Model Variables
Model variables describe the quantities used by APSIM Next Generation to represent the state, structure, or behaviour of each model component.
They can represent measurable properties (e.g., leaf area, soil water content) or control parameters (e.g., growth rate factors).
This page explains how variables are classified and used throughout the APSIM framework.
Overview
Each component in APSIM NG exchanges information through well-defined variables.
Some variables can be adjusted by users in the simulation configuration to modify behaviour, while others are produced by the model as results of internal calculations.
Together, they form the scientific link between model structure, parameterisation, and output.
Types of Variables
| Variable Type | Description | Example |
|---|---|---|
| Configurable Variables | Inputs that can be adjusted by users to change how the model behaves. They represent experimentally or genetically determined traits, constants, or settings. | Maximum leaf area, specific leaf weight, soil depth |
| Calculated (Reportable) Variables | Quantities derived by the model during simulation. These are read-only and can be reported in outputs or used by other models. | Leaf area index (LAI), soil water potential, biomass accumulation |
| Derived Functions | Quantities calculated continuously from other variables, often expressed as empirical or mechanistic equations. | Radiation use efficiency, temperature response function |