diff --git a/docs/input_requirement.md b/docs/input_requirement.md
index d59d18b..f73a135 100644
--- a/docs/input_requirement.md
+++ b/docs/input_requirement.md
@@ -100,7 +100,7 @@ Each variable declares the following properties:
 | `max_nan`      | `int`  | both          | The model's **tolerance**: max NaNs it can cope with in the series (must be >= 0). **SAP3 enforces this as a pre-`predict` gate** — if exceeded, the model is not called and the station is failed (`DATA_AVAILABILITY`); within tolerance, residual NaNs are delivered **as-is** for the model to handle (decision 1.13). |
 | `ensemble_mode`| `EnsembleMode` | future_known  | Whether ensemble or single traces are needed (`single` or `ensemble`, default: `single`) |
 | `unit`         | `Unit` | both          | **Required.** The physical unit the model expects this variable in (e.g. `Unit.MM_PER_DAY`). The delivered series is tagged with its unit and delivered **in the declared unit, or rejected loudly at integration** — no data without units. (Automatic unit conversion is a future adapter feature.) |
-| `aggregation`  | `AggregationMethod \| None` | both | **Optional.** `SUM` or `MEAN`, used when the declared resolution is coarser than the delivered data. Defaults to the per-parameter convention (precipitation / reference_et = `SUM`; state variables = `MEAN`); declare only to override. |
+| `aggregation`  | `AggregationMethod \| None` | both | **Optional.** `SUM`, `MEAN` or `MAX`, used when the declared resolution is coarser than the delivered data. Defaults to the per-parameter convention (precipitation / reference_et = `SUM`; state variables = `MEAN`); declare only to override. |
 
 ---
 
@@ -112,7 +112,7 @@ These three are a single coherent concern (mirroring SAP3's `ParameterDefinition
 
 **Units.** Every input variable declares the `unit` it expects (see properties table); outputs declare units via `TargetSpec` / `VariableMetadata`. The `Unit` enum must cover every parameter's unit and is a **sync contract with SAP3's `ParameterDefinition` units** — extended as needed (current additions for forcing: `PERCENT`, `M_PER_S`, `DEGREE`, `W_PER_M2`, `MM_PER_HOUR`).
 
-**Aggregation.** When a model declares a variable at a resolution coarser than the delivered data, SAP3 aggregates with `SUM` or `MEAN`. Default follows the per-parameter convention (precipitation / reference_et = `SUM`; temperature, discharge, SWE and other state variables = `MEAN`); override via the optional `aggregation` property only for a non-default rule.
+**Aggregation.** When a model declares a variable at a resolution coarser than the delivered data, SAP3 aggregates with `SUM`, `MEAN` or `MAX` (`MAX` for peak channels, e.g. a window-max discharge a flood threshold is set on). Default follows the per-parameter convention (precipitation / reference_et = `SUM`; temperature, discharge, SWE and other state variables = `MEAN`); override via the optional `aggregation` property only for a non-default rule.
 
 ## Static Inputs
 
diff --git a/forecast_interface/__init__.py b/forecast_interface/__init__.py
index ba93093..ccd7284 100644
--- a/forecast_interface/__init__.py
+++ b/forecast_interface/__init__.py
@@ -1,4 +1,4 @@
-__version__ = "0.1.18"
+__version__ = "0.1.19"
 
 from .common import AggregationMethod
 from .input import (
diff --git a/forecast_interface/common/aggregation.py b/forecast_interface/common/aggregation.py
index dc6df68..6e6f3f1 100644
--- a/forecast_interface/common/aggregation.py
+++ b/forecast_interface/common/aggregation.py
@@ -4,3 +4,4 @@
 class AggregationMethod(Enum):
     SUM = "sum"
     MEAN = "mean"
+    MAX = "max"
diff --git a/pyproject.toml b/pyproject.toml
index 51edc08..864eba6 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,6 @@
 [project]
 name = "forecastinterface"
-version = "0.1.18"
+version = "0.1.19"
 description = "Add your description here"
 readme = "README.md"
 requires-python = ">=3.11"
@@ -25,7 +25,7 @@ init_typed = true
 warn_required_dynamic_aliases = true
 
 [tool.bumpversion]
-current_version = "0.1.18"
+current_version = "0.1.19"
 commit = false
 tag = false
 allow_dirty = true
diff --git a/tests/test_output.py b/tests/test_output.py
index 26df01c..f658eba 100644
--- a/tests/test_output.py
+++ b/tests/test_output.py
@@ -72,9 +72,10 @@ class TestAggregationMethod:
     def test_members_exist(self) -> None:
         assert AggregationMethod.SUM.value == "sum"
         assert AggregationMethod.MEAN.value == "mean"
+        assert AggregationMethod.MAX.value == "max"
 
     def test_member_count(self) -> None:
-        assert len(AggregationMethod) == 2
+        assert len(AggregationMethod) == 3
 
 
 class TestVariableStatus:
diff --git a/uv.lock b/uv.lock
index 03ddebc..39aee7b 100644
--- a/uv.lock
+++ b/uv.lock
@@ -129,7 +129,7 @@ wheels = [
 
 [[package]]
 name = "forecastinterface"
-version = "0.1.18"
+version = "0.1.19"
 source = { virtual = "." }
 dependencies = [
     { name = "polars" },