diff --git a/airflow-core/src/airflow/partition_mappers/temporal.py b/airflow-core/src/airflow/partition_mappers/temporal.py
index 9c86bace56b42..d1a4c7c904868 100644
--- a/airflow-core/src/airflow/partition_mappers/temporal.py
+++ b/airflow-core/src/airflow/partition_mappers/temporal.py
@@ -18,10 +18,14 @@
 
 from abc import ABC, abstractmethod
 from datetime import datetime, timedelta
-from typing import Any
+from typing import TYPE_CHECKING, Any
 
+from airflow._shared.timezones.timezone import make_aware, parse_timezone
 from airflow.partition_mappers.base import PartitionMapper
 
+if TYPE_CHECKING:
+    from pendulum import FixedTimezone, Timezone
+
 
 class _BaseTemporalMapper(PartitionMapper, ABC):
     """Base class for Temporal Partition Mappers."""
@@ -30,14 +34,21 @@ class _BaseTemporalMapper(PartitionMapper, ABC):
 
     def __init__(
         self,
+        *,
+        timezone: str | Timezone | FixedTimezone = "UTC",
         input_format: str = "%Y-%m-%dT%H:%M:%S",
         output_format: str | None = None,
     ):
         self.input_format = input_format
         self.output_format = output_format or self.default_output_format
+        if isinstance(timezone, str):
+            timezone = parse_timezone(timezone)
+        self._timezone = timezone
 
     def to_downstream(self, key: str) -> str:
         dt = datetime.strptime(key, self.input_format)
+        if dt.tzinfo is None:
+            dt = make_aware(dt, self._timezone)
         normalized = self.normalize(dt)
         return self.format(normalized)
 
@@ -50,7 +61,10 @@ def format(self, dt: datetime) -> str:
         return dt.strftime(self.output_format)
 
     def serialize(self) -> dict[str, Any]:
+        from airflow.serialization.encoders import encode_timezone
+
         return {
+            "timezone": encode_timezone(self._timezone),
             "input_format": self.input_format,
             "output_format": self.output_format,
         }
@@ -58,6 +72,7 @@ def serialize(self) -> dict[str, Any]:
     @classmethod
     def deserialize(cls, data: dict[str, Any]) -> PartitionMapper:
         return cls(
+            timezone=parse_timezone(data.get("timezone", "UTC")),
             input_format=data["input_format"],
             output_format=data["output_format"],
         )
diff --git a/airflow-core/tests/unit/partition_mappers/test_temporal.py b/airflow-core/tests/unit/partition_mappers/test_temporal.py
index 89ad98cebbccc..c6b5b1d760d71 100644
--- a/airflow-core/tests/unit/partition_mappers/test_temporal.py
+++ b/airflow-core/tests/unit/partition_mappers/test_temporal.py
@@ -46,7 +46,7 @@ def test_to_downstream(
         mapper_cls: type[_BaseTemporalMapper],
         expected_downstream_key: str,
     ):
-        pm = mapper_cls()
+        pm = mapper_cls(timezone="UTC")
         assert pm.to_downstream("2026-02-10T14:30:45") == expected_downstream_key
 
     @pytest.mark.parametrize(
@@ -61,8 +61,9 @@ def test_to_downstream(
         ],
     )
     def test_serialize(self, mapper_cls: type[_BaseTemporalMapper], expected_outut_format: str):
-        pm = mapper_cls()
+        pm = mapper_cls(timezone="UTC")
         assert pm.serialize() == {
+            "timezone": "UTC",
             "input_format": "%Y-%m-%dT%H:%M:%S",
             "output_format": expected_outut_format,
         }
@@ -81,6 +82,7 @@ def test_serialize(self, mapper_cls: type[_BaseTemporalMapper], expected_outut_f
     def test_deserialize(self, mapper_cls):
         pm = mapper_cls.deserialize(
             {
+                "timezone": "UTC",
                 "input_format": "%Y-%m-%dT%H:%M:%S",
                 "output_format": "customized-format",
             }
@@ -88,3 +90,32 @@ def test_deserialize(self, mapper_cls):
         assert isinstance(pm, mapper_cls)
         assert pm.input_format == "%Y-%m-%dT%H:%M:%S"
         assert pm.output_format == "customized-format"
+
+    @pytest.mark.parametrize(
+        "mapper_cls",
+        [
+            StartOfHourMapper,
+            StartOfDayMapper,
+            StartOfWeekMapper,
+            StartOfMonthMapper,
+            StartOfQuarterMapper,
+            StartOfYearMapper,
+        ],
+    )
+    def test_deserialize_legacy_no_timezone(self, mapper_cls):
+        """Deserializing data without a timezone key defaults to UTC."""
+        pm = mapper_cls.deserialize(
+            {
+                "input_format": "%Y-%m-%dT%H:%M:%S",
+                "output_format": "customized-format",
+            }
+        )
+        assert isinstance(pm, mapper_cls)
+
+    def test_to_downstream_timezone_aware(self):
+        """Input is interpreted as local time in the given timezone."""
+        pm = StartOfDayMapper(timezone="America/New_York")
+        # 2026-02-10T23:00:00 in New York local time → start-of-day is 2026-02-10
+        assert pm.to_downstream("2026-02-10T23:00:00") == "2026-02-10"
+        # 2026-02-11T01:00:00 in New York local time → start-of-day is 2026-02-11
+        assert pm.to_downstream("2026-02-11T01:00:00") == "2026-02-11"