## 4 Results  
### Definition of Snowpack Wet-Snow Dynamics  
#### 4.1.1 Local Scale: Backscatter Signal Understanding  
On a local scale, the connection between the SAR backscattering signal and snow dynamics was explored during the three hydrological years: 2016-2017, 2017-2018, and 2018-2019. Meteorological information and terrestrial photography at the Refugio Poqueira weather station were used in this process. Annual snowfall values varied between years, with 394 mm, 384 mm, and 244 mm, respectively. Temperature patterns also changed during years, with annual mean daily values of 7.5 \({}^{\circ}\)C, 6.1 \({}^{\circ}\)C, and 7.4 \({}^{\circ}\)C, for each hydrological year in the study period, respectively (Figure 4a-c, upper panel). This variability implies that the number of snow cycles also varies in each of the analyzed years. These snow dynamics were defined by combining terrestrial photography (changes in the snowpack) and meteorological information (snowmelt events) on a daily scale at the target area (see Section 3.1.2). Figure 4 shows lines in the top and bottom of each gray rectangle identifying an accumulation (blue) or melting (red) phase of each of this snow cycle (Figure 4, gray rectangles). Figure 4: Temporal evolution of analyzed variables for three hydrological years: (**a**) 2016–2017, (**b**) 2017–2018, (**c**) 2018–2019. For each year: (i) the upper panel shows precipitation (blue bars) and snowfalls (gray bars) evolution; (ii) the intermediate panel represents the temporal evolution of daily temperatures, maximum (red), mean (orange) and minimum (blue); (iii) the bottom panel shows the evolution of the difference backscattering between the reference image and the day of interest. (red line with triangles). The circled numbers in the bottom panel represent each of the local minima analyzed. The dashed line in the bottom panel marks the wet-snow threshold defined for the study area. In all panels, the presence of snow in the study area is highlighted by using a gray rectangle; lines in the top and bottom of this rectangle identify an accumulation (blue) or melting (red) phase. In 2016-2017 (Figure 4a), six LMs were identified, four in the first melting cycle, one in the second cycle, and another one in the third. LM1 (\(-\)4.11 dB) was found in the third week of November corresponding to the beginning of the snow season. At this stage, the energy exchange between the snowpack and the ground increased the liquid water content of the snowpack, reaching this local minimum in the \(\Delta\sigma\) signal. Water content highly increased in LM2 (\(-\)8.83 dB), 5 December, with the lower \(\Delta\sigma\) value of the year. This LM was preceded by a significant snowfall period, which was followed by a rain-on-snow event and an increment of the temperature that increased the water content again. The coolest period occurred after that, which made the snowpack to dry out. A significant increase in temperatures provoked LM3 (\(-\)3.62 dB) in the second week of December. Again, a cool period stabilized the signal until the combination of precipitation and increasing temperatures generated LM4 (\(-\)6.40 dB), on the 21 st of February, which can be defined as the onset of spring melting runoff. LM5 (\(-\)4.11 dB) and LM6 (\(-\)5.21 dB) corresponded to faster melting cycles, whose shallow snowpack provoked a quick melting due to the energy exchanges between the snowpack and the ground. For the second analyzed year, 2017-2018 (Figure 4b), four LMs were identified, one in the first melting cycle, one in the second cycle, and two in the third one. The first local minimum LM1 (\(-\)4.70 dB) was found in mid-December and corresponded to a shallow snowpack that quickly melted after a light snowfall. For the second melting cycle, liquid water content increases in LM2 (\(-\)4.36 dB) corresponding to an increase of the temperatures. However, the melting did not continue since the temperature dropped again.