## 2 Study Site and Available Data  
### The Sierra Nevada Mountain Range  
The Sierra Nevada mountain range (southern Spain, Figure 1a) is the southernmost mountain range in Europe, with elevations that reach 3479 m a.s.l. and this is only overcome by the European Alps. It covers approximately 80 km long in the East-West direction and 27 km wide in the North-South direction (Figure 1b). Alpine and Mediterranean climates coexist in the range. The alpine climate of high altitudes is modified by the proximity to the seacoast together with an abrupt topography, high radiation rates, and low relative humidity. The precipitation regime is highly variable, with annual precipitation values that can vary from dry years, with 200 mm of total precipitation, to wet years, with almost 1000 mm [2]. Regarding temperature, the annual mean daily temperature in the area is about 12.6 \({}^{\circ}\)C, with minimum daily temperatures staying above freezing from April to November [62]. Snow in the range frequently appears above 2000 m a.s.l. between October and May. Mediterranean boundary conditions deeply affect snow characteristics, remarkably so in the southern face of the range. Among these characteristics, the shallow and high-density snowpacks [63], the high evaposublimation rates [6], and the appearance of more than one accumulation-melting cycle during the snow season [3] are the ones that stand out the most. Streamflow in the downstream catchments is highly conditioned by these snow dynamics. Streamflow usually has several peaks linked to each one of the accumulation-melting cycles. Low, creeping vegetation and shrubs are the main vegetation in the area, particularly at upper altitudes. The _Hormathophylula spinosa_, the _Genista versicolor_, and the _Festuca clementei_ are the most common shrub types in the mountain range. Forestry high vegetation such as pine trees is not very common and can be found only in some reforested isolated pieces of land. All these physical and specific characteristics make the Sierra Nevada one of the most important centers of biodiversity in the Mediterranean regions. Thus, this region was declared UNESCO Biosphere Reserve in 1986, Natural Park in 1989, and National Park in 1999. Within the Sierra Nevada mountain range, this study was carried out with two different scales by using two study sites:  
* Plot scale--The Refugio Poqueira experimental site (Figure 1c, yellow cross). This area was selected to understand the connection between backscatter signals and snow dynamics. It is located at 2500 m a.s.l. and has been highly monitored since 2004, focusing on the microscale effects of snow ablation in Mediterranean mountains. The experimental site is equipped with a complete weather station (Table 1);
* Catchment scale--The Poqueira Alto catchment (Figure 1c). This catchment was selected as a study site to connect wet-snow dynamics with streamflow response. It is a small catchment (54.91 km\({}^{2}\)) corresponding to the headwaters of the Poqueira River. With a mean elevation of 2513 m a.s.l., its hydrological response is totally driven by snow dynamics (Table 1). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Variable** & **Refugio Poqueira (A1)** & **Poqueira Alto (A2)** \\ \hline Area & \(30\times 30\) (m\({}^{2}\)) & 54.9 (km\({}^{2}\)) \\ Average altitude (m a.s.l.) & 2500 & 2513 \\ T mean (\({}^{\circ}\)C) & 21.8/6.95/\(-\)9.55 & 12.89/7.018/0.91 \\ \multicolumn{1}{c}{} & \\ \multicolumn{1}{c}{} & \\ \multicolumn{1}{c}{} & \\ \multicolumn{1}{c}{} & \\ \multicolumn{1}{c}{} & \\ \multicolumn{1}{c}{} & \\ \multicolumn{1}{c}{} & \\ \multicolumn{1}{c}{} & \\ \multicolumn{1}{c}{} & \\ \multicolumn{1}{c}{} & \\ \multicolumn{1}{c}{} & \\ \end{tabular}
\end{table} 
Table 1: Summary of the selected characteristics of each region (see Figure 1) in the study area (SN), together with climate variables during the reference period 2016–2019.