A Dual‐Model Framework for Snowmelt Monitoring: From Spatial Cloud Gap‐Filling to the Temporal Spatial Snow Depletion Curve

ABSTRACT

Traditional snow depletion curves (SDC) fail to relate aggregated snow covered area (SCA) with the specific location of the snowline on a daily time step. This spatial uncertainty is compounded with temporal date uncertainty in cloud‐gap filling (CGF)—the process of infilling cloud covered pixels in daily remotely sensed snow cover—and limits their utility for long term forecasting. This study formalizes the spatial Snow Depletion Curve (sSDC): a dual‐model framework that anchors the temporal regression based depletion forecasts in the dynamic seasonally recurrent snow depletion pattern which is a stationary watershed characteristic. We present a dual stage architecture where Model 1 uses dynamic seasonally recurrent snow depletion patterns to resolve data uncertainty in CGF, which then serves as the foundation for Model 2—the sSDC—to convert SCA to τ * that creates a linear relationship between snow depletion and time. The ability of Model 2 to enable reliable forecasts results from the main finding of this work: that there is a linear relationship between day of year of melt out and the pixel relative timing variable ( τ *) of the dynamic seasonally recurrent snow depletion pattern. Validation across a 21‐year record demonstrates the framework's ability to track snow depletion ( R ²  = 0.97) and crucially predict final melt timing within ±0.6 days more than 2 months in advance. Testing over the Upper Snake River Basin—a large and critical water tower in the Western US that experienced a range of climactic variability—confirms the framework's robustness. Our dual‐model framework provides the high fidelity snowline on a daily timestep required for snowmelt runoff models, effectively translating static watershed patterns into dynamic, predictive temporal forecasts. The framework extracts inherent watershed characteristics and provides a promising method for application in mountainous, seasonal snow cover/snowmelt basins worldwide.