diff --git a/CHANGELOG.md b/CHANGELOG.md
index a5f56cec..ab038331 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -26,7 +26,8 @@
   incorrectly labelling Walloon elevations as TAW.
 - Made terrain readiness fail closed on both the source raster and its valid
   SHA-256 sidecar, wrote provisioning evidence atomically, and corrected the
-  persisted acquisition interval to the canonical `period` granularity.
+  persisted acquisition interval to the canonical `period` granularity with a
+  stable spatial series key.
 - Extended detection-model capabilities with machine-readable training scope,
   validation scope, validated regions, national-validation status and the
   operator-review requirement. The configured local model remains bound to
diff --git a/backend/app/services/spw_terrain_service.py b/backend/app/services/spw_terrain_service.py
index 002bbcea..69134eef 100644
--- a/backend/app/services/spw_terrain_service.py
+++ b/backend/app/services/spw_terrain_service.py
@@ -418,6 +418,7 @@ class SpwTerrainService:
             content=content,
             source="SPW Relief de la Wallonie MNT 2021-2022 operator-provisioned GeoTIFF",
             source_name=SpwTerrainService.PROVIDER,
+            temporal_series_key=f"spw:terrain:mnt:{request_hash[:24]}",
             observed_at=datetime(2022, 3, 5, 23, 59, 59, tzinfo=UTC),
             valid_from=datetime(2021, 2, 19, tzinfo=UTC),
             valid_to=datetime(2022, 3, 5, 23, 59, 59, tzinfo=UTC),
diff --git a/backend/tests/test_spw_terrain_service.py b/backend/tests/test_spw_terrain_service.py
index 95371335..59c82625 100644
--- a/backend/tests/test_spw_terrain_service.py
+++ b/backend/tests/test_spw_terrain_service.py
@@ -164,8 +164,18 @@ def test_spw_terrain_acquisition_persists_bounded_dng_raster_and_provenance(
     assert captured["source_metadata"]["coverage_zones"] == ["wallonia"]
     assert captured["provenance_metadata"]["resampling"] == "bilinear"
     assert captured["provenance_metadata"]["source_sha256"] == source_digest
+    assert captured["temporal_series_key"].startswith("spw:terrain:mnt:")
     assert captured["temporal_granularity"] == "period"
     assert captured["valid_from"].date().isoformat() == "2021-02-19"
+    temporal = DatasetService._validate_temporal_metadata(
+        temporal_series_key=captured["temporal_series_key"],
+        observed_at=captured["observed_at"],
+        valid_from=captured["valid_from"],
+        valid_to=captured["valid_to"],
+        temporal_granularity=captured["temporal_granularity"],
+        source_version=captured["source_version"],
+    )
+    assert temporal["temporal_granularity"] == "period"
     with rasterio.MemoryFile(captured["content"]) as memory:
         with memory.open() as derived:
             assert derived.crs.to_epsg() == 3812
diff --git a/docs/CODEX_EXECUTION_LOG.md b/docs/CODEX_EXECUTION_LOG.md
index ba0557b0..daa5710a 100644
--- a/docs/CODEX_EXECUTION_LOG.md
+++ b/docs/CODEX_EXECUTION_LOG.md
@@ -11193,7 +11193,7 @@ Implemented and verified:
   retained the source raster, checksum sidecar and atomic provisioning report;
 - made terrain availability fail closed until both raster and valid SHA-256
   sidecar exist, and persisted the official 2021-02-19/2022-03-05 observation
-  interval using the canonical `period` granularity;
+  interval using the canonical `period` granularity and spatial series key;
 - constrained AI capability claims to the actual Mol/Kempen evidence through
   machine-readable training/validation scope, `nationally_validated=false` and
   mandatory operator review. No national training result was fabricated.