SPHY enables the user to turn on/off modules that are not required. This concept is very useful if the user is studying hydrological processes in regions where not all hydrological processes are relevant. A user may for example be interested in studying irrigation water requirements in central Africa. For this region glacier and snow melting processes are irrelevant, and can thus be switched off. Another user may only be interested in simulating moisture conditions in the first soil layer, allowing the possibility to switch off the routing and groundwater modules. The advantages of turning off irrelevant modules are two-fold: (i) decrease model run-time, and (ii) decrease the amount of required model input data.
The figure represents an overview of the six modules available: glaciers, snow, groundwater, dynamic vegetation, simple routing, and lake/reservoir routing. All modules can run independently from each other, except for the glacier module. If glaciers are present, then snow processes are relevant as well, meaning that the snow module is turned on automatically if the glacier module is turned on. Since melting glacier water percolates to the groundwater store, the glacier module cannot run with the groundwater module turned off. For routing two modules are available, being (i) a simple flow accumulation routing scheme, and (ii) a fractional flow accumulation routing scheme used when lakes/reservoirs are present. The user has the option to turn off routing, or to choose between one of these two routing modules. All hydrological processes incorporated in the SPHY model are described in detail in the peer-reviewed publication introducing the SPHY model.