Recent decreases in snow water storage in western North America

Abstract Mountain snowpacks act as natural water towers, storing winter precipitation until summer months when downstream demand is greatest. We introduce a Snow Storage Index (SSI), representing the temporal phase difference between daily and surface inputs—sum of rainfall snowmelt into terrestrial systems—weighted by relative magnitudes. Different from snow equivalent or fraction, SSI represents degree to which snowpack delays timing magnitude inputs precipitation, fundamental component how storage influences hydrologic cycle. In western North America, annual has decreased ( p < 0.05) 1950–2013 in over 25% mountainous areas, result substantially earlier spring months, with additional declines precipitation. The associated trends offer new perspective on sensitivity climate change have broad implications for resources ecosystems.