7 +117,7 @@ def test_maxima_are_selected_independently_of_base_arrays() -> None:
 def test_flow_rate_outputs_use_committed_discharges() -> None:
     start_time = datetime(2000, 1, 1, tzinfo=UTC)
     out_map_names = {"flow_rate_x": "flow_x", "flow_rate_y": "flow_y"}
-    raster_provider = MemoryRasterOutputProvider(out_map_names)
+    raster_provider = MemoryRasterOutputProvider()
     report = Report(
         start_time=start_time,
         temporal_type=TemporalType.ABSOLUTE,
@@ -158,7 +158,7 @@ def test_flow_rate_outputs_use_committed_discharges() -> None:
 
 def test_drainage_topology_is_written_before_attributes() -> None:
     start_time = datetime(2000, 1, 1, tzinfo=UTC)
-    raster_provider = MemoryRasterOutputProvider({})
+    raster_provider = MemoryRasterOutputProvider()
     vector_provider = MemoryVectorOutputProvider()
     report = Report(
         start_time=start_time,
diff --git a/tests/test_stats.py b/tests/test_stats.py
index 1417f7d..af4312f 100644
--- a/tests/test_stats.py
+++ b/tests/test_stats.py
@@ -104,7 +104,7 @@ def sim_5by5_stats(domain_5by5, helpers, tmp_path_factory):
     )
 
     # Create output provider
-    raster_output = MemoryRasterOutputProvider(sim_config.output_map_names)
+    raster_output = MemoryRasterOutputProvider()
 
     # Build simulation
     simulation = (
@@ -297,7 +297,7 @@ def _run_timed_stats_simulation(
     simulation = (
         SimulationBuilder(sim_config, domain_5by5.arr_mask, np.float32)
         .with_input_provider(input_provider)
-        .with_raster_output_provider(MemoryRasterOutputProvider(sim_config.output_map_names))
+        .with_raster_output_provider(MemoryRasterOutputProvider())
         .with_vector_output_provider(MemoryVectorOutputProvider())
         .with_mass_balance_output_provider(CSVMassBalanceOutputProvider(file_name=str(stats_file)))
         .build()
diff --git a/tests/test_steep_plane.py b/tests/test_steep_plane.py
index a265f7c..42c0fbb 100644
--- a/tests/test_steep_plane.py
+++ b/tests/test_steep_plane.py
@@ -70,7 +70,7 @@ def _run_steep_plane(max_slope: float, stats_file: Path):
         infiltration_model=InfiltrationModelType.NULL,
     )
     array_mask = np.zeros((rows, cols), dtype=np.bool_)
-    raster_output = MemoryRasterOutputProvider(config.output_map_names)
+    raster_output = MemoryRasterOutputProvider()
     simulation = (
         SimulationBuilder(config, array_mask, np.float32)
         .with_domain_data(domain_data)
@@ -142,7 +142,7 @@ def _build_regime_switch_simulation(
         cols=cols,
         crs_wkt="",
     )
-    raster_output = MemoryRasterOutputProvider(config.output_map_names)
+    raster_output = MemoryRasterOutputProvider()
     builder = (
         SimulationBuilder(config, np.zeros((rows, cols), dtype=np.bool_), np.float32)
         .with_domain_data(domain_data)
diff --git a/tests/test_wse.py b/tests/test_wse.py
index 9580e55..496e27d 100644
--- a/tests/test_wse.py
+++ b/tests/test_wse.py
@@ -61,7 +61,7 @@ def sim_5by5_wse(domain_5by5, helpers) -> Simulation:
     )
 
     # Create output provider
-    raster_output = MemoryRasterOutputProvider(sim_config.output_map_names)
+    raster_output = MemoryRasterOutputProvider()
 
     # Build simulation
     simulation = (
@@ -185,7 +185,7 @@ def test_timed_memory_input_updates_water_depth_from_wse(domain_5by5) -> None:
             },
         }
     )
-    raster_output = MemoryRasterOutputProvider(sim_config.output_map_names)
+    raster_output = MemoryRasterOutputProvider()
     simulation = (
         SimulationBuilder(sim_config, domain_5by5.arr_mask, np.float32)
         .with_input_provider(input_provider)