## 3 Methods  
The Los Hoyos and Papuos streams were inspected along their whole length using proper canyoneering techniques during the several days after the flash flood. An immediate field survey was made after the fatal event to collect information about high water marks (HWM, i.e., flotsam; the floating elements left by the flash flood) and other flood markers such as vegetation bent by the river flow. During the inspection of both rivers, the presence of favorable sites for calculating the flow more accurately were identified, searching for evidence of the type of flooding: ordinary flood, hyperconcentrated, or debris flow, and specific problems such as a log dam. Precipitation data were obtained from the Spanish weather forecasting agency (AEMET). Spatial information (slope map, distances, concentration times, land cover) was calculated using ArcGIS (ESRI: Redlands, CA, USA) software. A first simple hydrological approach (rational \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Basin**} & **Average** & \multicolumn{2}{c}{**Area of Flash**} & \multirow{2}{*}{**P2/P500**} & **Q2/Q500** & \multirow{2}{*}{**Land Cover 4**} & **\% of Total** \\  & **Slope/Canyon** & & & **(km2) 1** & & **(mm) 2** & **(m3 s-1) 3** & **Area Bumped** \\ \hline Hoyos R. & 0.26/0.18 & 4.2 & 4.1 & 69/214 & 10/57 & R, C, P & 74 \\ Papuos R. & 0.22/0.20 & 15.3 & 7.6 & 66/203 & 14/79 & R, C, P, F & 42 \\ \hline \hline \end{tabular} Notes: 1 Area with flash flood arrival point. 2 Estimated precipitation for the return periods of 2 and 500 years. 3 Estimated discharge for the return periods of 2 and 500 years. 4 R: _Quercus robur_ and pine trees, C: cherry orchards, P: alpine pastures, F: old, fired lands.  
\end{table} 
Table 1: General data for the two basins studied. Figure 3: Slope map of the basin and burned surfaces affected by the 2017 wildfire. method) was used to calculate the discharge related to return period intervals. Furthermore, a full hydrological model simulation was created in order to calculate the maximum discharge of the 2017 event by means of HEC-HMS (CEIWR-HEC: Davis, CA, USA) software. Comparative floodwater height evidence along the Los Hoyos and Papuos streams was collected, using the method of critical point calculation discharge (Figure 4A). The maximum water height was used in hydraulic calculations to obtain the approximate discharge. The basin model used in the HEC-HMS software was derived from a 5 m Digital Elevation Model (DEM). Disaggregation was based on the spatial distribution of the physiographic factors that determine a homogenous hydrologic response (i.e., lithology, soils, cover type, hydrologic conditions, and slope), which divide the Hoyos and Papuos basins into 3 and 11 sub-basins, respectively. The use of simulation methods for the various processes involved was based on the information available for the basin (no flow data are available for the Hoyos and Papuos basins). The use of the SCS-CN loss method, which is well developed and widely accepted in the USA and other countries [10; 11; 12], was based on the availability of data sources for each necessary parameter (surface slope, soil hydrological conditions, and land use); and also on the possibility for conducting fieldwork to test and adjust the values that were previously obtained by photointerpretation. The absence of rainfall and flow data associated with the same event reduces the availability of transformation methods in the HEC-HMS environment to only two options, so the runoff hydrograph was obtained using the Clark unit hydrograph [13] with estimated concentration time (Tc) and storage coefficients. The time of concentration was derived using the Temez formula, which depends on the length of the main channel for each sub-basin and its slope [14]. The storage coefficient was calculated, assuming that it represents 0.6 Tc. The Muskingum-Cunge method was implemented for flood wave routing [15], due to the absence of observed flow data for the rainfall event.