# Modules

SPHY enables the user to turn on/off modules (processes) that are relevant/irrelevant for the area of interest. 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. The advantages of turning off irrelevant modules are two-fold: (i) decrease model run time, and (ii) decrease the number of required model input data. It should be noted, however, that the hydrologic model structure should be specific to the catchment’s characteristics (Pomeroy et al. 2007; Clark et al. 2008; Niu et al. 2011; Essery et al. 2013; Clark et al., 2015a, 2015b). It is therefore essential that the user knows which catchment characteristics and processes should be included in their modeling framework.

Figure 3 represents an overview of the six modules available: glaciers, snow, groundwater, dynamic vegetation, simple routing, lake/reservoir routing, soil erosion and sediment transport. All modules can run independently of each other, except for the glacier module. If glaciers are present, then snow processes are relevant as well (Verbunt et al. 2003; Singh and Kumar 1997). Since melting glacier water percolates to the groundwater layer, the glacier module cannot run with the groundwater module turned off. Two modules are available for runoff routing: (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 following sections.

![Figure 3: Modules of the SPHY model that can be switched on/off.](https://2432255304-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FbpkOf6MyIYzEi0TyV0In%2Fuploads%2FzcWuNPcounCEuhP018fG%2F5.png?alt=media)
