Snow Water Storage Within Eight Pacific Coastal Watersheds in British Columbia (Canada) Inferred From Four Years of Airborne Lidar Data

Abstract Maritime mountain snowpacks are among the least understood and most poorly quantified components of global snow water storage, despite their vital role in sustaining water supplies and ecosystem health. Here, we present a 4‐year record of snow mass distribution across eight small‐to‐medium‐sized (5.2–63.4 km 2 ) watersheds within the coastal rainforests of southwest British Columbia. These watersheds, which span a collective area of ∼330 km 2 , were surveyed using airborne lidar 3 to 5 times per year to capture peak accumulation and the melt period of each year between 2020 and 2023. These surveys coincided with manual ground‐based measurements of snow depth ( n = 14,747) and density ( n = 1,912). For volume‐to‐mass conversion, spatiotemporally‐distributed snow densities were estimated (RMSE = 33.6–73.8 kg m − 3 ) using a random forest model incorporating lidar‐derived metrics, weather station data and field‐based snow density observations. Across the eight watersheds, 50%–86% of peak seasonal snow mass was stored between 1,000 and 1,500 m a.s.l., where mean winter air temperatures are close to 0°C and forest cover is prevalent. Average peak measured snow mass was equivalent to 35%–42% of total annual surface runoff, indicating that future reductions in snow water storage are likely to significantly impact downstream water availability. Furthermore, pronounced differences in altitudinal snow mass distribution between watersheds, driven by hypsometric variability and localized climate patterns, indicate that snowpack responses to warming will vary substantially across the region. The data set produced in this study provides a benchmark for evaluating regional‐ and global‐scale SWE products in mountainous maritime regions.