Enhanced model flexibility and coupling opportunities: The WetSpa model case

In the last decade spatially distributed hydrological models have becomeincreasingly versatile due to the improvements in computational capabilities, theavailability of digital data, and the use of Geographical Information System (GIS).Keeping up with technological development and new data types is becoming achallenge. Moreover, models are often developed to answer a specific need andthus lack flexibility, making it nearly impossible to further develop them. Using theprinciple of adaptability and expandability, we discuss an object oriented, modularmodel that is based on the fully distributed and physically based hydrological modelWetSpa. The original WetSpa model has been disassembled into smaller andindependent modules and it has been rewritten using the open source computerlanguage Python. In the new structure three main components are identified: (1) apre-process component for GIS maps preparation; (2) a Unit Class, representingthe watershed discretized in raster cells or physical based objects; and (3) a ModelControl Class, which organizes input/outputs and gives commands to the objectsunit. The physically based processes, such as runoff, infiltration, interception, etc.,are coded in separate scripts and organized via the Model Control Class. Thisapproach allows the user to select which processes will be simulated and in whichorder, as well as to evaluate the impact of different parameterizations of the sameprocess. The new model, WetSpaOO (Object Oriented) has been successfullytested on a theoretical case and, thanks to this new flexible structure, it has beencoupled with the groundwater flow model MODFLOW.