# Synergistic Potential of Optical and Radar Remote Sensing for Snow Cover Monitoring
## 6 Conclusions  
We evaluated the spatiotemporal distribution of SCA in relation to elevation and location over the main snow-dominated montane regions of the Iberian Peninsula. The Pyrenees and the Sierra Nevada display long-lasting snowpack behaviors (275 days and 244 days, respectively) related to the higher elevations existing in these mountains compared to the Cantabrian, Central, and Iberian Ranges. In the Iberian mountains, snow melting primarily occurs in the spring season. Elevation plays a crucial role in the onset of the snowmelt, with higher elevations undergoing later snow melting due to colder temperatures, which explains the long-lasting snowpack observed in the Pyrenees and the Sierra Nevada. Furthermore, we found that the snowline elevation, which determines the presence of a regular snowpack along the snow season, is strongly influenced by the latitudinal gradient (R\({}^{2}\geq\) 0.84). However, it is worth noting that other geographical factors such as the distance from the Atlantic Ocean and continentality also play important roles. Additionally, we assessed the recent impacts of climate change on SCA and found a general negative trend across all snow season months. The decline in SCA was particularly significant during the winter months (December and January). We also evaluated the potential use of SAR as a complement for the SCA spatial gap-filling of optical sensors (MODIS). Our analysis in the Pyrenees demonstrates the high potential of the combined use of SAR and MODIS, especially in spring, with proportions of wet snow contributing tothe total SCA ranging from 27.2% to 39.4% between March and May. Based on these results, we can conclude that in the rest of the Iberian mountains, where the Copernicus HRS&I SWS product is not currently available, wet snow can provide valuable additional SCA information when used in conjunction with optical sensors. Therefore, the development of the HRS&I SWS product for the Cantabrian System, Central System, Iberian Range, and Sierra Nevada represents a dynamic and engaging future line of research. Conceptualization, D.P.-V. and A.-J.-C.-L.; methodology, D.P.-V.; software, J.-D.H.-H. and C.H. ; validation, D.P.-V., A.-J.C.-L. and S.R.F. ; formal analysis, [PERSON]; investigation, [PERSON]; data curation, [PERSON]; writing--original draft preparation, [PERSON]; writing--review and editing, [PERSON], [PERSON], and S.R.F; visualization, [PERSON]; supervision, [PERSON] and [PERSON]; project administration, [PERSON]; funding acquisition, [PERSON] and [PERSON]. All authors have read and agreed to the published version of the manuscript. This research was funded by the following projects: STAGES-IPCC (TED2021-130744B-C21/AEI/10.13039/501100011033/Union Europea NextGenerationEU/PRTR), SIGLO-PRO (PID2021-128021 OB-I00/AEI/10.13039/501100011033/FEDER, UE), from the Spanish Ministry of Science, Innovation and Universities, SER-PM (2908/22; Organismo Autonomo Parques Nacionales) from the National Park Research Program, and SIERRA-CC (PID2022-137623 OA-I00) funded by MI-CIU/AEI/10.13039/501100011033 and by FEDER, UE. [PERSON] was a Fulbright Global Scholar at CSIC-IGME during this work. The AEMET 5 km climate dataset is available on the official AEMET website: [[https://www.aemet.es/es/serviciosclimatios/cambio_climat/datos_diarios?w=2](https://www.aemet.es/es/serviciosclimatios/cambio_climat/datos_diarios?w=2)]([https://www.aemet.es/es/serviciosclimatios/cambio_climat/datos_diarios?w=2](https://www.aemet.es/es/serviciosclimatios/cambio_climat/datos_diarios?w=2)) (accessed on 21 June 2023). The MODIS Terra Snow Cover Collection 6 product is available on the MODIS webpage: [[https://modis.gsfc.nasa.gov/data/](https://modis.gsfc.nasa.gov/data/)]([https://modis.gsfc.nasa.gov/data/](https://modis.gsfc.nasa.gov/data/)) (accessed on 15 May 2023).