## 4 Results
### Definition of Snowpack Wet-Snow Dynamics
#### 4.1.1 Local Scale: Backscatter Signal Understanding
The \(\Delta\sigma\) signal was not able to capture the onset of the melting runoff of this cycle since it occurred in the period between images. For the last cycle of this year, wet snow was present since the beginning of the cycle due to higher temperatures during this period. Two LMs were found, while the melting onset started on the 5 April, with LM3 (\(-\)11.57 dB), in which the snowpack was cooled by a snowfall event that made the appearance of another local minimum LM4 (\(-\)9.81 dB) that finally triggered the spring melting. The third analyzed year, 2018-2019 (Figure 4c), was the driest of the analyzed ones. Seven short melting cycles were identified. One LM is defined in each of them. All LMs follow the same dynamics, quick melting after a light snowfall. The first cycle was so quick that the \(\Delta\sigma\) signal was not able to capture the presence of wet snow. That is, LM1 was above the wet-snow threshold of \(-\)3.00 dB. The \(\Delta\sigma\) signal reached values of \(-\)3.63 dB for LM2 and \(-\)7.86 dB for LM3, and the \(\Delta\sigma\) rapidly recovered its values by the time the snow cover disappeared. Then, between late January and February, two LMs were identified, LM4 (\(-\)4.21 dB) and LM5 (\(-\)5.81 dB). LM6 (\(-\)5.85 dB) can be identified as an actual spring melting runoff onset since the length of this melting cycle is the longest and the accumulated snow was the highest of the year. Finally, the last LM occurred during April LM7 (\(-\)5.97 dB) was triggered again by an energy exchange between the snowpack and the ground, demonstrated by higher temperatures that heated the ground. * Local Minima Classification  
The previous analysis of \(\Delta\sigma\) signals evolution on a local scale and the identification of different LMs allowed for an explanation of their evolution in relation to snowpack dynamics over these areas. Starting with the hypothesis that a LM triggers the onset of melting runoff and the four types of melting cycles identified by [3] for the study area, four types of LMs in the \(\Delta\sigma\) signal were identified (Table 2 and Figure 5). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Type I** & **Type II** & **Type III** & **Type IV** \\ \hline LM4 2016–2017 & LM1, LM2, LM3, & LM1 2017–2018 & LM6 2016–2017 \\ LM4 2017–2018 & LM2, LM3 2017–2018 & LM1, LM4 2018–2019 & LM7 2018–2019 \\ LM3, LM6 2018–2019 & LM2, LM6 2018–2019 & & LM7 2018–2019 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Local scale classification of LMs based on the four LM types explained in Figure 5.  
* Local Minimum Type I: the LM is found at the end of a well-developed snowpack. It is representative of long-lasting snow cycles, with a large amount of snow, resulting from a long accumulation phase, and it is associated with a very compact state of the snow with a high level of metamorphism. This LM is found in melting cycles described by depletion curve Type I in [3];
* Local Minimum Type II: the LM is not unique in the snow cycle. It describes a quick melting period that is stopped by another snowfall or cold period that retreezes snow. This LM is found in melting cycles described by depletion curve Type II in [3];
* Local Minimum Type III: the LM is unique within the melting cycle, that is, before and after this LM there is no snow. In addition, it takes place at the beginning of the snow season, when the energy exchange between the snowpack and the ground causes liquid water content to increase. This LM is found in melting cycles described by depletion curve Type III in [3];
* Local Minimum Type IV: as in the previous case, the LM is singular, meaning that there is no snow before or after this particular LM. However, in this case, the minimum appears in sporadic snow cycles that occur during late winter or spring, and always after the main melting cycle. The LM is connected to a melting trigger by an increase in the temperature and incoming flux of shortwave radiation. This LM is found in melting cycles described by depletion curve IV in [3].