## Materials and Methods
### Meteorological Data  
The arid climatic conditions of the Salar de Aguas Calientes show an average of precipitations varying between 150 and 200 mm/year [23], with 10% to 20% occurring in the form of snow. The annual temperatures fluctuate between \(-\)30 \({}^{\circ}\)C to 10 \({}^{\circ}\)C, combined with strong winds leads to high evaporation rates with an average of 1500 mm per year [24].  
Since there is no meteorological station in the Salar de Talar and the Purisunchi Sub-basin study area, information on daily precipitation for the period 2014-2018 was compiled from one ground station inside the Salar de Atacama basin and two satellite resources. The ground station is in Socaire village, 49.8 km away to the northwest of the Salar de Aguas Calientes Sur, downloaded from the Agromet Home Page [25]. Accumulated precipitation was retrieved from Global Precipitation Measurement (GPM) satellite constellation and Integrated Multi-satellite GPM (IMERG). This product involves late accumulated precipitation in millimeters, over one day at \(10\times 10\) km of spatial resolution (Level 3, Version 05), downloaded from the NASA Earth Data Home Page [26]. Moreover, snow cover  
\begin{table}
\begin{tabular}{c c c} \hline
**Surface** & **Region of Interest (ROI)** & **Total of Pixels** \\ \hline Hard-pan crust 1 & S3; S5; S7; S10; S11; S13 & 600 \\ Hard-pan crust 2 & S4; S6; S12 & 300 \\ Soft pan crust & S1; S2; S8 & 300 \\ Pond & S9 & 100 \\ \hline \end{tabular}
\end{table}
Table 2: Regions of interest (ROIs) surface distribution and basic stats.  
information over the salar was retrieved from a visual analysis of MODIS Terra Corrected Reflectance, a true color product from NASA Worldview Home Page (2017).  
Precipitation events from Socaire ground station and IMERG data product and snow cover from MODIS are shown in Figure 5. The satellite data over the salar recorded precipitation events on the same dates that those of the ground station, despite its location. These precipitations events are indicative of the general trend of water supply to the salar area. Three seasons seem to be driven by rainfall and snowfall events: summer, autumn, and winter. Rainfall events were more often during the austral summer from December to mid-March, with heavy rains, electrical storms, and cooling originated eastward in the Amazon or La Plata basin which leads to the \"Altiplanic Winter\". The highest rainfall recorded over the salar was on 16 December 2018, with 7.28 mm documented by the IMERG data product. From autumn to winter, snowfall events supply water to the salar. In the autumn of 2015, an exceptional event happened on 24 March 2015, with heavy rains registered in Socaire (38.3 mm) and 9 mm snowfall over the salar registered by IMERG. Snowfalls were intensified throughout the Andean region during La Nina events (2017) (April 2017 to December 2018) with a 123-day (from 16 April to 7 September 2017) and a 64-day (10 June to 1 September 2018) period of snow covering the entire salar.  
Temperature data indicated average values of 12 \({}^{\circ}\)C for the winter months and 23 \({}^{\circ}\)C for summer, with the highest temperatures recorded during January. Figure 6 shows relative humidity (RH) through the study period. As for the relative humidity (RH), the Socaire station registered high values (38%) during the Altiplanic winter months (December to March), and an average 21% in southern winter (June to September). The wettest year was 2017 (25% average) coincident with the La Nina event and the driest 2016 (19% average). Finally, the wind does not have a specific temporal pattern.  
Figure 5: Meteorological data of the station Socaire, GPM (IMERG) and snow cover between January 2015 and December 2018, where 0 is no cover, and 1 indicates snow cover.  
Figure 6: Relative humidity (RH) registered by Socaire station over four years.  
The datasets were considered in the analysis of the results derived from the seasonality of Sentinel-1 and ALOS-2/PALSAR-2 backscattering power over Salar de Aguas Calientes Sur.