WSIMOD

Summary

The water cycle is highly interconnected; water fluxes in one part depend on physical and human processes throughout. For example, rivers are a water supply, a receiver of wastewater, and an aggregate of many hydrological, biological, and chemical processes. Thus, simulations of the water cycle that have highly constrained boundaries may miss key interactions that create unanticipated impacts or unexpected opportunities. Integrated environmental models aim to resolve the issue of boundary conditions, however they have some key limitations, and in particular there is a significant need for a parsimonious, self-contained suite that is accessible and easy to set up.

Statement of need

Traditional approaches to water system modelling broadly fall into highly numerical models that excel in representing individual subsystems, or systems-dynamics models that create broad representations but lack a physical basis. Early attempts at a physical representation of the water cycle combined existing numerical models through an integration framework. While successful, this approach has an incredibly high user burden because each subsystem model is so detailed, and as a consequence is also difficult to customise. For example, SWAT is widely used for rural water cycle modelling, while SWMM is commonly used for urban water cycle modelling. These two tools can be linked through integration frameworks. Despite the apparent power of combining two widely adopted models, integrated applications have been limited, likely due to the same issues noted above: user burden and difficulty of customisation.

Because of this need, we provide a parsimonious and self-contained suite for integrated water-cycle modelling in the WSIMOD Python package. It brings together software developed over three years on the CAMELLIA project. Urban water processes are based on those implemented and validated in the CityWat model, while hydrological and agricultural processes are based on the CatchWat model. WSIMOD also provides an interface for message passing between different model components, enabling all parts of the water cycle to interact. The result is a simulation model that is easy to set up, highly flexible, and ideal for representing water quality and quantity in “non-textbook” water systems.

The package includes tutorials and examples to help modellers create nodes (representing subsystems), connect them with arcs (representing fluxes), and orchestrate them into a working simulation model.