Multi-Sensor Snow Cover Assessment over the Mediterranean Region
Snow cover plays a crucial role in Mediterranean water resources, serving as a
natural reservoir that regulates seasonal water availability and supports hydrological
processes across mountainous catchments. However, monitoring snow across this
diverse and topographically complex region remains challenging due to the limited
availability of in-situ observations and high spatial variability. This study analyzes long-
term snow cover dynamics across the Mediterranean region and its four major river
basins (Po, Tiber, Crati, and Ebro) using three satellite datasets: the Advanced Very
High Resolution Radiometer (AVHRR), the Moderate Resolution Imaging Spectroradiometer
(MODIS), and the Sentinel-1 (S-1). Through a systematic comparison of Snow Cover
Ground Fraction (SCGF) data, we characterized spatial patterns, temporal trends, and
responses to extreme events across the Mediterranean region. Mean annual SCGF patterns
exhibit distinct spatial gradients, with mountainous regions displaying the highest
snow accumulation while coastal and lowland areas remain predominantly snow-free
throughout the year. MODIS data, benefiting from superior spatial resolution,
captures finer-scale spatial patterns compared to AVHRR observations.
Anomaly analyses during extreme climatic events, including the 2005 and 2022 droughts,
show spatially coherent patterns across both AVHRR and MODIS. The 2022 drought is
marked by widespread negative anomalies over the Mediterranean region. Cross-sensor
validation confirms a strong agreement between AVHRR and MODIS across most areas, with
S-1 snow depth data further supporting the accuracy of snow detection. Performance
consistency varies substantially by basin when AVHRR is compared with S-1:
mountainous regions, such as the Po basin, exhibit the highest inter-sensor
agreement, while smaller basins, including Crati and Tiber, show greater variability
due to their topography and geographic location.
Regional-scale trend analysis using AVHRR data reveals statistically significant
declines in snow cover over recent decades, although basin-level trends remain
obscured by pronounced interannual variability. These findings demonstrate the
value of multi-sensor satellite observations for monitoring snow cover dynamics in
this climatically sensitive Mediterranean region, highlighting both the complementary
nature of different remote sensing platforms and the spatial heterogeneity of snow
cover responses to climate variability.
