Hydrograph Spread Increases as Snow Declines Across the Western U.S.

Abstract The spread of the streamflow distribution throughout the water year has important implications for water availability, but the influence of changing snow on this hydrograph characteristic has not been studied. We use reference gage streamflow, the Western United States UCLA Daily Snow Reanalysis product (WUS‐SR), and snow pillow data to evaluate the relationship between peak snow water equivalent (SWE peak ), day of SWE peak (DOPS), and four measures of the width of the streamflow distribution. Across the western U.S., low peak SWE is associated with wider streamflow distributions at 63%–85% of gages, depending on measure used to assess the temporal distribution of streamflow ( p FDR < 0.1 at 43%–61%). Effects are consistent in sign but not magnitude using snow pillow data. Given expected declines in SWE peak , our results suggest water users may experience changes in water availability beyond those expected from streamflow quantity and timing alone, due to widening distributions.