We present long-term average and annual Snow Storage Index values over mountainous western North America, intended to represent the snow water storage capacity (and associated change) across the region. The Snow Storage Index represents the temporal phase difference between daily precipitation and surface water inputs – the sum of rainfall and snowmelt into the terrestrial systems – weighted by relative magnitudes. Different from snow water equivalent or snow fraction, the Snow Storage Index represents the degree to which the snowpack delays the timing and magnitude of surface water inputs relative to preciptiation, a fundamental component of how snow water storage influences the hydrologic cycle.  Our analysis of a 64-year modeled dataset and 34-year observation dataset shows that the Snow Storage Index has decreased significantly across mountainous, western North America, due primarily to substantially earlier snowmelt and rainfall in spring months, with additional declines in winter precipitation. The Snow Storage Index and associated trends offer a new perspective on hydrologic sensitivity to climate change which have broad implications for water resources and ecosystems.

The mentioned modeled and observed datasets are publicly available and linked within this dataset and associated publication. Meteorological data (precipitation and temperature) and flux data (snow water equivalent) were used from both datasets to generate the Snow Storage Index. The Snow Storage Index is dependent on the phase and magnitude of precipitation and surface water inputs (sum of daily rainfall and snowmelt). Thus, these variables were mathematically compared annually and as long-term averages for the subsequent analysis.

R version 4.2.0 and Photoshop 24.1.1 were used to process the files and produce the following figures.