Enhancing the modularity and interoperability of hydrologic models: A demonstration with the Structure for Unifying Multiple Modeling Alternatives (SUMMA)

Abstract

We present a general approach to improve the modularity and interoperability of hydrologic and land models, demonstrated through refactoring the Structure for Unifying Multiple Modeling Alternatives (SUMMA) model. We first present a general hierarchical structure to organize the model source code, representing the horizontal variability across the domain (i.e., the “hydrofabric” of sub-basins) as well as the vertical architecture where each sub-basin is represented by vertical columns that extend from the top of the vegetation canopy to the depth of active groundwater. We then present a flexible strategy to solve the coupled conservation equations for water and energy in each vertical column, refactoring SUMMA’s operator-splitting methods, non-linear solvers, and flux calculators. Modularity was improved using internal subroutines and classes, and interoperability was improved using the initialize–update–finalize sequence at fine granularity. These refactoring developments support the use of Basic Model Interface (BMI) functions, improving component reusability, extensibility, and maintainability.