# Synergistic Potential of Optical and Radar Remote Sensing for Snow Cover Monitoring
## 4 Results
### Evaluation of Snow Characteristics  
The major factors influencing the PSCPI in the main snow-dominated mountains of the Iberian Peninsula are latitude and elevation. The influence of elevation becomes noticeable when comparing ranges within the same elevation band. For instance, the Sierra Nevada and the Pyrenees (the highest mountain ranges of the Iberian Peninsula), both reaching elevations above 2500 m.a.s.l. (up to 3400 m.a.s.l. ), exhibit maximum PSCPI values close to 80% (Figure 4a,b). In contrast, the Cantabrian System, Central System, and Iberian Range show significantly lower values: 44%, 32%, and 27%, respectively. An intercomparison of mountain ranges within particular elevation ranges evidences that latitude predominantly influences the PSCPI across the Iberian mountains. Generally, higher average PSCPI values are observed in mountain systems located at higher latitudes, except for the Central System at elevations around 2500 m.a.s.l. where the average PSCPI is slightly lower than that of the Sierra Nevada (23% vs. 27%) (Figure 4a,e). Moreover, despite the higher latitude of the Iberian Range, it shows similar average PSCPI values above 2000 m.a.s.l. compared to the Central System (around 20%) (Figure 4d). The daily distribution of the PSCPI varies across different mountain ranges and within each mountain range according to elevation bands (Figure 5). A long-lasting snowpack exists in all Iberian mountains above 2000 m.a.s.l. A comparison at the common 2000-2500 m.a.s.l. elevation band underlines a longer snowpack duration in the mountain ranges located at higher latitudes (237 days in the Pyrenees and 229 days in the Cantabrian System), whereas snowpack durations are notably shorter in the other ranges (184 days in the Iberian Range, 182 days in the Central System, and 175 days in the Sierra Nevada). Nonetheless, at elevations above 2500 m.a.s.l. (only the Pyrenees and the Sierra Nevada), differences on snowpack persistence related to latitude are markedly reduced since the snow season length above this elevation is relatively similar (275 days vs. 244 days) (Figure 5). In the summer months, we observe that a continuous and confined snowpack persists above 2500 m.a.s.l. in the Pyrenees (PSCPI around 5%). In the Iberian mountains, snowmelt begins primarily in late March; however, this timing is strongly dependent on elevation. Snowmelt occurs progressively later as elevation increases within each mountain range. Consequently, at higher elevation in the Sierra Nevada and the Pyrenees (the highest mountain ranges), snowmelt not only starts later but also progresses at a faster rate compared to the other ranges (Figure 5). Figure 3: Aggregated climate variables sourced from the AEMET 5 km dataset to appraise the differences between Iberian montane regions over an average year for (**a**) mean monthly accumulated precipitation and (**b**) minimum, average, and maximum temperature. Furthermore, we analyzed the effect of latitude on snowpack assessing its correlation with snowline elevation under various average PSCPI thresholds. Our study reveals a consistent trend in lower snowline elevations as latitude increases (Figure 6). As expected, the Sierra Nevada consistently shows the highest snowline among the Iberian mountains, given its southernmost location within the Iberian Peninsula (latitude 37\({}^{\circ}\)). In contrast, the Pyrenees and the Cantabrian System exhibit the lowest snowline elevations, which is attributed to the fact that both mountainous regions are located at the highest and nearly identical latitudes (42.7\({}^{\circ}\) for the Cantabrian System and 42.6\({}^{\circ}\) for the Pyrenees). The Central System and the Iberian Range, situated at intermediate latitudes between the Sierra Nevada and the northern ranges (40.7\({}^{\circ}\) and 42\({}^{\circ}\), respectively), display intermediate snowline elevations. Linear correlation analysis confirms a robust relationship between latitude and latitude.