Enhancing soil moisture-based drought monitoring in the Austrian Alps with satellite based snow masking

Alpine regions supply critical water resources for Austrian hydropower generation (60% of electricity), yet climate-change-driven droughts increasingly threaten energy production and downstream users. Effective drought early warning systems require reliable soil moisture monitoring; however, operational satellite-based surface soil moisture (SSM) products derived from scatterometer and Synthetic Aperture Radar (SAR) observations currently lack adequate snow cover masking in alpine terrain. While droughts do not occur during snow-covered periods, unmasked snow-covered backscatter introduces extreme values unrelated to actual soil moisture changes. These false signals distort statistical baselines used for anomaly detection, leading to misidentified drought events and compromised drought indicators. Existing operational products include HSAF ASCAT SSM (6.25 km) masks for all snow-affected locations, limiting spatial-temporal coverage for drought assessment, and HSAF DIREX SSM (500 m), which applies static masks regardless of seasonal snow dynamics. Satellite-based daily snow detection offers a solution by filtering unreliable soil moisture observations and enabling accurate identification of true soil moisture anomalies.

This study evaluates these soil moisture products across the Austrian Alps with and without daily snow products from combined Sentinel-3 SLSTR and OLCI data (~200 m). We validate accuracy through comparison with ERA5-Land reanalysis and in-situ soil moisture measurements. Results demonstrate that satellite-based daily snow masking substantially improves soil moisture accuracy. Both ASCAT and DIREX SSM show increased correlation with ERA5-Land. In-situ validation for ASCAT SSM reveals significant bias reduction from 0.1–0.25 m³/m³ to 0.05–0.20 m³/m³ when snow-contaminated observations are properly filtered. Validation against the 2018 Alpine drought (Central Europe's most severe in recent history) confirms that integrating daily snow products substantially improves drought indicator reliability, offering a transferable framework for early warning systems across snow-affected mountain regions worldwide.