Basic Model Interface (BMI)

Introduction

The Community Surface Dynamics Modeling System (CSMDS) has developed the Basic Model Interface (BMI). BMI consists of a set of standard control and query functions that can be added by a developer to the model code and makes a model both easier to learn and easier to couple with other software elements.

For more information see also: http://csdms.colorado.edu/wiki/BMI_Description

CSDMS provides specifications for the languages C, C++, Fortran and Python. Wflow, written in the Julia programming language, makes use of the following Julia specification, based on BMI 2.0 version.

For the BMI implementation of wflow all grids are defined as unstructured grids, including the special cases scalar and points. While the input (forcing and model parameters) is structured (uniform rectilinear), internally wflow works with one dimensional arrays based on the active grid cells of the 2D model domain.

Configuration

The variables that wflow can exchange through BMI are model state and output variables. The standard names of these variables based on CSDMS Standard Names should be listed below the API section in the variables list of the TOML configuration file. Below an example of this API section, that lists the variables that wflow can exchange through BMI:

[API]
variables = [
   "river_water__volume_flow_rate",
   "soil_water_unsat-zone__depth",
   "soil_water__transpiration_volume_flux",
   "soil_layer~1_water_unsat-zone__depth",
   "soil_layer~2_water_unsat-zone__depth",
   "soil_layer~3_water_unsat-zone__depth",
   "soil_layer~4_water_unsat-zone__depth",
]

Variables with a third dimension, for example layer as part of the SBM soil model, are exposed as two-dimensional grids through the wflow BMI implementation. For these variables the index of this third dimension is required, by adding k to the layer part of the variable standard name (k refers to the index of the third dimension): layer~k. For example, the variable soil_layer~1_water_unsat-zone__depth refers to the amount of water in the unsaturated store of the first soil layer of the SBM soil model.

The model state and output variable standard names are provided in the “Model parameters and variables” section of the Model documentation.

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