Snowpacks decrease and streamflows shift across the eastern US as winters warm.

Climate change is increasing winter temperatures across the planet, altering snowmelt hydrology. This study addresses a gap in snow research in non-alpine areas by examining changes to snow and winter and spring streamflow across most of the eastern US using daily observations from weather stations and stream gages from water years 1960-2019. These daily data were aggregated across drainage basins and classified winters with similar temperatures; differences between winters and both seasonal and annual trends were statistically quantified. Winters were classified as "warm" or "cool" in each drainage basin relative to the 60-year mean; analysis of the data indicates that warm winters occur more frequently in recent decades from an average of 0.39 to 3.96 warm winters/decade from the 1960's to the 2010's respectively. Those classifications were then used to examine changes in snowpack over the same period, which shows that warmer winters have on average 50.1 cm less annual snowfall, a reduced maximum snowpack depth by 14.4 cm, and 34 more bare ground days. These changes correlate with shifts to higher winter streamflows as well as peak basin yields that are 0.02 cm lower and occur three days earlier in warm winters. In addition to altered soil moisture and stream ecosystem dynamics, these snow and streamflow changes may have negative infrastructure and economic implications including impacts to winter tourism and agriculture.