# Investigation of Rain-On-Snow Floods under Climate Change
## 2 Materials and Methods
### Hydrological Model  
In this study we applied the lumped conceptual hydrological model named Genie Rural a 6 parametres Journalier (GR6J) with snow module CemaNeige (e.g., [14; 15; 16; 17; 18]). The CemaNeige GR6J model version is implemented in airGR package [19; 20] of R software [21], which was applied in this study. The GR6J model version without the snow module only requires rainfall and evapotranspiration data to calculate runoff using six parameters (e.g., [14]). The equation proposed by [22] was applied to  
\begin{table}
\begin{tabular}{l c c c} \hline \hline
**Gauge Station** & **Kr\(\check{\text{s}}\)ovec** & **S\(\check{\text{o}}\)kava** & **Dvor** \\ \hline
**River** & \(\check{\text{s}}\)o\(\check{\text{a}}\) & **S\(\check{\text{a}}\)vinja** & **Gradas\(\check{\text{c}}\)ica** \\ \hline Catchment area [km\({}^{2}\)] & 157.9 & 63.4 & 78.9 \\ Mean catchment elevation [m] & 1376 & 1229 & 615 \\ Maximum catchment elevation [m] & 2533 & 2345 & 986 \\ Calibration period [dd/mm/yy] & 01/01/1964–31/12/2000 & 01/01/1964–31/12/2002 & 01/01/1981–31/12/2005 \\ Validation period [dd/mm/yy] & 01/01/2001–31/12/2011 & 01/01/2003–31/12/2013 & 01/01/2006-31/12/2016 \\ Minimum [m\({}^{3}\)/s] & 17. & 0.2 & 0.3 \\ Mean [m\({}^{2}\)/s] & 11.4 & 2.1 & 2.3 \\ Maximum [m\({}^{3}\)/s] & 195 & 99.9 & 55.6 \\ Standard deviation [m\({}^{3}\)/s] & 11.5 & 2.4 & 3.1 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Basic characteristics of the selected case studies and discharge data used.  
Figure 1: Location of the selected catchments (red border), meteorological stations (yellow crosses), discharge gauging stations (pink arrows) on the topographic map of Slovenia.  
calculate the potential evapotranspiration used as an input to the hydrological model in this study. In addition, the CemaNeige snow module requires also air temperature data and the catchment hypsometric curve and adds two more parameters to the GR6] model version (i.e., eight parameters in total). In [14; 23], detailed descriptions of the GR4] and GR6] model versions with equations and model structures were provided. Based on the catchment hypsometric curve, the CemaNeige snow module divides a catchment into five elevation zones that have equal areas. The snow module only uses precipitation and air temperature data as an input [15; 16]. Precipitation and air temperature data are extrapolated for each elevation zone and the differentiation between solid and liquid precipitation is carried out. Each elevation zone has one conceptual store that represents the snow cover, and only solid precipitation is used as an input to this store [15; 16]. Furthermore, the transfer function is used that enables the model to calculate the melted water from the conceptual snow store. This water is added to the liquid part of the precipitation and then further for runoff calculations [15; 16]. In [15; 16], a detailed description of the CemaNeige snow module was provided, which was also used in this study together with the GR6] model version. The method proposed by [24], which is also implemented in the airGR package, was applied to calibrate the hydrological model [19; 20]. In order to evaluate the calibration and validation performance of the hydrological model, the root mean square error (RMSE) and Nash-Sutcliffe efficiency (NSE) criteria [25] were used, which are, beside the visual inspection, the most widely used model performance criteria in hydrological applications [26].